Doesn't look like AA filters have been discussed in the astrophotography group. It would SEEM that no AA filter or a weak AA filter would be a PLUS for astrophotography (no moire worries THERE).

We all probably know that the Pentax K-5 IIs has no AA (anti-alias) filter, meaning sharper images (but for some subjects a risk of moire). You probably also know that the K-3 has no AA filter but can simulate one with two different levels of vibration to the sensor.

But what I did NOT know what that Pentax was toying with the idea of eliminating the AA filter in earlier models. The K-01 and the K-30 are both said to have WEAK AA filters (a bonus for astrophotography).

More info: Moire from K-01: Pentax SLR Talk Forum: Digital Photography Review, www.pentaxforums.com/forums/138-pentax-k-01/181891-k-01-h..., and www.pentaxforums.com/forums/138-pentax-k-01/205516-k01-ha....

With K-01 bodies still available at around $250, I think they represent the greatest bang-for the buck value for astrophotography. It represents the lowest cost way to get all of the following:

lowest cost way to get:

+ the stunning Sony 16MP APS-C sensor that performs so well at high ISOs (in fact, it has been described as ISO-LESS)

+ mirrorless (no mirror flop to deal with)

+ built-in intervalometer

+ lighter weight than most DSLRs

+ perhaps most importantly: Live View with Focus Peaking (superb for precise focusing in astrophotography)

+ Easily uses any K-mount or m42 lens, or telescope with adapter

+ AND a weak AA filter for super-sharp IQ

Does anyone have any Real World examples to share or opinions on how this might be a real plus for AP?

When Cloudynights forum gets back online we can check some threads about the Canon AA filter removal efforts. Several users have been pleased with the results for astro work.

I know that Nightfly has been using a K01.

The mirrorless option is very interesting for the purposes of keeping it simple and to reduce vignette on fast optical systems.

Another advantage over the K3 is larger pixels = more light gathering capability.

Of course, if I were to get one, I'd have the IR filter replaced and then open it up to see where I can put a peltier cooler.

Removal of AA filter has nothing to do with IR-block filter that is still there,so you don't get noticeably better sensitivity for emission nebulae (they emit in IR and red part of spectra). I've already tried it and for my K-3 it's no significantly better than on my old K-7 in the sence of sensitivity for that part of spectra. Only reduced noise of course and higher resolution...overall better image quality.

I want to buy in time some old K-5 and let the IR filter remove - body only for astrophotography and IR photoraphy purposes...

You removed the IR filter from the K3 and there was no improvement in Ha response?? That's surprising! If you still have the old IR filter it would be interesting to get a spectral transmission graph done to see if Pentax quietly chose glass that was good for astronomy work.

No off course I did not remove the filter! Just that absence of AA filter in K-3 do not affect gain in Ha (I also think it should be noticable - but it appears that AA filter do not absorb noticable portion of IR wavelenghts). I am not that rich to modify brand new body :-D I plan buying old K-5 for this modification.

You can do that right now, thanks to the Google cache. Just do your search (adding the advanced operator "site:cloudynights.com"). Then click the little "down arrow" icon next to the URL. Choose "Cache". Bob's your uncle.

The K-01 doesn't give you that (usual) mirrorless advantage. It maintains the same flange to sensor distance as mirrored Pentax DSLRs. The focal length multiplier is the same as other Pentax APS-C cameras also.

Well it is not simply about AA-filter - but all filters in front of the sensor, but i didn't want to start a new thread so here it is.

I bought K-30 and got it modified - replacing of sensor filter with pure-glass so the camera can be used for astrophotography (with UV-IR-cut or LPS filter) and IR-photography.
So i kept the original filter and i measured its transmitance at work. Here is the graph:



And here is comparison with Hutech IDAS P2 light pollution supression filter (lens front filter thread).



Sadly i do not have sample of new sensor "glass", so no comparison here

Delete this message please - it was duplicate of former message

I had a Canon T1i (500d) that I had the AA filter removed from (by maxmax.com) that I used for astrophotography. I recently sold it. Anyhow, the it performed much better for astro than the stock version. It had a replacement (non-AA IR filter put in, so it was still usable for daytime photos and so that the autofocus would still work right.

Recently got a K-01, and am looking forward to popping it on the scope at the next opportunity to see how it does. Sure is nice not having mirror flop (or waiting for mirror lockup) but I do wish it would accept a wired remote.

In my experience, obtaining focus with focus peaking is not as accurate as using a Bahtinov mask on a 1st magnitude or brighter star.

Jack

Good to know!

That's my experience too. Focus Peaking can fool you into thinking you've reached critical focus before you actually have.

Just another point on the AA filter. Stephane Poirier: Accueil / Albums / Astrophoto / Ciel Profond | PhotosSteph is a Pentax astrophotography "hero" of mine. He states that the atmosphere is enough of an AA filter (in itself) and therefore none is needed on the camera. This makes the Pentax K-5 iis and the K-3 the best in that regard.

Has Pentax made it possible to shoot the buiit-in intervalometer in "mirror-up"/self-timer mode yet? If not, would it not be possible to set up an external intervalometer with the camera set to a self-timer mode to allow time for vibrations to subside before the shutter trips?

If you are referring to astronomical seeing, the effect would be most pronounced using longer focal length lenses, but perhaps negligible in wide angle lenses. I shoot the K-5IIs with wide lenses, mostly the Samyang 16mm f/2, and at pixel peeping level I recover many solidly red, green, and blue stars that are apparently due to the absent AA filter. The green appearing as the most unnatural of course. I do not recall seeing these on my K-01. Even star trail images reveal a rainbow trail as the star images move across the photosites. The effect is hardly noticeable on small images, but my be an issue on crops and/or large prints.

The region around Altair / Tarazed - K-5IIs 16mm Samyang @ 3.2 90 seconds ISO 1600 - Actual pixels.

Have you eliminated the cause of these as hot pixels due to long exposure + high ISO? For example, if you make a "dark" frame (take identical exposure with lens covered up so it receives no light) do you get the same colored dots?

1. Using an external trigger/intervalometer with a K-50 it is absolutely possible with exposures under 30 seconds by setting the body drive mode to '2 second timer' which pops the mirror up 2 seconds before the shutter releases.
2. Can't wait for a chance to try my new K-01 for this. It's itching for some deserved scope time.