Anti-alias filter be gone!

[rmuhlack (Richard)]

So I dismantled (again) my modded 1000D in the hope of addressing some star shape issues. In the process I thought I would also remove the anti-alias filter which I (perhaps foolishly) had left in place when I originally did the filter mod.

Well I had some clear skies the following night and thought "what better way to evaluate star shapes than with a globular cluster" - so Omega Centauri it was.

This image consists of 57 x 60secs and 44 x 120sec subs at ISO1600, with a 130mm f5 newtonian on a HEQ5 mount. Processed with Pixinsight

Large version here: http://www.astrobin.com/full/80104/0/

[Still a little left-right elongation which I now suspect is due to the clip on the secondary mirror, as I have seen it with this scope with another camera. Fixing that is on the "to do" list for this weekend. ]

What do you think of the end result?

[nebulosity. (Jo)]

That is absalutly beautiful!

The colours look awesome, and so sharp! Is that a galaxy up to the left? And some galactic cirrus down on the right?

Go dslr

Cheers
Jo

[kosh]

Looks pretty good Richard.

I actually modded my 1000D just yesterday afternoon and didn't really even consider leaving the AA filter out also ( it seems to have gone well btw ).
Can I ask what you are looking to achieve by leaving it out?

Cheers,
Goran.

[RickS (Rick)]

Richard,

Do you have a "before" image to compare? It's fairly minor but the stars don't look quite perfect to my eyes at full resolution, even close to the centre of the image. Overall a nice job though...

Cheers,
Rick.

[Merlin66 (Ken)]

Richard et al,
Removing both the colour balance filter (the usual mod) and the front dust shake/ AA filter removes all the UV-IR cut off.
The sensor now gets a full spectrum hit and based on spectroscopic measures can record from 360nm in the UV right through into the NIR.
Great for spectroscopy but can lead to star bloat in astrophotography ( excess UV and /or excess IR). Obviously less of a problem in fully reflective scopes which bring all wavelengths to a common focus.

[kosh]

Originally Posted by Merlin66

Richard et al,
Removing both the colour balance filter (the usual mod) and the front dust shake/ AA filter removes all the UV-IR cut off.
The sensor now gets a full spectrum hit and based on spectroscopic measures can record from 360nm in the UV right through into the NIR.
Great for spectroscopy but can lead to star bloat in astrophotography ( excess UV and /or excess IR). Obviously less of a problem in fully reflective scopes which bring all wavelengths to a common focus.

So ken, you think leaving the front AA/dust filter on will actually help reduce the star bloat when using with my ED80 or is removing the IR filter enough to cause this?

[rcheshire (Rowland)]

Lovely work Richard. All DSLR conversions should have the AA filter removed. A UV/IR filter is needed if using refractors. Easy EOS conversion, is to remove both factory filters and fit an Astronomik UV/IR Clip-in filter. If you then use or alternate between reflecting and refracting scopes you have the best of both worlds. I tested AF on a 1000D and it works in this configuration.

[rmuhlack (Richard)]

thanks all for the feedback

Ken - I should have been more specific in that I have replaced the stock canon UVIR filter with an Astrodon Inside Luminance filter (see here).

When I first modded the camera I kept the anti alias filter in place, however I have subsequently decided that this was contributing to excessive FWHM values, and so when I had the camera disassembled on the weekend I decided to remove that filter as UVIR filtering was provided by the astrodon.

RIck - I agree the stars are still not perfect, but I am thinking (hoping?) that this is now related to an overly tight clamp on my secondary mirror rather than with the camera (especially since I did not see this when using this camera on my VC200L). Am planning some further investigation over the next few days.

[rmuhlack (Richard)]

Originally Posted by RickS

Richard,

Do you have a "before" image to compare?

Cheers,
Rick.

unfortunately I dont have a "before" image of the same target, however these (full size) images were taken with the camera after the initial mod, so with the Astrodon UVIR filter and before the removal of the anti alias filter and with the same scope, coma corrector and mount:

The "Wolf" Nebula: http://www.astrobin.com/full/55454/C/?real=&mod=
NGC300: http://www.astrobin.com/full/59651/B/?real=&mod=

[alpal]

Originally Posted by rmuhlack

So I dismantled (again) my modded 1000D in the hope of addressing some star shape issues. In the process I thought I would also remove the anti-alias filter which I (perhaps foolishly) had left in place when I originally did the filter mod.

Well I had some clear skies the following night and thought "what better way to evaluate star shapes than with a globular cluster" - so Omega Centauri it was.

This image consists of 57 x 60secs and 44 x 120sec subs at ISO1600, with a 130mm f5 newtonian on a HEQ5 mount. Processed with Pixinsight

Large version here: http://www.astrobin.com/full/80104/0/

[Still a little left-right elongation which I now suspect is due to the clip on the secondary mirror, as I have seen it with this scope with another camera. Fixing that is on the "to do" list for this weekend. ]

What do you think of the end result?

Hi Richard,
The end result is great.
I probably would have tried to stretch the core more
to stop it being all one brightness.

cheers
Allan

[RickS (Rick)]

Originally Posted by rmuhlack

RIck - I agree the stars are still not perfect, but I am thinking (hoping?) that this is now related to an overly tight clamp on my secondary mirror rather than with the camera (especially since I did not see this when using this camera on my VC200L). Am planning some further investigation over the next few days.

A good chance of that, I think, given the star shapes. Good luck with the investigation, Richard!

[atalas]

I think It turned out very nice!well done.

[strongmanmike (Michael)]

Despite the issues you have mentioned...that's a great Omega Richard! Love the golden orb look, Omega should be bright across the centre so nice job

Mike

[cosmophoton (Luiz)]

Really good, Omega Centauri is a tough test. I liked the core brightness too, it seems well balanced to me.
Cheers,
Luiz Duczmal