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ZWO 7x50 Filter Wheel, Chroma and Astrodon Considerations

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#1 buckeyestargazer

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Posted 07 April 2020 - 06:06 PM

I was fortunate enough to receive a nearly new (but used!) ASI6200MM-Pro, 7x50mm filter wheel and M68 OAG.  I had read a few things on here about the fit of certain filters with ZWO filter wheels so I thought I'd comment also in case others needed info.

 

I have 50mm unmounted Chroma LRGB and 49.7mm unmounted Astrodon Ha/OIII/SII filters.  The Chroma filters fit in the slots just fine.  There's plenty of room in the slots around the edge, but the retention rings hold the filters without a problem.

 

The Astrodons are a bit different.  Basically, you need to make sure that the filters are well centered in the slot, otherwise the plastic retaining rings will slip over the edge along one side.  It's very tricky to get the filters centered and stay centered as you tighten down the plastic retaining rings. 

 

Although I think it would be fine like this, I wasn't 100% comfortable with it.  Those are expensive filters to not be worried about if they might slip out somehow (not likely).  So in order to help center the Astrodon filters and keep them in place I 3D printed some very thin rings/shims to go around the filters between the edge of the filter and the slot side.  It's not as easy as it might sound.  I printed the thinnest rings I could but I still had to sand the rings down so they were even thinner.  Now, the filters have enough play to still be able to rotate but also stay firmly centered in the slot.  

 

 

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#2 Hobby Astronomer

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Posted 07 April 2020 - 08:27 PM

Very nice



#3 Lead_Weight

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Posted 09 April 2020 - 07:00 PM

I'm wondering with the size of the masks, why wouldn't you just get mounted filters? Seems like they would certainly be better so long as the visible filter area was similar.



#4 buckeyestargazer

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Posted 09 April 2020 - 07:03 PM

I'm wondering with the size of the masks, why wouldn't you just get mounted filters? Seems like they would certainly be better so long as the visible filter area was similar.

Because the clear aperture is still larger with unmounted vs mounted filters.  Plus, I already had unmounted filters.  I didn't buy new ones for this.  



#5 Lead_Weight

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Posted 09 April 2020 - 07:17 PM

Because the clear aperture is still larger with unmounted vs mounted filters.  Plus, I already had unmounted filters.  I didn't buy new ones for this.  

I was more thinking out loud than questioning your purchase. I have unmounted Astrodon's in my smaller filter wheel but never had a light leak issue.

 

So, even with the filter mask, you have more clear aperture than a mounted filter?



#6 buckeyestargazer

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Posted 09 April 2020 - 07:22 PM

No offense taken or assumed!  :grin:‚Äč

 

 

So, even with the filter mask, you have more clear aperture than a mounted filter?

 

I think so, yes.  The mounted filter threads would narrow the filter wheel opening even more than it already is.  The filter masks, as you call them, are the same size as the filter wheel slot openings, so there is no reduction of clear aperture from the "masks" (they aren't really masks but the retention rings to keep the filters in place).  I hope that made sense....



#7 buckeyestargazer

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Posted 29 April 2020 - 04:42 PM

For anyone reading this thread if you would like a set of these thin rings let me know.  I'd be glad to hook you up.



#8 gatsbyiv

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Posted 29 April 2020 - 06:33 PM

This has been a problem going back to the SBIG filter wheels.  I've never liked having a screw holding down the edges of a glass filter.  Your solution should be the default one from the manufacturers!


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