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EdgeHD backfocus with a Powermate

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#1 t-ara-fan

t-ara-fan

    Viking 1

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Posted 11 July 2019 - 11:18 PM

I have an EdgeHD 8 with a MoonLite focuser and (sometimes) a 0.7x reducer.

The numbers for backfocus are published and self explanatory.  (Here and page 15 here.)

 

For planetary, I don't use the 0.7x reducer, and I use a 2.5x  Televue Powermate to give a 5,080mm FL. 

 

What happens to the backfocus?  I recall adding a bunch of extension tubes once, but is there a less random way of setting the spacing? Or even better: knowing what it should be to save time in the field?

 

 



#2 zach540

zach540

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Posted 15 July 2019 - 03:17 AM

Never used the Powermate, but from what I've read and my interpretation of it, it doesn't seem to matter.  

 

Essentially Parfocal, and with nearly constant magnification regardless of image distance behind top surface (except 5x model which increases 1x for every 35mm of image distance increase).

http://www.televue.c...b=_app#MagChart


Edited by zach540, 15 July 2019 - 03:18 AM.



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