Ritchey–Chrétien enjoyers thread

[crisp flower]

M82 was a big concern because it went from the First to the second in one night i think

[harsh matrix]

HUH

I think i had that happen too ngl

[slate falcon]

you should have the upper hand on light collection as you have an 8"

[harsh matrix]

when i was using the compression ring with my RC6

[crisp flower]

Ooof

[slate falcon]

we should have much more comparable results when i get the rct or class cass though

[harsh matrix]

yeah but my transparency was butt cheeks last night lol

[crisp flower]

Only time it Had Changed in that one as Well so it was pretty confusing

[harsh matrix]

it will probably remain this way until summer

next clear night on the forecast is supposed to be worse than last night

im not even thinking about setting up ngl

[slate falcon]

i had high clouds, im glad infrared exists (theres also that, i get an snr boost from ir)

monochrome cooled infrared will be so fun

[harsh matrix]

ah true

[slate falcon]

cant wait for a mono cooled cam

[harsh matrix]

if I binned x2 this is how it would have looked

the signal is much better

but so is the noise

[slate falcon]

thats a little closer!

[harsh matrix]

yeah

this is why i thought about screwing the reducer and just resampling if my SNR sucks too much

also

i love how there's no evidence of vignetting

[slate falcon]

reducers arent cool anyways

[harsh matrix]

this is peak

[slate falcon]

pure rct

[harsh matrix]

true

and by resampling down 50%, i still maintain an image size roughly of that of a 533

this might be a much more powerful strategy than that reducing bs lmao

[slate falcon]

oh yea, u no longer have a compressed light cone

[harsh matrix]

yuuuuup

[slate falcon]

honestly not bad

bigger fov than a 533 too

[crisp flower]

Not me sleeping all day because of a Migrane, Just to wake Up, See that its clear and Set Up the scope-priorities lol

[harsh matrix]

YUP

[harsh matrix]

lmao

[slate falcon]

you have your priorities right

[crisp flower]

Im in pain But its worth

[slate falcon]

im scoobert diving tomorrow so no setting up the rig :(

but i finally get to go scoobert diving after months of not going!!

basically a free morale boost still

[crisp flower]

Fair

[slate falcon]

[crisp flower]

Scope still needs to adjust to the temperature

When thats done i'll Go to sleep again lol

[slate falcon]

[harsh matrix]

After adjusting the tilt adjuster, the bright spot has navigated back towards rough center.

I think most of my misalignments may actually be present in the tilt adjuster. 🤔

[slate falcon]

[harsh matrix]

After

https://cdn.discordapp.com/attachments/1326833769495269376/1494763243296653392/image.png?ex=69e3ca40&is=69e278c0&hm=e46af73539e02bae1a7846d4a7608f4612ae4ee4bfc28d294fd4e452fed6bbc1&

Before

My sharpest images came from when this was centered.

I dunno if I should try to center it or not.

Or just leave it for the stars.

[harsh matrix]

For whoever asked, this is hall of mirrors.

It's like this all the way around the secondary.

Near perfection.

[slate falcon]

woaaaaa so cool

[harsh matrix]

Not sure i reset collimation though considering this is relative to where the primary sits.

[slate falcon]

i once got a hall of mirrors effect by threading loads of narrowband filters together

[harsh matrix]

Not relative to the current position of the camera.

💀

[slate falcon]

you need one of those lil collimation lenses to thread on the cam

[harsh matrix]

Heh

I found out a way to reset it without taking everything apart.

[slate falcon]

yooray!

[harsh matrix]

I just found out how I can adjust my mirror spacing as well.

If i want to adjust the spacing I have to loosen all of the collimation screws on the secondary.

Or else I cant turn the center screw or rotate the mirror.

[harsh matrix]

The RC is now fully zeroed out.

So next time I go out, I will have to start from scratch.

The primary is zeroed and I zeroed the secondary relative to it by using hall of mirrors again.

The tilt adjuster is fully zeroed out as well.

[crisp flower]

Unfortunately füll of Walking noise but i think the 3.8 FWHM is one the lowest ive gotten so far

[waxen mountain]

Niice

You just reminded me that this object exists

Thx

[crisp flower]

Haha youre very Welcome
I did it as a quick Test this morning, i'll think i'll give that a proper Go once i have the new focusser installed

[waxen mountain]

Here's my try

[crisp flower]

I really Love the blues

[waxen mountain]

Yee

The setup was crazy

no guiding

GTI With Oversampled Planetery CCT Setup

I don't know how the GTI managed to do that

[crisp flower]

Doesnt Matter it Looks really good

[waxen mountain]

But the colomation was giga bad

[waxen mountain]

Thanks

[waxen mountain]

This is what my setup looked like

cursed

[sinful sapphire]

4.5" CC?

[waxen mountain]

Yee

[crisp flower]

Idk it has something

[slate falcon]

YOOO

how well does it work?

[waxen mountain]

Badly

for dso

[slate falcon]

whys that?

[waxen mountain]

It's good for Planetery and Moon

[waxen mountain]

Colomation and f Ratio

[slate falcon]

were u bad at collimation?

[waxen mountain]

nope, the secondary colomation is simple but I can't colomate the primary mirror

[slate falcon]

tbf it is a visual scope

[waxen mountain]

Yea

[slate falcon]

waiit no collimatoon screws or you couldnt move it?

[waxen mountain]

No Colomation Screws

[slate falcon]

did you use it for visual?

[slate falcon]

whaaaat

i think you have to take the back off for collimation

[waxen mountain]

I haven't done visual since I was a little kid

[slate falcon]

awh :(

if i want to use my scope for visual i have to completely reconfigure it

[waxen mountain]

I recently dealt with the primary one for the first time

[slate falcon]

did it go well?

[slate falcon]

ok wtf

wtffff

no collimation screws is abysmal

[waxen mountain]

Yee

[slate falcon]

do they think they are celestron??

