5x barlow

[hushed sigil]

Im looking for a 5x Barlow does anyone have any recommendations

[versed sky]

Why 5x

[half ivy]

why 5x

get 3X or 2X but not 5X

[hushed sigil]

i already have 3x

[versed sky]

What equipment do you have

[half ivy]

why dont you use it?

[hushed sigil]

im trying to capture mercury and you can barely see it

[versed sky]

5x won't help probably

What equipment do you have

[hushed sigil]

8” dob

[versed sky]

Oh ok

Well first you need eyepieces

Can't use a barlow without an eyepiece

[keen yacht]

What camera are you trying to capture mercury with? Also what 3x barlow do you have? You don't really need to buy anything as you can turn your 3x barlow into a 5x just by placing the camera farther away from the barlow, using some spacers. Mercury is pretty hard to get through, very low down on the horison and it's pretty small so you need to get lucky with seeing.

[hushed sigil]

oh i only have the asi120mc s and my phone

[keen yacht]

I use this formula to figure out the optimal barlow: 6 times pixel size in um divided by focal ratio. In your case that would be 6 times 3.75 divided by 6 so a 3.75x barlow should be ideal. Try adding a ~3-5cm spacer to your existing 3x barlow it should make it into something closer to a 3.75x.

Probably would be more aplicable to other planets when you have good seeing

As it would be pretty hard to get good enough seeing at the lower altitudes that mercury is at

[hushed sigil]

ill try it

[subtle root]

Hi, as someone looking for their first barlow ever. Could I get the formula a little clearer please for example:
Speed = Distance ÷ Time

[keen yacht]

This is for planetary astrophotography so not really applicable for visual: barlow multiplication(eg 2x or 3x) = 6 times pixel size in um(can google for it, eg uranus-c is 2.9um) divided by focal ratio(eg F6, just focal length divided by the aperture)

You can change the 6 to be a 7 or 8, but it depends on how good the seeing is for you.

afaik at maximum each pixel should see an area in arcseconds of around 1/4th the scopes dawes limit(120/ aperture in mm) across. I use roughly 1/3rd dawes limit where each pixel is around 0.18-0.21" across for my 8" dob with a dawes limit of around 0.6" arcseconds.

[keen yacht]

You don't really need to get a specific barlow as well, you could extend a 2x barlow into a 3x or a 4x just by putting some spacers in between it and the camera/eyepiece. As barlows are diverging lenses they spread the light out more at longer distances. Heres a chart of how it works for some televue barlows but it should be similar for others. https://www.televue.com/engine/TV3b_page.asp?id=52&Tab=_photo You can measure what distance in arcseconds each pixel is and therefore the barlow power used, by just dividing a planets current apprent diameter in arcseconds by how many pixels across it appears on the sensor