#What 250mm F4 Newt should I purchase

14 messages · Page 1 of 1 (latest)

minor locust
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Hi.

I have been doing Astrophotography for a few years. I have used a William Optics Zenisthar 73 mm refractor and a 8" celestron SCT (with 0.63 reducer). I live under bortle 5 skies with not too many clear nights per year so I have come to the conclusion that I want something faster. I was thinking a 250mm F4 Newtonina with a 1x coma corrector to start with, and once I have become comfortable with that system perhaps go F3 with Starizona Nexus 0.75 coma corrector/reducer ( which would bring me to 1 arc second per pixel roughly with my ZWO 1600 mm pro).

My image train consists of ZWO OAG, 120 mm mini guide camera, ZWO 8x1.25 Filter wheel and ZWO 1600mm pro camera, as well as a ZWO electric focuser. This sums up to around 1.2-1.3 kg.

My mount is a Ioptron CEM70 capable of 30 kg ( so I am hoping that around 20kg should be fine for imaging).

I have a permanent setup with a roll-off-roof and was hoping that collimation would be stable over a few nights in a row. Focus shift due to temperature should be of little issue with an electric focuser and a tempereature-focuse offset table I assume?

My total budget is 2000 Euro, including any upgrades needed, coma corrector, spacers, adapters, dew prevention etc.

I have been looking at the TS Photon: https://www.teleskop-express.de/en/ts-teleskope-143/photon-newtonians-from-gso-up-to-12-aperture-311/ts-optics-gso-photon-254-mm-f4-newtonian-telescope-with-steel-tube-12306 as well as the Skywatcher quattro https://www.teleskop-express.de/en/telescopes-4/newtonian-telescopes-315/newtonians-other-313/skywatcher-quattro-10-s-250-mm-f-4-imaging-newton-steel-tube-4771

I found that it was really hard to find information regarding their quality online since they constantly come with new updates regarding focusers and mechanics and that most reviews are older. In addition, many reviews are for the 150 mm versions which does seem to have a different focuser (one of the main complaints) Does anyone have experience?

slender nest
# minor locust Hi. I have been doing Astrophotography for a few years. I have used a William O...

So most F/4 Newtonians come with its issues, especially the one from skywatcher and GSO (TS). (their whole design is very cheaply made and they are money suckers because of that)

Given your goal, id recommend you put a CNC spider, mirror mask and rack & pinion focuser upgrade on your list. Furthermore, id personally replace the collimation screws with something more stable like bobs knobs, eliminating the promiennt issues they have.

Finally, you can find basically any space and adapter on aliexpress for little money, youll just have to play around to get the backfocus of the coma corrector youre aiming to get.

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A dew shield, a cover for the back of the mirror cell and a dew heater for the secondary should do a lot already to prevent dew

nocturne crystal
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Adding to that, replacing the 120mm mini with something a little more recent will be a good move

slender nest
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a 462 should be enough

minor locust
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OK Thank you both @slender nest and @nocturne crystal for your input. Do you think that it is worth going with the cheaper scopes and upgrading or should i purchase a more midrange scope such as https://www.teleskop-express.de/en/telescopes-4/newtonian-telescopes-315/newtonians-ts-photon-311/ts-photon-10-f4-advanced-newtonian-telescope-with-carbon-tube-10258 (or if you have any other suggestions).

Which one of the TS or Skywatcher is easier to upgrade in your experience (finding suitable parts etc)?

What would be the main benefit of upgrading the guide camera (bigger sensor, smaller pixels?)? Currently I dont have too many issues finding guide stars at f6.3 at 1200 mm focal length. I assumed that lower focal length and f ration would make it better.

slender nest
minor locust
slender nest
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but yes the focuser and spider are far superior to the normal photon

minor locust
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Thank you!

tropic cedar
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ide recommended stellalyra (or eqiv) 10" f4 newt and then get the replacement 3" R&P focuser. compared to a quattro the focuser is much better and the secondary spider is much stronger aswell as a large secondary. its the scope i use and it works fine tho the mirror cell isnt the best. however it only works with reducer coma correctors like a nexus or sharpstar 0.95x

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youd also want to get a replacement 300mm losmandy d plate

minor locust