[waxen mountain]

The mirror is very sharp, I immediately cut my self

[slate falcon]

(celestron releases secondary only collimatable scopes)

[slate falcon]

r u ok now

[waxen mountain]

The whole quality of the Telescopes is bad

[waxen mountain]

Of course

[slate falcon]

oh

@frosty shard i think if you want a cc you will have to get a 6" after this news

or just get a long refractor

[waxen mountain]

The main screw of the secondary is broken

[slate falcon]

[waxen mountain]

Found another screw

luckily

[slate falcon]

gso does not cook with these 4.5" do they

[waxen mountain]

It's from omegon

[slate falcon]

yup, its a gso scope

[waxen mountain]

Yee

[slate falcon]

omegon is a gso reseller

[crisp flower]

Omegon is gso rebrand

Or touptec

[waxen mountain]

Ahh ok

[crisp flower]

Scopes are gso, except the baffle on the RCs, cameras are touptec

[slate falcon]

oem products 🔥🔥🔥

[waxen mountain]

My next CCT will definitely have at least Colomation screws for the primary

My Dream CCT is one from CFF Telescopes

[slate falcon]

https://www.cfftelescopes.com/product/classic-cassegrain-300-mm

[slate falcon]

YESS

same

[crisp flower]

I have Seen big RCS with gold mirrors once
Those were a dream for nir Sometime i think

[waxen mountain]

Perfection

[slate falcon]

🤤

tbh they would be so good for visual

that tiny secondary

[waxen mountain]

Do you like visual ?

[slate falcon]

i will say i dabble from time to time

im more of an imager

but when i do visual i am very happy with the results

[waxen mountain]

Results ?

in your head

[slate falcon]

yup

i do like to sketch every so often too

[waxen mountain]

Niice

[slate falcon]

i see why messier thought they were not comets while looking comet like

[waxen mountain]

Really cool

[slate falcon]

i also think those massive cct's would be insane for lucky imaging and galaxies

[waxen mountain]

Yeeeee

CCT could also be used well for DSO imo

@slate falcon

[slate falcon]

thats what im thinkin

[slate falcon]

crispy

[waxen mountain]

Good sky is one important thing for Dso Lucky Imaging

You're not aiming for the same resolution as Planetery, but you'll probably still have to be lucky with Seeing

[slate falcon]

you have to be quite lucky yea

[waxen mountain]

Yee

https://www.astrobin.com/groups/92/short-exposures-dso/

[slate falcon]

im minmaxing weight right here

a whole .1 kg

[slate falcon]

doing visual for the second time

eav

[harsh matrix]

Oh wow

[slate falcon]

@sinful sapphire

LIES

[sinful sapphire]

wqhat

i deleted this cuz i wanted to send it in general not here

[slate falcon]

ur lying tho :(

[sinful sapphire]

i am not the price is fair

[sinful sapphire]

a 20" F/4 sandwich mirror for 3250 USD is fair

considering the mirror quality

[slate falcon]

im shooting with my gs

(waiting for m27 to rise so im shooting c27 while i wait, im using my gs to ps)

@sinful sapphire cff telescopes are hand figured

[slate falcon]

AMAZING

well tbf my gs does work as a placeholder while i wait for a target change

when doing visual

[sinful sapphire]

you mean CFF Telescopes

[harsh matrix]

im going with offsets tonight

i think i have some top down tilt

not a whole lot but definitely can see it

idrc atm

the mechanical hardware tried to rip itself apart all night and im just pissed off

even the BDS is acting a little weird

i cant tell if i need to tension it up a little more or what

[waxen mountain]

Sharp

[quartz meadow]

I see some very legal discord modification right there

[slate falcon]

my brain is so firiede you sont even know

[harsh matrix]

stack

10 5 minute subs so 50 minutes of lum

no DBE

just raw af

i want to know why my stars look like diamonds

on axis

WOW

very nice color stack

same amount of data as lum for every channel

after DBE

this scope used to be like at this much data you would see fully developed problems by 15 minutes without DBE and without noise reduction

here you cant see any issues before either or after either

this is finally what I was hunting for

interesting...

the ring is faded

almost gone

dafuq

huhhhhhh

[slate falcon]

very glorious rct

[frosty shard]

Unfortunately I lost 2 hours of timelapse because of focus by wire

[slate falcon]

[harsh matrix]

ah i found it, maybe

this is almost exactly how my field looks

when just outside of focus

it's almost the same image

of course the extreme edges being worse corrected than this square CCD on a larger RC makes it harder for me to accurately asses the astigmatism

yeah

bad

i found the closer to perfectly collimated the thing gets, the sharper the corners get

DSI recommends putting the sensor back beyond focus/away from the scope, aka on the outside/rear end of the light cone/focus

like this, but I was doing the above example

I am not aware of how much of a role that plays but it will be important for this guide since the astigmatism reverses depending on what side of focus you are on

Ritchey Chretien master race

[sinful sapphire]

Harmer-Wynne mogs 🗿

[slate falcon]

i think last nights hour of data went well

-# other than having to cull 50% of the subs after the start of the meridian flip

soo i got 2 hours

but only 1 usable hour

[slate falcon]

flaths didnt fully correct

bleh

1 hour of data

[slate falcon]

so difficult to work with

gahh

[plush raptor]

where is cdk and corrected newt

[tall summit]

Look like that little Sharpstar can do some galaxy work, first galaxy test last night

[slate falcon]

uncorrected noot is the worst

[harsh matrix]

A newt isnt a cassegrain and that guide is only relevant to RC telescope designs.

[plush raptor]

ohh

[harsh matrix]

That particular part of the guide was comparing the uncorrected off axis performance of similar uncorrected cassegrains.

So they didnt include things like an SCT or a CDK

[frosty shard]

That is a lot of H-alpha on that one satellite galaxy it seems

[tall summit]

Indeed. I should have about 3-4h of clear sky tonight , will try to get a total of 7h (its 3.5h right now)

[harsh matrix]

alright I took the native image, resampled it to 65% of native, and then reduced the noise a little

easily one of the cleanest photos ive gotten from my RC's

the fact that you can already see the lower tidal tails and the upper right tidal structure in the tail streaming from the dwarf companion is crazy

this is 50 minutes of data from B8

and it already has more structure than i could get in 2 hours with my RC6, and 15 hours from my 4" frac back in the day

higher SNR from stray light mitigation + higher focal length = less light pollution per pixel, and more signal from space per pixel, resample to pack that boost into few pixels to reduce the necessary noise reduction, and it looks nice

looks sharp and very detailed too

sharp relative to the rest of the data ive seen all season

[slate falcon]

verry snazzy

[frosty shard]

A quick snapshot I took of M5

Only 21 minutes of data (6x60s per channel)

I think I need to update my hot pixel maps

unfortunately because this was a quick snapshot I didn't dither

[slate falcon]

D:

[frosty shard]

still looks good though tbh

[slate falcon]

it does yea

lack of dithering is unnoticable

[frosty shard]

The issue is all the hot pixels

[slate falcon]

ah

no darks?!

