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Old 11-06-2021, 12:43 PM
evltoy (Wayne)
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evltoy is offline
Join Date: Sep 2020
Location: Melbourne
Posts: 124
Back focus with my DSLR and SCT with reducer

Hello All,

I hope everyone is keeping well

As some may know, I have been battling with getting the right back focus distance with the introduction of a x.63 Celestron Corrector/reducer on my 8" SCT. Last night I was able to sneak in 2hrs of testing while the skies were somewhat clear.

Here is what I did.
1) Using my Alt/AZM mount align etc..
2) Using a Bahtinov mask, get the right focus on a bright start
3) Slew to NGC104 and took the best 30sec exposure
4) Change distance down by 5mm
5) repeat steps 2-4

The only thing I didnt do is frame up the target like for like. Should I have done this?

Anyways I have attached the single shot images for review. If you have the time please have a look and tell me which image feels right or getting close to perfect.

The setup is a Celectron 8" SCT with Celestron .63 Corrector/reducer, 2" rings to a Nikon D600 (using DX mode).

Attached Thumbnails
Click for full-size image (Single__D60_1308_back_fouse_testing_2021-06-10_30s_ISO800_50mm__NA.jpg)
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Click for full-size image (Single__D60_1314_back_fouse_testing_2021-06-10_30s_ISO800_40mm__NA.jpg)
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Click for full-size image (Single__D60_1319_back_fouse_testing_2021-06-10_30s_ISO800_35mm__NA.jpg)
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Click for full-size image (Single__D60_1324_back_fouse_testing_2021-06-10_30s_ISO800_30mm__NA.jpg)
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Click for full-size image (Single__D60_1330_back_fouse_testing_2021-06-10_30s_ISO800_25mm__NA.jpg)
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Click for full-size image (Single__D60_1335_back_fouse_testing_2021-06-10_30s_ISO800_20mm__NA.jpg)
139.2 KB32 views

Last edited by evltoy; 11-06-2021 at 12:53 PM. Reason: spelling
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Old 14-06-2021, 12:54 PM
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AdamJL is offline
Join Date: Sep 2010
Posts: 963
Hi Wayne

I would say the two sharpest are these:


hard to choose between those two.
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Old 15-06-2021, 02:41 PM
evltoy (Wayne)
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evltoy is offline
Join Date: Sep 2020
Location: Melbourne
Posts: 124
Hey Adam,

Thanks for taking out the time to look & comment. I appreciate you helping me out.

I too picked one you did

But I went the other way on my second

My main focus was trying to find the most roundest stars on the outer sections of the image.

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