Anti-aliasing filter removal?

[Beardy Bob]

I have read some good things about increases in image sharpness in modern DSLRs gained by removing the anti-aliasing filter (and replacing with a standard Baader filter to cut UV/IR).

The theory looks sound to me, but as with anything the proof is in the pudding! Has anyone used a DSLR with the anti-aliasing filter removed?

[Merlin66]

My 1000D has both filters removed - I use a Astronomik MC (clear) clip in to allow the use of standard camera lens.

I don't know about image sharpness but it definitely works 100%

[Beardy Bob]

Thanks Merlin. Sounds like you'll be benefiting from not having an AA filter, but like you say, if you've never used the camera BEFORE removing the AA filter then it's difficult to say what difference, if any, it's making.

Also, I'm a little confused as to which filter does what in the more modern Canon DSLRs. Old Canon DSLRs (like the 350d) needed a replacement (Baader) filter to stop star bloating from IR once the original filter had been removed, but from what I understand the newer ones (like the 1100d-not sure about the 1000d) only need one of the filters removing and don't need a replacement to cut out IR/UV as long as you leave the second filter in place. It would seem that it is this second filter that is acting as the AA filter as well as a UV and/or IR cut. Can anyone who knows their way around the insides of these things enlighten me?

Interestingly, Nikon have released a special camera with the AA filter removed (seemingly at a large mark-up of course!) and the results look brilliant:

http://www.lifepixel.com/blog/anti-aliasing-low-pass-filter-removal

..and quite a few Canon owners seem to have latched onto the idea. Here's one example that I quickly googled. Again, the results make you wonder why the filter is there in the first place! :

http://www.canonwatch.com/eos-5d-mark-iii-hacked-anti-aliasing-filter-removed-more-sharpness/

I was hoping someone on here could share some real astro shots from before and after AA filter removal (and of course what exactly the AA filter is!).

[Merlin66]

In the current Canon camera there are two filter elements, both about 0.8mm thick.

The one at the sensor cover is the colour correction filter which supresses the red response. This is the filter element removed in most astro mods. It's removal allows more red light to hit the sensor and give about a 50% increase in Ha response.

It is possible to achieve "acceptable" focus with standard lens without adding any other secondary filters.

The second element "dust shake/ anti-alias" filter is at the front of the camera and is actually a UV-IR blocking filter. If this is removed then the whole QE curve of the CCD chip is used and gives effective coverage from 370nm to NIR.

As mentioned, the removal of both filters (total thickness =1.6mm) requires at least a MC clip in filter to re-establish focus.

I'd think, if ONLY the dust/anti-alias filter is removed, like the astro mod, standard lens should still work.

The attached transmission curves show the effects of each filter element. Filter #1 is the anti-alias, Filter #2 the colour correction

Hope this helps......

Canon front filter test.pdf

[StuartJPP]

Gary Honis has done some tests with and without the front filter present (I.e. the anti-alias filter).

The AA filter comes in handy for daytime photography and helps to eliminate moire however it serves no purpose for astro work that I know of.

I'm not sure how it would affect DSO imaging, can only help I'd suspect but should certainly make a difference to planetary imaging using crop mode.

Note that removing the AA filter (or any filter) may not allow infinity focus on some lenses. Additionally you would want some filter with a refractor or lens to prevent star bloat.

Gary's report...

http://ghonis2.ho8.com/FullSpectrum/FullSpectrum.html

[Beardy Bob]

Thanks, yes, that clears up what the two filters do. I was thinking exactly the same about planetary imaging too. It should certainly help capture all those small details when cropped right in running at 24fps in the newer models with video capture.

I'd love to see what difference it makes, but unfortunately I don't have the nerve to buy a new model DSLR and mod it, or the cash to buy one modded and one not to compare!

[Xlracer]

Have a look at Andy Ellis's excellent article here http://www.astronomiser.co.uk/eosmod.htm

[Beardy Bob]

Thanks xlacer. A lot of people have referenced that website before so I'd already read that article before I asked the question on here. I don't think he mentions AA filters at all, but seeing as there's little need to remove the second filter in most astro-mods (which is the one that seems to be acting as the AA filter too - thanks Merlin!) I guess that's why no-one has a real comparison to show what difference it makes to astro photos.