[frosty shard]

I have been calibrating with biases only + a hot pixel map

but I probably should take darks at least to get new hot pixel data

[frosty shard]

And there's 2 hours on M27

I think I need to make a collimation tweak

[slate falcon]

i wonder how much easier a cc is to collimate

[frosty shard]

A bit easier I think

Especially over a wide field

Being able to see a non-uniform comatic field helps

[slate falcon]

also, just found out systemd is implementing a base for age varification for the future

[slate falcon]

yea

[slate falcon]

next weekend ig im installing gentoo linux without systemd

[frosty shard]

Okay now you can't give me a hard time for using Arch btw

[slate falcon]

u still got systemd on it

[frosty shard]

systemdeez nuts

[slate falcon]

[harsh matrix]

https://cdn.discordapp.com/attachments/975845011260309587/1496071358176563240/M51_RC_win.png?ex=69e88c87&is=69e73b07&hm=4becb9484560ab00b29820791c9dd35da2b38db7923fac4c0b9b3eb37dd54bfb&

[slate falcon]

mmm tasty

[waxen mountain]

Nice how much Int ?

[crisp flower]

What Palette is this btw?

[waxen mountain]

@slate falcon Are the screws in the center Colomation screws?

[slate falcon]

yee

[waxen mountain]

Thank you

I wasn't very sure

[stiff mason]

And thats why I hate osc

Altho usually there is more green

[quartz meadow]

2 greens, one red and one blue

[harsh matrix]

50 minutes per channel

[slate falcon]

@frosty shard cursed IHO moment (i used just HOO for stars, left them mostly green tho bc green is fun)

[frosty shard]

SHO

[frosty shard]

What's the object? I'm guessing a galaxy and not a PNe

[slate falcon]

its a galaxy

its m94

[slate falcon]

what i did was subtract ir from oiii and ha

then subtracted oiii from ir

[frosty shard]

Not gonna lie that's kind of an insane process

[slate falcon]

so i had just star glow in ir

[slate falcon]

just continuum + oiii

and just ha

[frosty shard]

I have been wanting to do evil red galaxies for a while

[slate falcon]

they are very evil and very red

look how ourple and blue the blue looks

it contrasts and seperates so well

its kinda crazy

[frosty shard]

Here's an example of what it looks like when you have mild coma in an RC. Uniform triangular stars all pointing in a single direction, with little variation across the field.
-# @hallow berry (or someone with perms) do you mind pinning this post for future RC enjoyers to reference?

I'm pulling my scope out rn, hopefully I can quickly fix that before it gets too late

[frosty shard]

Update: my little collimation problem has been carpet bombed into submission

Turns out I had a loose primary mirror

But everything is working much better now

I also discovered that one of my mount's USB cables was starting to fail, but that problem has also been remediated

[crisp flower]

And u did Not experience crater of death with it?

[frosty shard]

Weirdly, no. And that's starting to baffle me.

[crisp flower]

Interesting.
Weird but interesting

[frosty shard]

Vel made a good point though, I'm not really able to get integrations as long as the two of you do, so if it was there I haven't been able to see it

That, and I also haven't taken very much data on both sides of a meridian flip recently.

And on top of that, I think I have a later build GSO RC than the two of you do, so perhaps something mechanical prevents that, but I'm not sure

[crisp flower]

Fair point
I dont think u are denoising your Data too much as Well which also would exaggerate the issue

[frosty shard]

Yeah my minimalistic processing doesn't pull that detail out

@crisp flower did you get rid of the crater or is it still there for you?

*Oh, and I also have the rack & pinion focuser and a lighter imaging train than Vel presumably

[crisp flower]

I did get rid of it for now, though i will Switch the focusser either way

Just in case

At least i have Not noticed it in my NGC 6951

[frosty shard]

You have the older GSO Crayford right?

[crisp flower]

Im Not Sure but i think so

[crisp flower]

Just checked, i do

After tonight, it will probably go

[harsh matrix]

what the hell

how

[sterile pendant]

For those interested by optic :

https://figshare.utas.edu.au/articles/thesis/The_optical_problems_of_the_Ritchey-Chretien_astronomical_telescope/23240819?file=40957817

[frosty shard]

Here is a crumb of data

NGC 5434

Just IR

[tight lodge]

Soooo, newtonians are superior. Got it

[frosty shard]

There seems to be a remaining gradient. Not the ring of death, but now that I think about it it might be due to some frames that were taken closer to dawn

On the other hand, I nailed the collimation

[sterile pendant]

[tight lodge]

Simpler optics, shorter focal length... AFAIK they are the best when you have about 100km of turbulent air above oversampling your data as soon as you even think of going over 1000mm of focal length 😅

Oh, and faster

[sterile pendant]

You haven't read it, have you ?

And also, do you know why RC exist ?

[tight lodge]

I'm at work... I don't particularly have the time to read it rn😂

[tight lodge]

Because Willis Ritchey had a beer with his homie Henri Chretien and said, Broooooo... what if we make a telescope that eliminates most aberrations but astigmatism?

[frosty shard]

They came up with the design independently

[tight lodge]

But my story is better

[sinful sapphire]

harmer wynne on top

[slate falcon]

false

[sterile pendant]

They created a telescope not too complicated to build, capable to offer a wide focal plane for photography plate, compact enough, mechanically stable and easy to use at large size.
The Cassegrain formula check everything except the wide focal plane and the size.
Because of the mirror arrangement, you can create a lot of different combinations. For example, DK telescope are pretty good at keeping a good image while decollimated. But the price is an awful focal plane. It is necessary to use a corrector for photography (CDK). You can't reach result as good as RC with CDK, but if we consider that the telescope is in remote and can't be collimated often, that is the right choice.
The RC are made for observatories, with high consideration to image quality.
So, in response of what you affirm @tight lodge , no, Newtons aren't better, not optically and even less mechanically. They are just more accessible (very cheaper) and easier to use in general because of the documentation on the subject

[slate falcon]

[candid flame]

you didn't really address his reasons for why newts are better tho?

