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Adding a Crayford focuser to an Edge SCT

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#1 joelin

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Posted 11 October 2019 - 05:29 PM

If you do this, especially for imaging, wouldn’t you lose the ideal back focus distance and no longer get round stars in the corners?

#2 junomike

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Posted 11 October 2019 - 06:04 PM

Technically yes but whether one sees a difference is the question.



#3 macdonjh

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Posted 12 October 2019 - 08:27 PM

Talk to MoonLite and/ or Starlight Instruments.  They may have a mounting flange specific for the EDGE scopes to minimize the back focus taken up by then focusers.  It's not like the EDGE scopes are rare...



#4 schmeah

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Posted 13 October 2019 - 12:58 PM

I assume you are referring to the distance that the focuser moves the chip in or out during focusing, not the original backfocus spacing required for the focuser. My 9.25 Edge has a temperature coefficient of about 90 microns/deg C, so even if the temp were to drop 10degC over the course of an evening, that is still less than 1 mm focuser movement. I’ve never noticed a difference, but I guess it would also depend on the size of your imaging circle.

 

Derek




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