Matching filter size to sensor size

[StuartT]

Am I right in thinking that for an APS-C sensor I would need 2" filters for narrowband imaging?

Thanks

[scotty38]

It depends how far from the sensor the filters are but generally 36mm would usually be sufficient.

[DaveS]

There's a filter suitability tool in the Astronomy Tools suite, but for APS-C, 36 mm should be fine.

[teoria_del_big_bang]

I agree with above replies, I currently use 36 mm filters with my QHY268M, just get camera as close to filter wheel as possible. 

Steve

[StuartT]

Thank you. I didn't even know there was a 36mm size option! I thought filters only came in 1.25 or 2 inch.

Could make a difference in affordability when looking at high quality LRGB or SHO filters, I guess

EDIT: just did a search and the 36mm size seems to be unmounted. Presumably that's ok if you're using a filter wheel?

Edited May 27, 2022 by StuartT

[DaveS]

Yes, filter wheels usually have a 36mm unmounted option. The filters are held in by (Usually) 3 small screws.

[teoria_del_big_bang]

what filter wheel do you have ?
You may need to buy a new carousel for the 36 mm filters but still much cheaper than 3 good NB 2" filters, in fact buying a whole new filter wheel and 36mm filters is far cheaper than 3 new good 2" NB filters 🙂 

Steve  

Edited May 27, 2022 by teoria_del_big_bang

[StuartT]

3 hours ago, teoria_del_big_bang said:

what filter wheel do you have ?
You may need to buy a new carousel for the 36 mm filters but still much cheaper than 3 good NB 2" filters, in fact buying a whole new filter wheel and 36mm filters is far cheaper than 3 new good 2" NB filters 🙂 

Steve  

Hi. I don't have anything yet. I only shoot with OSC. But at some point I plan to become a proper grownup, so I am scoping out what it might all cost me. 

[DaveS]

If you're getting a new camera plus FW, then it might be worth looking at the QHY 268M and the CFW 3 M-US 7x36mm, which has a short connection to the camera, minimising vignetting, and a direct link, reducing the number off USB leads.

[DaveS]

It might also be worth looking at an Antlia filter set, with 3nm Narrow Band. A lot cheaper than Chroma and even more so than Astrodon.

[pipnina]

I am not entirely sure 36mm is quite enough, although its very close. I have a fairly considerable drop in ADU in my flats even after getting the cam as close as possible to the filters (20mm or so? Backfocus built into cam plus filter wheel internals) On a scope (TS Photon F4) that's meant to still be above 90% illumination at the edges of an APS-C sized cam.

The asi EFW retaining rings for the filters does trim a mm or so at least off of the edges of the filter diameter, maybe it has something to do with that.