[frosty shard]

Literal lies and slander, get outta here

[candid flame]

waht

i didn't say newts are better

[frosty shard]

REEEEEEE YOU LITERALLY JUST SAID NEWTS ARE BETTER

Sorry gotta gaskeep girllight gateboss

[candid flame]

fair enough

tho i guess it's fair to conclude that i would think such a thing

but i dare not say it out loud in this thread

[slate falcon]

horay :3

[slate falcon]

https://cdn.discordapp.com/attachments/1343712437828059280/1407887327082057858/togif.gif

[frosty shard]

The #1 advantage that the RC design had in a professional astronomical setting is that it has negligible distortion, which makes it ideal for astrometric measurements and mosaic building. It's not even the lack of coma (alone) that matters, but coma does introduce distortion/displaces star centroids

[harsh matrix]

i might see a little something here

[slate falcon]

jpeg compress :(

[harsh matrix]

yeah

and the variation I see is extremely low contrast

almost invisible

The design of an RC is easier to scale up in a professional setting and the field grows larger and better corrected with scale which is why they are so good

the seeing concern and being oversampled because we live at sea level isn't necessarily true either

[slate falcon]

they pretty yummy tbh

[harsh matrix]

most people don't live at sea level and geography can play a major role in seeing

like here the atmosphere is almost always calm at ground level up through the cloud layers during the summer and the fall

rarely much turbulence or energy in general

[slate falcon]

how close to the seaside do you have to be to get the positive effects btw

[harsh matrix]

which lends itself to better use with a larger, higher focal legnth telescope

[slate falcon]

ik theres some sorta laminar flow effect

[harsh matrix]

Whooptie lives near the coast of North Carolina(?) and he's about 11 miles out iirc

[slate falcon]

huh

does he get the effects of it?

[harsh matrix]

he gets sub 2" seeing on a regular basis

[harsh matrix]

i'd say so

[slate falcon]

i see

[harsh matrix]

his images are almost always very sharp and low FWHM

that's not even considering the inherent spherical aberration from him using a frac

[slate falcon]

all i know is that the wind is blowing from the closer seaside

right now

ah im 26 miles away

so theres like no way its gunna effect me tbh

[sterile pendant]

Yes absolutly. And I find this unfortunate, as it makes the practice of astronomy unequal.
At the observatory, when you have 500x on Saturn and you can’t found something to zoom even more because of the stability of the seeing, you realize there are place better than others

[tight lodge]

I'm at 15m above seal level. 😭

And about 50 miles from the north sea. So I can get very good seeing buuuuut, also a lot of bad weather because I'm that close to the sea

[hallow berry]

“RC enjoyers” thread and it’s just people having issues.

[crisp flower]

as soon as things work out, RCs are very enjoyable

[frosty shard]

People actually enjoying a glorious Ritchey–Chrétien

[frosty flicker]

what ar eyou seeing in the day

[frosty shard]

The moon was at conjunction with Jupiter and it was easy to find in the daytime

[harsh matrix]

HAHAHA

[harsh matrix]

wild

[slate falcon]

whats life without problems to fix

[hallow berry]

Enjoyable

[tight lodge]

How can you enjoy if you don't know what it takes?

[digital nexus]

Yea I still haven’t enjoyed it after 8 months

[sterile pendant]

🤩

[crisp flower]

Here i am, trying to Install the new focusser only to realized i did Not get an Adapter to be able to tread it into the scope

[tight lodge]

@slate falcon you asked to see it without BXT

[harsh matrix]

i was going to ask

💀

[crisp flower]

Needs an m90 to m68 right?

[harsh matrix]

no

there's an M90 adapter made specifically for the BDS

[crisp flower]

Okay ty

[slate falcon]

oh thats hawt 🤤

[tight lodge]

2.15"

[sinful sapphire]

Soooo…
You got a Telesco pe

[crisp flower]

lol

Guess i'll Stick with the crappy focusser for a few more weeks then

[harsh matrix]

6" SCT with a similar ring of illumination

Clearly blud didnt use flats.

[slate falcon]

EHAT THE HELL IS THAT

that is actually diabolical

[harsh matrix]

Yes

[slate falcon]

was that with an eyepeice?

or a dslr

[harsh matrix]

DSLR probably but the post does not say

[slate falcon]

its so bad

[harsh matrix]

@slate falcon or @frosty shard can I get one of you to get me an example of an RC with spherical aberration?

Id look myself but im at work

Its supposed to be clear tonight and that makes tonight collimation polishing night.

[frosty shard]

Like an image of SA?

That's going to be relatively hard to discern

If you need to set the mirror spacing, I think it's better to do it visually, though admittedly I've also been wondering about whether a short FL eyepiece will skew the perceived results

[harsh matrix]

Ye

I dont think it has any but I want to make sure tonight.

[frosty shard]

I would think that spherical aberration shows up better in the shape of the autofocus curve rather than the image

[harsh matrix]

When I reset the primary collimation screws, im certain I changed the spacing even by a fraction of a mm.

[harsh matrix]

Ah it was having issues last night out.

Sometimes it would be a perfect V and some times the right side would follow the shape of a V and then the left side would almost flatten out until the stars got too big to register.

[frosty shard]

You know how spherical aberration manifests?

[harsh matrix]

It was repeatable.

[harsh matrix]

Nope

[frosty shard]

That actually seems like SA to me

[harsh matrix]

Dunno how it looks in a curve tbh

[frosty shard]

Spherical aberration is basically the inability of an optical element to being the inner and outer rays of light to focus simultaneously

So if SA is present, it will probably skew your autofocus curve

[harsh matrix]

Hmmmmm

What's strange is i dont know why it sometimes would be a perfect V and sometimes not.

It's possible that it was happening just because it was windy that night.

I have no idea.

[frosty shard]

That should show up in the error bars of the autofocus graph, though sometimes it doesn't

I think NINA's default autofocus routine should do checks for eccentricity changes

I don't think it does at the moment

[harsh matrix]

Definitely doesnt

[frosty shard]

Maybe Hocus Focus can do it

[harsh matrix]

I doubt it because that's what im using.

Hocus focus likes to count 6 to 8 HFR stars as being 0 HFR.

[frosty shard]

Ohh I thought you were using the default NINA autofocus (which I am doing)

[harsh matrix]

Nope

I am cropping in the frame by about 20% to cut out the extreme corners because they were throwing erroneous numbers into the curve.

