'IR Filtering' A Toucam - The Good and The Bad

[ballaratdragons (Ken)]

Last night, apart from imaging Globs and Opens with the Toucam, I did an IR filter comparison test.

I imaged Trifid, Eagle, and NGC4945 with the IR Filter, then removed the filter and imaged them again.

The below comparisons all had exactly the same settings during capture. Both Trifids have matching settings, both Eagles match etc.

I have not processed any of these images so you can see how they look raw. They come warts and all. Well . . . hot pixels and all.

Both ways have their benefits. Filtered gives far better stars and background, but Unfiltered gives better Nebula and Galaxy.

Make what you want from this comparison test. I just thought I'd share the results.

1. Trifid
2. Eagle
3. NGC4945

[duncan]

Hi Ken,
Trifid and NGC4945 look better to me with IR filter. Seems to show crisper detail on the dark lanes. I guess some objects are better to use it on than others.
Cheers
Ps All lovely shots anyway.

[monoxide]

interesting, with the IR filter in the detail looks a lot better in trifid/ngc4945
eg. it looks more structured.
mabee try longer exposures with the IR filter in place?

[ballaratdragons (Ken)]

Originally Posted by monoxide

interesting, with the IR filter in the detail looks a lot better in trifid/ngc4945
eg. it looks more structured.
mabee try longer exposures with the IR filter in place?

I can't do longer exposures with the filter in. The Amp glow takes over the whole image, I tried.

[[1ponders] (Paul)]

Nice triffid.

As a guess I'd say the IR filter is like the one in the 300D. It intrudes into the red part of the spectrum too far. Way too far by the look of it. Have you ever tried you camera with a "proper" IR filter Ken?

[bojan]

Hi Ken,
those "bloated" stars, ithey seem as if the part of spectrum which is not blocked by IR filter is not focussed properly... what kind of optic do you use? it is not reflector, or is it? I suppose those pics are independently focussed....

[ballaratdragons (Ken)]

Originally Posted by [1ponders]

Nice triffid.

As a guess I'd say the IR filter is like the one in the 300D. It intrudes into the red part of the spectrum too far. Way too far by the look of it. Have you ever tried you camera with a "proper" IR filter Ken?

Nope Paul, they are too expensive. This was just a trial after the idea of using the Toucams original IR lens plopped into the adaptor was posted in here.

Originally Posted by bojan

Hi Ken,
those "bloated" stars, ithey seem as if the part of spectrum which is not blocked by IR filter is not focussed properly... what kind of optic do you use? it is not reflector, or is it? I suppose those pics are independently focussed....

I used an ED80 and .65 focal Reducer

Individually focused? I don't get the question unless you mean did I re-focus on each object. No I didn't, focus was perfect on each one so I didn't have to re-focus. I always check focus on each object. The only time I had to re-focus was after taking the IR filter out.

Also, none of the images above have been processed yet. Just raw data stacked. I usually clean the stars up during processing.

[monoxide]

you could always try a bintel IR filter and see if theres any noticable difference, $29 and heres what it says

'This filter has an extremely sharp cutoff at 690nm yet leaves all the visible red, including the important 656nm H-alpha emission line, preventing IR wavelengths from blurring fine detail in your digital images. Recommended For Use With CCD, Video & WebCams for sharper images Works with any CCD camera, eyepiece, or adapter that accepts 1.25" cells.'

[bojan]

Originally Posted by ballaratdragons

I used an ED80 and .65 focal Reducer

Individually focused? I don't get the question unless you mean did I re-focus on each object.

I meant refocus after taking IR filter out.
It seems this system has trouble with focus in deeper IR, that became obvious without IR filter. ?

[ballaratdragons (Ken)]

Originally Posted by bojan

I meant refocus after taking IR filter out.
It seems this system has trouble with focus in deeper IR, that became obvious without IR filter. ?

It isn't focus, it's Halo's around the stars.

Here is the same Unfiltered image before and after processing. It helps to remove the Halos.

Oh, and add spikes in the next pic

[bojan]

Well, halo of this nature is usually the consequence of spherical aberation or internal reflections in the optical system.
It seems to me the latter may be the case, the focal reducer being not properly corrected or coated for IR part of the spectrum, and the fault becomes visible when you removed the IR filter.

[Terry B]

Originally Posted by ballaratdragons

It isn't focus, it's Halo's around the stars.

Here is the same Unfiltered image before and after processing. It helps to remove the Halos.

Oh, and add spikes in the next pic

The halo is probably because you are using a refractor. The IR is not corrected like the visible light. This is why older SLR lenses had a IR focus adjustment when you use IR film. I would think that if you use a reflector that focuses all wavelengths at the same spot the IR halo should disappear. I have tried this with my VC200L. I put a near IR filter in and took pics with my CCD and the focus is the same as visible light.

[ballaratdragons (Ken)]

Originally Posted by Terry B

The halo is probably because you are using a refractor. The IR is not corrected like the visible light. This is why older SLR lenses had a IR focus adjustment when you use IR film. I would think that if you use a reflector that focuses all wavelengths at the same spot the IR halo should disappear. I have tried this with my VC200L. I put a near IR filter in and took pics with my CCD and the focus is the same as visible light.

Interesting.
But the halo's are in the pics without the IR filter.

I won't be able to use my 12" reflector for a while yet as I have to make the whole thing more lightweight. There is no way I'm putting it on my EQ6 at the weight it's at now. Yeah, I know, others do, but I can't afford to repair a strained mount.

So I'll just keep plodding along with the set-up I'm using now. I'm having fun and that's the main thing

[Terry B]

Originally Posted by ballaratdragons

Interesting.
But the halo's are in the pics without the IR filter.

I won't be able to use my 12" reflector for a while yet as I have to make the whole thing more lightweight. There is no way I'm putting it on my EQ6 at the weight it's at now. Yeah, I know, others do, but I can't afford to repair a strained mount.

So I'll just keep plodding along with the set-up I'm using now. I'm having fun and that's the main thing

Yes. That is correct. When the IR filter is in place no out of focus IR is getting to the sensor so there should be no halo.

[ballaratdragons (Ken)]

Originally Posted by Terry B

Yes. That is correct. When the IR filter is in place no out of focus IR is getting to the sensor so there should be no halo.

Inerestingly, only the Orange stars give an obvious 'Halo' shape. White stars are just a bloated mess.

[Terry B]

Do the orange stars emit more IR? I don't know. Assuming black body radiation they should.