50mm vs 2" filters

Equipment Filters Filter Wheel
7 replies•190 views
Dan Brown avatar
Dan Brown avatar
Howdy all. I'm new to the filter game and hopefully I didn't make a mistake purchasing 2" filters. I have on order an epsilon 160, pegasus filter wheel, and short back focus length QHY600. I also ordered astronomik max fr 6nm 2" filters. Do you think I will have vignetting issues? I could return them and get the 50mm size.
Thanks for your help.
Dan
Marc Agostini avatar
Marc Agostini avatar
Hi,

I always found this calculator helpful, because it depends on the distance between the filter and the sensor as well as the focal ratio of your scope:

https://www.starcanvas.org/calculators/filter-aperture-calculator


Clear Skies, Marc
wittinobi avatar
wittinobi avatar
hmm, 2" = 50,8mm
…am i wrong?
kuechlew avatar
kuechlew avatar
hmm, 2" = 50,8mm
...am i wrong?

2" filters are threaded and can be used without a filter wheel, 50mm filters are not. Owners of filter wheels seem to prefer the unthreaded filters.

Clear skies
Wolfgang
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Dan Brown avatar
Dan Brown avatar
Marc Agostini:
Hi,

I always found this calculator helpful, because it depends on the distance between the filter and the sensor as well as the focal ratio of your scope:

https://www.starcanvas.org/calculators/filter-aperture-calculator


Clear Skies, Marc

Dang, looks like I need the 50mm filters. I will have to return my 2" and wait. Thanks Marc.
Dan
Marc Agostini avatar
Marc Agostini avatar
hmm, 2" = 50,8mm
...am i wrong?

Almost! the thread is for the inside of a 50,8 mm barrel (outside diameter), so it is 48mm but depending on the manufacturer the free aperture is more like 46mm. But now you mention it you won't get the full 50,4 mm on such an unthreaded filter, since the lip on the filter wheel will cause some obstruction. My filter slider for 50,4mm filters comes in at 49,2mm free aperture for example. So in the end the difference is about 3mm

Clear skies, Marc
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Marc Agostini avatar
Marc Agostini avatar
Dang, looks like I need the 50mm filters. I will have to return my 2" and wait. Thanks Marc.Dan

You're welcome, glad I could help!

Marc
Andy Wray avatar
Andy Wray avatar
I learned something here about my ASI1600MM Pro. 

I had always assumed that it had a 4/3rd inch sensor as the ASI web site shows the diagonal as 4/3".  In fact the active sensor diagonal for a Four Thirds sensor is 22.2mm.  That explains why I can get away with 1.25" filters with the ASI1600MM.

Thanks for sharing the link to the calculator.
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