[frosty shard]

https://telescope-optics.net/spherical1.htm#to_the

I'd need some wave optics tooling to rigorously meausre this, but I think the shape of the autofocus curve would be flattened in front of the focal plane if the spherical aberration is negative (undercorrected) and vice versa for positive spherical aberration

The issue is that this is just ray optics, which won't tell me what the HFR curves will look like

and the effects might be partially masked by atmospheric seeing

[frosty shard]

@harsh matrix https://www.cloudynights.com/forums/topic/993316-adjusting-rc-mirror-spacing-using-an-artificial-star-field-and-hfr/#findComment-14560603
This guy seems to be getting HFRs of 1.2" or so with an unreduced RC in autofocus runs, and I'm not sure whether or not this is actually achievable. His scope also seemed to null at 1593 mm, which is way off what I expect

If this is correct I wonder if I may actually have much more SA than I thought.

[frosty shard]

https://lambermont.dyndns.org/astro/rc/Ronchi-testing-the-focal-length.pdf

This person got 1660 mm as their focal length

I am starting to wonder whether there may be more variation in the focal length of these things than has been previously mentioned

[sterile pendant]

A RC with spherical aberrations ??

[frosty shard]

Well, I did a visual test a year ago and didn't see any with my scope

But I want to go back and check it again

At least mirror spacing is easy to fix

[sterile pendant]

Yes, that is normal, there is any

Like coma

[frosty shard]

My secondary mirror was loose so I had to readjust it, but the primary-secondary spacing was actually not that difficult to adjust. Just tedious because you have to fix the secondary collimation every time

[sterile pendant]

There is astigmatism (that limit the field), field curvature, and effectivly, coma at the 5th order

[sterile pendant]

I have a question about that, do you think the use of glue for screw is interesting for this case ?

[frosty shard]

Glue for the screw?

Mine were not fixed in place in any way

If you're asking about whether I'd glue the screws or add anything to lock them in place, I definitely wouldn't

[sterile pendant]

Oups, that is not the name, sorry.
Thread locker

[frosty shard]

Honestly, the collimation stability of my RC has been extremely good, and I cart it around all the time

It does not get babied like some others' scopes and yet I only had to a major collimation adjustment after 10 months

[sterile pendant]

Oh ok, that is completly fine so

[slate falcon]

some mf is saying cosmic clarity is better than wavelets

despite all the defects it adds to the image

cc vs wavelets

cc just fries the structure

it clumps everything together

[frosty shard]

HHO is interesting

[slate falcon]

yea!

try OHO

try OHO then hue shift green to a teal

[frosty shard]

How about I try watermelon

This is fire

[slate falcon]

mortarwellon

[harsh matrix]

@frosty shard another factor to consider with the autofocus behavior i described is potential slippage in the focuser and flexture in the bracket holding the autofocuser on.

I dont think the BDS can slip, I havent been able to make it slip anyway, but the bracket does have more flex than a metal alternative.

[frosty shard]

This is the Gemini EAF bracket?

Or some other one

[harsh matrix]

No

One i 3D printed

Gemini wont work

[frosty shard]

Ah okay I was worried I may have a plastic bracket lol

What's the issue? In case I upgrade to a different focuser

[harsh matrix]

The BDS uses M6 threaded holes for an EAF bracket but the Gemini is made for use with M4 and I didnt want to drill it out, also the bracket was just barely not long enough.

[slate falcon]

y does the rct have such good framing

vs the noot

[candid flame]

0.36"/px

oversampling the diffraction is crazy work

[slate falcon]

if you dont ride the limit are you even real

[candid flame]

but no amount of lucky imaging will overcome diffraction

[slate falcon]

i know

[candid flame]

and that's not even accounting for CO

[slate falcon]

co doesnt change limit :(

[candid flame]

it doesn't?

[slate falcon]

why do you think we can connect 2 scopes and simulate a larger aperture by their distance apart

[slate falcon]

afaik no

[candid flame]

oh yeah that's right

[slate falcon]

you get a massive limit for the tradeoff of like f500

from all the missing mirror

[candid flame]

it requires fancy interferometry tho

[slate falcon]

yea

[harsh matrix]

feels wrong but it is correct

this is one of those cases of the cacophony of the masses drowning out the hard physics of resolution

[slate falcon]

im scared of physics

physicophobia

[harsh matrix]

most people are

why do you think flat earth communities are growing, not shrinking?

[slate falcon]

i was gunna do astrophysics but too difficult

maybe i will become a flat earther for free money

[harsh matrix]

because people will default to the easiest no thinking required explanation available and take it as gospel, even when math proves them wrong

[harsh matrix]

I wanted to do that too

but even ignoring the difficulty, good luck getting tenured

it's a dead end field

[slate falcon]

that too

marine biology hopefully isnt the same

[harsh matrix]

not to mention that just about every government on the planet prefers to fund their military over science so...

[slate falcon]

ya

[crisp flower]

Astrophysics would be a dream ngl
I tried myself at physics but i Had to Quit in the 2nd Semester xd

[harsh matrix]

it would have been fun if I was any good at it

unfortunately I took phyisics 2 twice and only passed it the second time because a 67 was a D and not an F

[crisp flower]

I feel that

[harsh matrix]

that was despite me quite literally being a god at calculating diffraction pattern fringes, focal lengths, etc.

oh and calculating resolution at different wavelengths

[crisp flower]

Doing the Tests at Home for 40+hours per week in Addition to lectures and Work broke me

[harsh matrix]

yeah that would have done me in too

and none of it is worth it considering the 5% tenure rate

[crisp flower]

True

[harsh matrix]

I applaud those who try anyway but I don't really see the benefit of subjecting one's self to such torture unless they are a masochist

[crisp flower]

Or an absolute genieous

[slate falcon]

masochist wont enjoy

[tight lodge]

Yeah, I've seen them posting that they have members all around the earth

[crisp flower]

globe*

[tight lodge]

Yeep

[sinful sapphire]

natural selection atp

those who are open minded realise that theyve been uhh

brainless

quite quickly and on their own

those that dont, wont ever.

