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Help with choosing 1.25" vs 2" filters

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#1 jroden144

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Posted 25 January 2021 - 11:00 AM

I plan on buying a dedicated astronomy camera within the next several months and would like to incorporate a filter system in the image train at some point.  An electronic multi-position filter wheel would be nice but if budget doesn't allow, a manual filter wheel will work just fine.  My question is, is there any advantage to using 2" filters over 1.25"?  Of course, 2" will be more expensive but if I end up going with a ZWO 1600MM-Pro or a 294MC-Pro, would 1.25" filters suffice?  I would assume 2" filters would be geared more toward visual observing for 2" eyepieces.  I see you can buy filter wheels that accept either 1.25" or 2" eyepieces.



#2 Slice1969

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Posted 25 January 2021 - 11:10 AM

I can only comment on what I have, but 1/4" filters are a good fit for a 183MM Pro.



#3 sg6

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Posted 25 January 2021 - 11:16 AM

The "problem" of a 1.25" filter is they have an aperture of (reasonable measurement) of 15/16" or 23mm.

The "hole" bit is less then 1.25".

 

They have the threaded housing to fit into a threaded 1.25" female housing but that means they are somewhat smaller and the greater the housing they are supplied in, then the smaller the aperture. One of mine is really small.

 

So the big risk is therefore vignetting just because they are too small and the distance from the sensor is relevant - the further away then the bigger they need to be.


Edited by sg6, 25 January 2021 - 11:18 AM.

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#4 Midnight Dan

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Posted 25 January 2021 - 11:24 AM

The 1600 and 294 are both micro four-thirds sized sensors, so 1.25" filters will be perfectly fine for them.  With those cameras, there won't be any advantage to using 2" filters.

 

However, if you want to future-proof your setup, 2" filters can be a good investment.  Moving to an APS-C or full frame sensor in the future will require filters larger than 1.25" to avoid serious vignetting.  Of course, 2" filters are more expensive and the filter wheel is larger and heavier, so those are the tradeoffs.

 

-Dan


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#5 happylimpet

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Posted 25 January 2021 - 12:02 PM

I use a 1600 with 1.25" filters. There is vignetting but flats deal wth it. This is at f2.9, so at more sensible f ratios it deffo wont be an issue.


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#6 jroden144

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Posted 25 January 2021 - 12:38 PM

The 1600 and 294 are both micro four-thirds sized sensors, so 1.25" filters will be perfectly fine for them.  With those cameras, there won't be any advantage to using 2" filters.

 

However, if you want to future-proof your setup, 2" filters can be a good investment.  Moving to an APS-C or full frame sensor in the future will require filters larger than 1.25" to avoid serious vignetting.  Of course, 2" filters are more expensive and the filter wheel is larger and heavier, so those are the tradeoffs.

 

-Dan

Thanks Dan this is great info.  Helps a lot.




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