Using ASI071MC-Pro With Celestron f/6.3 focal reducer/corrector - spacers needed?

pdarmody

I am using my ASI071MC-PRO for the first time with my Celestron 8se and the Celestron f/6.3 focal reducer/corrector.

What is the correct (optimal) distance between the focal reducer and the camera sensor?

How is that typically achieved?

Right now, I am using the following optical train (see attached photos):

Celestron 8se scope

f/6.3 focal reducer/corrector (Celestron # 94175)

T-Adapter-SC (Celestron # 93633-A)

21 mm spacer (supplied by ZWO with my camera)

Baader spacer (I think I pulled a 15 mm spacer out of my bag of spacers tonight)

ASI 071MC-PRO camera

I do still see some stretching of stars, especially at the edges.

What other spacer should I use to get the distance correct?

Thanks,

Pat

pdarmody

A thread on Cloudy Nights mentioned that the optimal distance between the FR and the camera sensor is 105 to 107 mm. I had seen the 105 mm value on other sites also.

I realized I had forgotten my LPSD-1 filter, so added that (sandwiched between the adapters ). This actually helped me get more distance. It turns out that the only other thing I needed was a 7.5 mm spacer, which I already had. Final optical train was

8se scope

F/ 6.3 reducer/ corrector

Adapters with sandwiched LPSD-1 filter

Celestron T-adapter

7.5 mm spacer (Baader)

ASI071MC-PRO camera

This gave me exactly 105 mm and the stars came out very round. The difference was easy to see, even in the individual sub-frames. See the new picture attached. You can't see the 7.5 mm spacer, but it's there.

Clear skies to all,

Pat

pdarmody

Better picture of new setup attached.

Hope this is helpful to others.

Pat

katherine.tsai

Thank you, Pat.