[tight lodge]

Wise man

[crisp flower]

scary to see how we are progressing further and further in this direction tbh

or rather degressing

[tight lodge]

In IQ, yes, regression. As to being banned from talking... absolutely

[harsh matrix]

HAHA

[frosty shard]

The resolving power of a telescope technically only depends on the outer diameter, as it's what determines the maximum nonzero frequency of the MTF

[bleak solar]

Any good target ideas for my RC6 in the northern and eastern sky?

I need to test my new tilt plate

[crisp flower]

NGC 5907 with the new supernova

[bleak solar]

Oh neat

[crisp flower]

Thats the framing with the 8" and an imx 533

So U will be able to get some of the cool little galaxies around it in Ur frame @bleak solar

[harsh matrix]

ooooooo it's dominantly red/yellow

interesting

[quartz meadow]

how would it show up in IR?

[crisp flower]

I dont know tbh, i didnt Take nir

[slate falcon]

did u get that?

i would have got that if i didnt decide to not go out btw 😭

[crisp flower]

I was Just on the wrong target 🥲

[haughty steppe]

Yeah that's my data it was cloudy the day it actually appeared so I didn't get to capture it actually brightening like hunter outten did.

[bleak solar]

Does this look like a collimation issue?

All my stars look like this. Or is it tilt?

[slate falcon]

sorta

[harsh matrix]

@frosty shard I meant to ask you, do the stars looking like this in focus and on axis say anything in particular?

i think a lot of the fiddling ive done with the scope has caused some of the circular apertures in the system to not be circular anymore, causing this appearance

but i dont have great evidence to support that

there's flocking on the inside of the primary retaining ring that could be the culprit as that's the narrowest place that light traverses through, and that's about it

with the exception of the secondary mirror dew shield and inside and outside of the baffle tube being painted, albeit not totally smoothly

that's my current plate solved focal length

this was it in January

so it increased by 2 mm roughly

i could have introduced some very small amount of spherical aberration when i spun the secondary back and forth by a small amount

the stars lacked that diamond shape too

[frosty shard]

Ooooh, I'm not really sure. This kinda looks like how some off-axis stars have looked for me in the past, but not really? (And certainly not on-axis)

I was recently reading something about dew shields inducing their own diffraction spikes though, so that could actually be a significant factor

[harsh matrix]

right?

i didnt have my dew shield on that night

[frosty shard]

I assume you've ruled out tilt?

(Also, unrelated, but worth sharing: https://interferometer-tests.blogspot.com/2013/06/2542000-10-ritchey-chretien-gso.html)

There's actual interferometric data on a 10" GSO RC here

[harsh matrix]

nope

i havent ruled anything out

this is what Astap says

so make of that what you will

this could of course be tilt induced by the mirrors

so id take it with a grain of salt

it seems like this focuser actually has no tilt at all

i had to more or less undo every change i made for the original focuser because it was throwing this one off so badly

[frosty shard]

these results may be skewed by M51 regions being detected as stars, but idk how ASTAP handles that internally, it may throw out outliers

I would expect a lower HFR at the center

[harsh matrix]

astap's figures are not always that accurate

as far as star size is concerned

astap and pixinsight both tell different stories

oh and my M94 data comes out to 1626 mm of focal length

from 2 nights prior to M51

i adjusted the secondary mirror tilt but not the spacing

this is what astap says with the M94 data

top right is always really bad

always has been

[frosty shard]

Yeah there's some residual astigmatism, but you should be able to remove it even if the focuser induces some tilt

I also have a bad corner in my data

it's just harder to solve in my case since my sensor is smaller

https://www.ebay.com/itm/205881954962
@harsh matrix here's a Ronchi eyepiece if you're interested in getting one, I just bought the 150 lpi version

[harsh matrix]

hmmm

[frosty shard]

oh look, someone made The Mistake™:
https://photonphanatic.com/2026/04/21/rc-collimation-the-struggle-is-real/

[harsh matrix]

HAHA

yeah

this is precisely why we say not to bench collimate these things

[harsh matrix]

ya know

continuum H-alpha Milky Way looks interesting

this does support the idea that when a bunch of supernova all go off at the same time, the hot bubble they all produce tends to squish out of the plane of the galaxy rather than expanding within the galactic plane, since there's less resistance towards the galactic poles

this is a large H-alpha bubble that goes mostly ignored and it has some clear interesting structure

might be fun to image

[quartz meadow]

I wanted to say tadpoles but im not sure if it is actually.... Yeah a lot of niche regions that get overlooked

[tight lodge]

@harsh matrix Do you still have that image with walking noise?

[harsh matrix]

yes

[tight lodge]

Can i have it to experiment something?

[harsh matrix]

https://drive.google.com/file/d/1G_Nns5lI_Be-ryW7OsvyDTXKXAaS_eIV/view?usp=sharing

[crisp flower]

I know nebulae in HAlpha are Peak But May i present

Birb in HAlpha?

[frosty shard]

birb (how many seconds of integration)

[frosty shard]

Just build a mosaic of it with the RC

[crisp flower]

Birb 0.0001 sec

[slate falcon]

@frosty shard u gotta backdoor

juuust letting u know

[frosty shard]

Wat

[slate falcon]

you may want fix it

[frosty shard]

Is there a bad Arch package or something

You're leaving me hanging

[slate falcon]

nah, its a system process

[frosty shard]

Oh, just say it's copyfail

https://arstechnica.com/security/2026/04/as-the-most-severe-linux-threat-in-years-surfaces-the-world-scrambles/

for those not in the loop

[slate falcon]

have you disabled it

my dumass forgot the name

CVE-2026-31431

[frosty shard]

I literally just learned about it right now

[slate falcon]

https://nvd.nist.gov/vuln/detail/CVE-2026-31431

[slate falcon]

ah

[frosty shard]

I'm heading home and hitting that sudo pacman -Syu once I'm there though

[slate falcon]

[harsh matrix]

nah that's like 14 fovs of my RC at minimum

length wise and touching

wide

the smaller bubble next to it in Rho Ophiuchi is smaller than that thing is and I barely fit it into my RedCat's fov with the same camera

[harsh matrix]

actually this didnt even fit in the redcat's FoV

this is what that looks like

this is centered on the star Dschubba

oh my god wait

my redcat only covers the very center

💀

yeah no we arent mosaicing any of that

id rather shoot that with the rokinon

it would be like 30 frames wide with the RC

both bubbles next to each other

[frosty shard]

It would be really interesting to compare the quality of a single frame Rokinon or Redcat image with a big chungus RC mosaic with comparable etendue

[haughty steppe]

135mm Roki zoomed into 10" RC at 1500mm

Crushed the blackpoint just so theres no merge lines

[frosty flicker]

i still really wanna make a zoom in type video

[harsh matrix]

so who's volunteering to host my RC at their place that gets lots of clear skies with low bortle for free?

that's why I'm not going to waste my time doing that

it's unrealistic

[haughty steppe]

yeah, I would need over 150 frames just to get close. Not even match fov

[frosty shard]

You may never do that...but who said I wouldn't?

