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36mm filters in 2" filter wheel?

ZWO ASI2600MC Pro Filter Wheel Monochrome One-Shot Color
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John Walsh avatar
John Walsh avatar

Hi all,

I was set on moving from DSLR to mono this year but I think I will go with and ASP-C OSC(2600MC pro) in the end.

There hasn’t been a fully clear night since the end of September and I’m not sure if I would be able to make the best use of Mono in practical terms.

Mono is something I might upgrade to in future.

With this in mind, I am thinking of getting the OSC camera with an EFW, with a view to using the same EFW if and when I do go Mono.

The convenience of not having to redo flats, automating a broadband and dual NB session, as well as having a dark filter for doing my darks being the principal reason for the EFW in the first place.

The dual narrowband filters being mostly 2”, it will have to be a 2” filter wheel.

However I would not like to have to get 2” mono filters which are significantly more expensive than their 36mm unmounted counterparts. So I am wondering if there exists and adapter that can accommodate a 36mm filter in a 2” filter wheel? Not sure if this is even a good idea or not.
Perhaps a filter drawer is the better option..
What do people think?

Many thanks in advance

Respectful
andrea tasselli avatar
andrea tasselli avatar
A filter drawer is a way cheaper and practical option for sure. You can still get most if not all the filters you might need in the 36mm variants. As far as I know there are 36mm adapter for mounting on a 2" carousel but if you aren't planning for a FF in a future that would be essentially pointless.
John Walsh avatar
John Walsh avatar

andrea tasselli · Nov 9, 2025, 05:26 PM

A filter drawer is a way cheaper and practical option for sure. You can still get most if not all the filters you might need in the 36mm variants. As far as I know there are 36mm adapter for mounting on a 2" carousel but if you aren't planning for a FF in a future that would be essentially pointless.

Thanks Andrea. I suppose I was looking at dual NB like the L-Ultimate etc and they seem to be only either 2” or 1.25”

andrea tasselli avatar
andrea tasselli avatar
It would be probably less expensive and complicated to get another carousel when and if switching to mono down the road.
SonnyE avatar
SonnyE avatar

I just went for a 2” drawer for my use. Jumping right over the 36mm.

My reasoning is as simple as the bigger sweet spot a 2” offers for the APS-C sensor.

I’m not interested in revolving filters for my ASI2600MC Pro camera. Been there, done that with other cameras in the past. In fact, all I use is some light pollution filters, a Antlia Quad, and a Svbony duo-narrowband 3nm now. Both work fine for me.

I suppose that if sometime in your future if you ventured into a full-framed sensored camera, the 2” would already be in your possession for the transition. Making doing 2” now more appealing to “future proof” you.

But, it’s your equipment. Do as you’d like.

I did get curious and looked at your proposal. I came across a big NO.

NOT RECOMMENDED Using 36mm in a 2" filter wheel - Search

BlackStarsAstro avatar
BlackStarsAstro avatar

I use a 2600 color and mono. 2in filters fit the sensor just right. any smaller and I would lose a lot of light to the sensor. Unless you like doughnuts around your images, ( no judgement😀), 2in filters are the minimum.

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SonnyE avatar
SonnyE avatar

BlackStarsAstro · Dec 1, 2025, 05:36 PM

I use a 2600 color and mono. 2in filters fit the sensor just right. any smaller and I would lose a lot of light to the sensor. Unless you like doughnuts around your images, ( no judgement😀), 2in filters are the minimum.

I do like donuts around my coffee cup….

Charles Hagen avatar
Charles Hagen avatar

BlackStarsAstro · Dec 1, 2025, 05:36 PM

I use a 2600 color and mono. 2in filters fit the sensor just right. any smaller and I would lose a lot of light to the sensor. Unless you like doughnuts around your images, ( no judgement😀), 2in filters are the minimum.

Where are you getting this from? 36mm filters at the usual distance using a standard IMX571 + Filter wheel combo will not mechanically vignette down to about f/3.5. Unless you are using a particularly fast system, you are in fact losing zero light using 36mm filters on APSC over 2”.

To demonstrate, here’s a master flat taken using 36mm unmounted filters with a QHY268m (same IMX571 sensor) at f/5. The worst corner has 5.7% lower transmission than the center, hardly a donut:

image.png

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SonnyE avatar
SonnyE avatar

Charles Hagen · Dec 8, 2025, 06:57 AM

BlackStarsAstro · Dec 1, 2025, 05:36 PM

I use a 2600 color and mono. 2in filters fit the sensor just right. any smaller and I would lose a lot of light to the sensor. Unless you like doughnuts around your images, ( no judgement😀), 2in filters are the minimum.

Where are you getting this from? 36mm filters at the usual distance using a standard IMX571 + Filter wheel combo will not mechanically vignette down to about f/3.5. Unless you are using a particularly fast system, you are in fact losing zero light using 36mm filters on APSC over 2”.

To demonstrate, here’s a master flat taken using 36mm unmounted filters with a QHY268m (same IMX571 sensor) at f/5. The worst corner has 5.7% lower transmission than the center, hardly a donut:

image.png

Yeah, more like a sheet cake.

I’d like to see more of an end result than a flat.

I don’t know (and never felt it was needed) to compare the filter size Vs: the sensor sizes in the past. But the other day I ran across where a 36mm and 2” filter was being compared. The 2” was something like 44% compared to the 36mm being in the 30ish percentile. Like 44% bigger than a 36mm.

But cameras of days gone by for me had fairly tiny sensors behind even a 1.25”. So, there was a much bigger port to sensor size. For example.

When I got my APS-C sized sensor I could see why I wanted to go with a 2” filter size. I don’t use, and don’t plan to use, multiple filters with my ASI2600MC Pro. I did enough years of experimenting and I’m really happy just fiddling around with light pollution filters now.

My jury is still out about the file’s sizes. Love the images with the APS-C, but the files sure get fat. I didn’t like hours and hours waiting for say PixInsight to trudge through a pile.

But anyway… I guess I like my filters more picture window sized. 😄