Setup Help

[Kenboy]

Hey all,

I've a Celestron 76eq scope (3" aperture, 700mm focal length), DSLR and star adventurer mount. Trying to do some AP with this setup (I know, not ideal :P, but want to give it a shot anyways)

I'm finding it quite difficult to get focus, I can manage a clear picture by connecting a T adaptor, 15mm eye piece and a 3x barlow 

But I think this would give me way too much magnification for DSOs, and also put a strain on my tracking.

Any suggestions on how I can modify my setup to maintain focus and get reasonable pics? 

Thanks !

[MimasDeathStar]

You may want to reconsider your setup.

You will have several challenges to overcome:

•  The 76 eq has a spherical not parabolic mirror which means that you are going to struggle with focus either way - and probably have some fuzziness at the edges even if you can get the centre in focus.
• The 76eq wont reach focus with a camera as the focusser doesnt have enough inward travel to reach focus.
• You have discovered this - and that is why you have managed to get around it with your barlow and eyepiece. However...
• The longer the focal length the more difficult it is to track. On top of this, you need much longer exposures than you would with a short focal length.
• You now have a focal length of 2.1metres - ignoring the 15mm eyepiece. This is absolutely gargantuan! 
• The star adventurer is not comfortable with focal lengths above 300mm or so. So you see your problem
• Additionally the long tube of the 76eq will make balancing your setup on a star adventurer a challenge due to the long tube length.

The only possible advice I can give you is to totally abandon the idea of using this scope for astrophotography. You will achieve exponentially better results just using your dslr on your star adventurer with lenses up to about 300mm.

edit: you would have to physically shorten your scope tube to achieve focus with a dslr

Edited July 5, 2020 by MimasDeathStar

[Kyle Allen]

I agree with the above comment. Being around F/9 you will need very long exposures to capture a significant amount of signal and this only adds to the challenge of a long focal length. 

[Kenboy]

Thanks both

Really helpful !

I think I'll just try my DSLR + 50mm F/1.8 lens and see what I can get 

[happy-kat]

Though that focal length on the Moon might be interesting and exposures there would be pretty short

[Kenboy]

On 05/07/2020 at 15:07, happy-kat said:

Though that focal length on the Moon might be interesting and exposures there would be pretty short

Turns out, even with 15mm eyepiece and 3x Barlow, I couldn't get focus on the Moon. 😛