[crisp flower]

Technically, a colab could be possible

[candid flame]

It would also be interesting to compare it with the same integration time

Wait I'm misunderstanding etendue

How are you getting the same etendue on an RC???

[quartz meadow]

technically yes

*the collab

[slate falcon]

i think they meant same fov

same etendue would be hard

[harsh matrix]

@frosty shard inside and outside of focus look the exact same

I dont think theres any SA

[frosty shard]

Sorry it should be etendue * integration time, not just etendue

is there a unit for that?

[frosty shard]

Is that a stretched image?

[harsh matrix]

It could have been

Im not sure

I didnt check

Im in sharpcap

Also the astigmatism is entirely vertical or horizontal

Im not sure if im too close to focus or what but this isnt matching my expectations at all.

[frosty shard]

It's easier to make out detail if you disable any stretch preview

[frosty shard]

Is this far off-axis?

[harsh matrix]

Yes

Far off axis seems to slightly bias inward toward the center but it's incredibly subtle.

And yes that was stretched.

[frosty shard]

Disabling stretch is more important for identifying spherical aberration than astigmatism, so if that's the main issue you're trying to identify/fix then it's fine not to stretch

[frosty shard]

Also what were you expecting?

[harsh matrix]

Still looks identical on both sides of the focal plane

[harsh matrix]

Stars that appear more like what are in the DSI documentation, of course

Not even astigmatism across the entire field.

It doesnt even show up as being uneven unless youre at focus.

There being any astigmatism at all leads me to believe an asymmetry exists still but I dont know how to fix it when it looks the same.

Im lost.

Center field is annoyingly good.

Genuinely beautiful star.

Maybe im just thinking some weird asymmetry in the coma is looking like astigmatism

Idk

The weird corner I had looks like it fixed itself too.

Im so confused rn.

Thats my AF curve

First one.

Didn't succeed.

I think the step size is the problem but the seeing is too variable and Nina starts thinking the centroid is a star if it gets too out of focus.

The next wasnt any better

Jfc

Bruh

Also astigmatism can cause this ive found

Longer exposures are necessary here as the average makes everything pop out.

Left side has even vertical astigmatism all the way up the side of the frame.

Right side has round stars in the top right, and astigmatic pointing towards the center in the bottom right.

That's not confusing at all.

[frosty shard]

Have you tried making any tilt adjustments?

[harsh matrix]

Not yet

I would have preferred to do those last.

Screwing with it now and this is an utter nightmare

Now bobcat

Yay

Honestly @frosty shard the tilt isnt making much of a difference.

The entire left side is still astigmatic straight up and down all the way.

The right side corners are facing toward the center of the field.

Though maybe a small adjustment of the secondary mirror to the left may fix it?

Left or right idk

[frosty shard]

Have you adjusted the primary at all?

[frosty shard]

Also what's your usual autofocus final HFR?

I've never gotten anything below like 3.8 on my luminance filter

[harsh matrix]

Not tonight.

There wasnt on axis coma

[harsh matrix]

Been 2.1/2.2 but that was reduced

[frosty shard]

I think mine could still stand to be lower but there's probably still room for improvement

Especially since you're using the 571 right?

That'll inflate your average HFR

[frosty shard]

Well, the secondary mirror adjustments you need to make will induce coma

[harsh matrix]

Not really

All it took was some very very small adjustments to the secondary

I seem to have dialed it in.

Coma at the corners is even, astigmatism is symmetrical for the most part.

The rest would be a pain to perfect at this point

[frosty shard]

Can you take some out-of-focus frames for reference?

Really just one

[harsh matrix]

Af curve is a nightmare.

This sucks

I cant get a successful auto focus.

Wait it succeeded

But it looks like this

My HFR is 2.82

You can see it at the very left of the pic

[frosty shard]

Is that the previous run or did it succeed with that graph?

That is super weird

[harsh matrix]

It succeeded with that graph

It shouldn't have

[frosty shard]

Yeah, I'm shocked it didn't report a failure with that low of an R² value

Isn't the threshold for that 0.8 by default?

[harsh matrix]

Yes

And i set my threshold to 0.9

It should have failed the run.

2.9 HFR

Holy

Even my guide stars are pin points.

[frosty shard]

You're using PHD2 right? What's your HFD?

What's wild is that I don't see the Poisson spot in the defocused stars

[harsh matrix]

4.35" ish

[harsh matrix]

The seeing is quite mid

I guess my HFR says otherwise

[frosty flicker]

thoughts on guiding with a OSC camera?

[frosty shard]

wait is the PHD2 value given in pixels or arcseconds

oh it is arcseconds

[harsh matrix]

Both

[harsh matrix]

I wouldn't do it

Especially not in light pollution

Id sooner dig myself my own grave than go through that.

[frosty shard]

wait I might need to change a setting then

[frosty shard]

on an RC during galaxy season? yeah that's gonna be awful

[harsh matrix]

Just got a very good AF run

The AF run was good

Nina calculated the point of focus poorly

@frosty shard 5 minute lum sub at 38 degrees altitude came in with HFR of 2.77

Next one was 2.68

[frosty shard]

And just to be 100% sure. This is at native FL?

[harsh matrix]

Yes

Those HFR's are lower than the last few times I was out with the reducer too

[frosty shard]

AI's gonna change the world guys

[frosty flicker]

wow it knows about ic 10

[frosty shard]

No, it does not. It does not have an NGC designation, and it's in Cassiopeia.

And there's no published JWST image of it

[harsh matrix]

this crap says my work is this bad

meanwhile it is counting every single galaxy in the sub as a star

[frosty shard]

Well, looks like it's time to hunt down some globulars in M104 now...

