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Vignetting on Celestron C6 SCT & f6.3 focal reducer field flattener

Astrophotography Catadioptric Celestron DSO Equipment Imaging SCT
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#1 nikulsuthar

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Posted 29 September 2022 - 12:59 AM

Hi All,

 

Many thanks for taking time to read my below question.

 

Has anyone tried to do DSO long exposure imaging with Celestron C6 SCT and Celestron f6.3 focal reducer field flattener along with a 4/3rd micro chip sensor (e.g. ZWO ASI 294MC/MM or ZWO ASI 1600MM)? If yes then have you experienced any vignetting in your subs? This is because the orange tube body Nexstar 6SE has only 1.25" of visual back (hole diameter at the back of the telescope body). Considering 105mm of back focus distance on Celestron f6.3 focal reducer field flattener this should most probably cause vignetting. Please let me know if you have any such vignetting experience.

 

Thanks,

Nikul

 



#2 EGregerson

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Posted 29 September 2022 - 01:44 AM

My usual answer is 

I don't know , but'.  Is the image OK without the focal reducer? 


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#3 rob1986

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Posted 29 September 2022 - 03:59 AM

Hi All,

Many thanks for taking time to read my below question.

Has anyone tried to do DSO long exposure imaging with Celestron C6 SCT and Celestron f6.3 focal reducer field flattener along with a 4/3rd micro chip sensor (e.g. ZWO ASI 294MC/MM or ZWO ASI 1600MM)? If yes then have you experienced any vignetting in your subs? This is because the orange tube body Nexstar 6SE has only 1.25" of visual back (hole diameter at the back of the telescope body). Considering 105mm of back focus distance on Celestron f6.3 focal reducer field flattener this should most probably cause vignetting. Please let me know if you have any such vignetting experience.

Thanks,
Nikul


Me no, but there are quite a few questions an this topic and some images.

What the images have shown is that in general the c6 does not cope well with focal reducers.
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#4 Tapio

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Posted 29 September 2022 - 04:15 AM

Do you already have the reducer?
You could search astrobin for such combo.

Here's one
https://www.astrobin.../6y25bq/?nc=all
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#5 daveco2

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Posted 29 September 2022 - 05:01 AM

Not surprising going from f/10 to f/6.3. The image circle gets reduced accordingly, aggravating vignetting.  See the write up on Agena Astro regarding focal reducers.


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#6 nikulsuthar

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Posted 29 September 2022 - 07:31 PM

My usual answer is 

I don't know , but'.  Is the image OK without the focal reducer? 

I've captured Moon and planets without the focal reducer where I did not see much vignetting. But doing long exposure DSO imaging is a different story altogether and flat frames are critical...



#7 nikulsuthar

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Posted 29 September 2022 - 07:35 PM

Me no, but there are quite a few questions an this topic and some images.

What the images have shown is that in general the c6 does not cope well with focal reducers.

No... On the product page of the f/6.3 focal reducer they have mentioned C6 in the comptibility list and I believe that it should work... But with the steeper light cone at f/6.3 as compared to f/10 might induce vignetting. I may try with the camera to test it out...



#8 nikulsuthar

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Posted 29 September 2022 - 07:36 PM

Do you already have the reducer?
You could search astrobin for such combo.

Here's one
https://www.astrobin.../6y25bq/?nc=all

The Astrobin link is great... I did not see vignetting there that too with an APSC DSLR sensor... I think that this answers my question of less chances of vignetting... Thank you.... waytogo.gif



#9 nikulsuthar

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Posted 29 September 2022 - 07:42 PM

Not surprising going from f/10 to f/6.3. The image circle gets reduced accordingly, aggravating vignetting.  See the write up on Agena Astro regarding focal reducers

Not till now... I read it and found very useful... Many thanks for mentioning it... waytogo.gif



#10 EGregerson

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Posted 29 September 2022 - 09:42 PM

I'm thinking 2" visual back; i note u have a 9.25; that should have a 2". any issues with the 6.3 on that ota? 


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#11 rob1986

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Posted 30 September 2022 - 08:10 AM

No... On the product page of the f/6.3 focal reducer they have mentioned C6 in the comptibility list and I believe that it should work... But with the steeper light cone at f/6.3 as compared to f/10 might induce vignetting. I may try with the camera to test it out...


On this forum is an impressive example of full frame formatting with heavy vingetting from a c6
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#12 nikulsuthar

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Posted 03 October 2022 - 12:25 AM

I'm thinking 2" visual back; i note u have a 9.25; that should have a 2". any issues with the 6.3 on that ota? 

The hole at the back of the optical tube is 1.25" in my C6 but is 2" in my C9.25. So even by using a 2" visual back adapter I cannot increase the diameter of the light cone...



#13 nikulsuthar

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Posted 03 October 2022 - 12:26 AM

On this forum is an impressive example of full frame formatting with heavy vingetting from a c6

Thanks for the pointer... I'll search it out and see whether I find any clue...



#14 rob1986

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Posted 03 October 2022 - 01:17 AM

Thanks for the pointer... I'll search it out and see whether I find any clue...

I tried to find it in my history but didn't manage due to time constraints

The image was beautifull, but you could literally see the shadow effects of every stupid piece of baffling, the mirror at the same aperture as the corrector, and the vignetting imposed by secondary size.

Honestly pictures like it ahould be pinned with milimeter scales and all info on the OTA for 1answering questions like these in great detail

Edited by rob1986, 03 October 2022 - 01:20 AM.



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