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Backfocus for ES 2" - Field Flattener (for QHY168c) 45mm or 55mm?

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#1 Hare314

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Posted 11 January 2019 - 04:12 PM

I am really confused on the backfocus requirements for the Explore Scientific 2" Field Flattener.  I read on several websites that "Working distance = 1.77" / 45mm".  However, I read on forums that it is 55mm.  

 

From what I have also read the 55mm is for DSLRs and 45mm is for CCD/CMOS?  I just want to confirm this.  

 

Also, from where on the flattener is the measuring point for proper backfocus?

 

Many thanks for any helpful insights  smile.gif



#2 Gadroc

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Posted 11 January 2019 - 06:11 PM

I have mine spaced at 45mm and it works well. ES now sells special versions with low profile adapters for DSLRs, which they would not need to do so if it was 55mm.
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#3 Hare314

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Posted 11 January 2019 - 06:39 PM

Thanks Gadroc :)

 

I will measure out to 45mm.  However I do not know at which physical point of the reducer to start (or finish) the measurement.  Is the measure to start at the actual optic of the flattener?  Or the threads?  



#4 Gadroc

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Posted 11 January 2019 - 06:57 PM

I measured from the flat shoulder of the flatener where the threads start.



#5 Hare314

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Posted 11 January 2019 - 07:19 PM

Ok great thanks again!  I appreciate the quick responses 




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