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Tak FSQ85 and 1.01x Flattener issues….

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#1 AstroOlly

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Posted 05 October 2022 - 03:27 AM

Hello,
I have the Tak FSQ85 and due to bad stars at the edges of the FOV due to using a new QHY268c with small pixels, I have had to buy the dedicated flattener, now `tak brought this flattener out purposely for this issue, even though these scopes have a built in flattener, it’s not good with large sensors and small pixels…
so my question is to anyone with this set up, the backspace for the flattener is 56.2mm, how critical is this ..???
I have my spacing at 57 and I have a 2mm filter in the light path so that adds 0.66mm to the 56.2 so am pretty close to the 56.8..required for this setup
so would like to hear from others about this spacing and how critical it is…
thanks all 
Olly



#2 imtl

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Posted 05 October 2022 - 03:30 AM

Forget about the required spacing. Just experiment with it until you get the field perfected as possible

#3 AstroOlly

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Posted 05 October 2022 - 03:39 AM

Forget about the required spacing. Just experiment with it until you get the field perfected as possible

Thanks, but not really what I was asking, I want to hear from people who have this set up for some guidelines on how critical, when I can I will test, but for now just wanting some advice 



#4 Mike7Mak

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Posted 05 October 2022 - 04:20 AM

I have my spacing at 57 and I have a 2mm filter in the light path so that adds 0.66mm to the 56.2 so am pretty close to the 56.8..required for this setup

I could be wrong but doesn't the filter add that .66 to your 57mm not the flattener's 56.2mm? I was under the impression that filters add to the image train length not subtract.


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#5 AstroOlly

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Posted 05 October 2022 - 05:12 AM

I could be wrong but doesn't the filter add that .66 to your 57mm not the flattener's 56.2mm? I was under the impression that filters add to the image train length not subtract.

thanks for your reply…appreciated…
Yes, I just did not explain it well above, I have my spacing at 57, but with the filter it requires 56.8 (my filter is 1.8mm thick) so I am .2mm over, and just wondered whether this would be within tolerance for the flattener…



#6 Mike7Mak

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Posted 05 October 2022 - 06:27 AM

Ok again, I'm not 100% totally certain about what I'm saying but...

 

If the spacing physically measures 57mm, with the filter in line it's actually 57.66mm of light path. The filter adds to the physical spacing not to the flatteners backfocus. I believe the flattener still requires 56.2mm which means you're a little farther from optimum than you think.

 

At any rate your main question is how critical the backspace distance is, and that I don't have a clue. Sorry for the distraction.



#7 AstroOlly

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Posted 05 October 2022 - 11:11 AM

Ok again, I'm not 100% totally certain about what I'm saying but...

 

If the spacing physically measures 57mm, with the filter in line it's actually 57.66mm of light path. The filter adds to the physical spacing not to the flatteners backfocus. I believe the flattener still requires 56.2mm which means you're a little farther from optimum than you think.

 

At any rate your main question is how critical the backspace distance is, and that I don't have a clue. Sorry for the distraction.

No, you are not correct there, the filter just adds to the backfocus of the flattener….my flattener back spacing physically measures 57mm the flattener requires 56.2, plus I have to add 0.6mm for a filter so I need a spacing of 56.8, (56.2 + 0.6 = 56.8mm)  so as I am at 57mm I am 0.2mm over what is needed….does that now make more sense to you….


Edited by AstroOlly, 05 October 2022 - 12:12 PM.



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