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Confirming Back focus on QHY183c

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#1 plot0015

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Posted 16 September 2020 - 01:30 PM

So i just opened up my new/used (thanks to this site) QHY183c.

 

I think I am just making sure i have my thought process down for my imaging train.  i'm gonna have a QHY183c camera, and a 2" HOTECH SCA Field Flattener,  then FF ties to the 2 inch "plug" into my ES-ED80...

 

Looks like the QHY has a backfocus/chip offset distance of 17.5 to 18mm.  (per this page  )

And Looks like the Ho Tech needs a total back focus of 55mm  (per this page   )

So I think that means i need roughly 37mm of extension tube between the QHY and the FF ?   



#2 SilverLitz

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Posted 16 September 2020 - 01:37 PM

Yes, that sounds right.  The distance from the exit of the FF to the image sensor should be ~55mm.  Make sure you are measuring the from starting point of the FF that the manufacturer defines this distance from.


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#3 plot0015

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Posted 16 September 2020 - 01:49 PM

sorry... just notice my links didn't post....   but i think i have some good visuals on the FF.



#4 calypsob

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Posted 16 September 2020 - 02:00 PM

What adapter do you have on it? The cone shaped adapter gives you 18mm backfocus.


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#5 plot0015

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Posted 16 September 2020 - 02:16 PM

right now i think the cone shaped adapter is running a M42 thread which matches the M42 thread on the hotech ff.... initially i screwed the FF right onto the camera and after staring at it....i thought... "that ain't right"  i need more space here....



#6 plot0015

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Posted 16 September 2020 - 02:16 PM

https://www.hotechus...l - sca ffl.pdf



#7 plot0015

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Posted 16 September 2020 - 02:22 PM

So QHY  (with 18mm backfocus) >>>>> ~37mm in spacers >>>>> Ho Tech SCA>>>>> Extendertubes>>>>> Plug>>>>>  ES-ED80

 

also.  i have ordered a 20,15,10, and 5 Extender....   so right now i have 35mm...  whats the best way to get to 37mm? i'm struggling to find 2mm spacers


Edited by plot0015, 16 September 2020 - 03:42 PM.


#8 1DegreeN

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Posted 16 September 2020 - 09:55 PM

Perhaps you could try a Baader varilock extension to easily nail down the correct backfocus and then you could replace it with the correct spacers and sell it on if you have no further use for it. Although the backfocus should be 55mm from FF, in practice it could be 1 or 2mm away.



#9 KTAZ

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Posted 16 September 2020 - 10:03 PM

So QHY  (with 18mm backfocus) >>>>> ~37mm in spacers >>>>> Ho Tech SCA>>>>> Extendertubes>>>>> Plug>>>>>  ES-ED80

 

also.  i have ordered a 20,15,10, and 5 Extender....   so right now i have 35mm...  whats the best way to get to 37mm? i'm struggling to find 2mm spacers

This vendor has rings in various sizes and includes 1mm. Send them a PM.

 

https://www.cloudyni...pacer-rings-12/



#10 plot0015

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Posted 17 September 2020 - 06:51 AM

Thank you!




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