[harsh matrix]

yup

btw

the adjustments on the secondary to fix the off axis astigmatism

were like

32nds of a turn

💀

no wonder i felt like i was going crazy

it's still not perfect and i think i cant get it there because of mechanical limitations

💀

[bleak solar]

should I test for collimation of the secondary mirror before each imaging session with an out of focus star?

[harsh matrix]

I wouldnt check every session

maybe once a week

I check everything every session but that's because I have a problem

[candid flame]

...photons

up to a scaling factor ofc

[bleak solar]

okay so it is stable enough. Cause I just got it re-collimated xD

[harsh matrix]

I would only say once a week if youre crazy

Realistically you probably never need to check it.

[bleak solar]

eh... if I know myself I will now check it every time because I am paranoid xD

[tight lodge]

@harsh matrix I need your aid! Did you design your roki adapter to have an m48 or m54 adapter?

[tight lodge]

Eh... whatever, i designed and ordered an adapter to use with my Mono P1 setup

[harsh matrix]

M 42

[tight lodge]

Oh... you got 1.25" EFW

[haughty steppe]

I run 10 second subs for my auto focus. Gives me a nice U curve. Now, if it's even slightly windy, like 6mph+ and it pushes the scope during an autofocus, I gotta redo the autofocus because it messes with the curve.

[sinful sapphire]

ikik im a bit late but theres a method for figuring it out

one star test of an RC10

it exerts slight spherical aberration based on the difference in size of the central obstruction and the fact that the edge is more defined in one ompared to the other

sign of undercorrection

(no expert here take it with a grain of salt, reflecting what I heard about figuring it out)

[tight lodge]

Uuuuhm... can someone explain why that cloud changes between mine and Hubble?

[slate falcon]

afaik that cloud is active

i remember hearing about that

but i may be wrong

[sinful sapphire]

its AI thats why

[slate falcon]

D;

[tight lodge]

THis is the oldest image i could find. it's from 2003 and the cloud appears in the same spot

[tight lodge]

[slate falcon]

so it does

thats so weird

[sinful sapphire]

fake nasa ai

[harsh matrix]

That loos like an artifact

[slate falcon]

maybe i will download hubble data from this location over the span of like 4 years

[slate falcon]

@tight lodge no, checked and its just the star cluster moving

(that i heard it from)

[candid flame]

Your image also has an extra star?

[tight lodge]

Blame stellarium

[slate falcon]

m16 was visited a lot

[candid flame]

Fair enough

[tight lodge]

Also, this is the Hubble survey in Stellarium🤣

Definitely something weird happening

[slate falcon]

these are like 8 years from start to finish

[tight lodge]

Blink em

[slate falcon]

ye!

[slate falcon]

it all failed

[harsh matrix]

dont download em all at the same time

[slate falcon]

ive used all energy so ksp time

[harsh matrix]

this is hot

i wish i prioritized MW star clouds earlier

this would have been quite a lot better without the moon

my goal was to shoot the Sombrero galaxy all night but it took too long for me to address the problems with the secondary mirror and tilt

wish it wasnt the full moon

[frosty shard]

This seems too far out of focus to really highlight the differences tbh

[frosty shard]

Well, etendue * integration time will give you wildly different numbers of photons if you're imaging the moon vs. a dark nebula lol

[tight lodge]

@harsh matrix I designed and ordered an M54 to M48 adapter in about 30 minutes. What could go wrong?

[harsh matrix]

a lot could go wrong, probably

[frosty shard]

I should point out - the last time I was out fixing my collimation, I had to make significantly larger adjustments than I expected to actually get the astigmatism to move

And it required me to adjust the primary mirror

[harsh matrix]

ah

well i had just reset my primary mirror's position the night before last, and adjusted out the coma that was left

it didnt require large adjustments either

my scope completely zeroed out is super close to collimated

that's why i went through that process of hall of mirrors in the first place

something about this scope is mechanically aligned very well and i planned to harness that and use it to my advantage

use known positions to start and then make small iterative adjustments to resolve the rest

seems like it worked.

[frosty shard]

Just to be clear - you know the primary and secondary mirror both produce coma when they're misaligned right

[slate falcon]

no im not

[harsh matrix]

yes

[slate falcon]

ckan crashed

after i selected pbc

aaand i cba to re select every mod

[harsh matrix]

however you can only collimate to the best the seeing will allow

and the seeing said there was not any coma, last night.

[frosty shard]

(I need to do a raytrace of an RC to simulate the apperance of different kinds of misalignment tbh)

[harsh matrix]

i think there's some tilt along the vertical axis of the camera but i can resolve that some other time

it's not as bad as ASTAP claims it is

[harsh matrix]

mine does seem to have some slight left to right mechanical offset

if you look at the uncalibrated subs above

that's the position where the left and right side match the best

[slate falcon]

do you have the 8" values

[frosty shard]

I think someone posted them on Cloudy Nights

[frosty shard]

somewhere in this thread: https://www.cloudynights.com/forums/topic/840516-gso-rc8-mirror-details/

I think the primary is f/3

[candid flame]

That's where the scaling factor comes in lmao

But for the same target it should be the same

[harsh matrix]

i think im going to print my M16 photo here in a little bit, just to see what it looks like coming out of a printer

if it looks good ill unironically order the first print of my own work from a professional company

[candid flame]

So in actuality it's probably signal per object irradiance or something like that

[harsh matrix]

I LOVE THE MOON

[slate falcon]

hoo?

hoo hoo

[harsh matrix]

now astap says this

[harsh matrix]

rgb

💀

[slate falcon]

oh

[harsh matrix]

honestly it is cleaner than i expected

especially for being near the moon

[tight lodge]

But I made a .step file and a technical drawing.

[harsh matrix]

did you factor in tolerances

[tight lodge]

Yep

[tight lodge]

ISO 2768-2, close enough is good enough

Why Fusion360 doesn't have AstroISO metric threads?

[harsh matrix]

i dont know and it makes me angry

[tight lodge]

Well, you don't need them for JLC CNC

[harsh matrix]

didnt need them for PCB Way either luckily

still makes me angry

LMAO

okay this little thing

fills the frame

that's exactly why i wanted to give this a go

considering this

didnt even hit me how well this fits until i played with the idea last night

almost did this instead of M104

[sinful sapphire]

Exactly what the guy who analysed it said too lol

[harsh matrix]

@frosty shard dont feel bad about voting for Antennae lol

everyone is voting for that

I think my incredible process of Hubble's got em all riled up