IR Blocking Filter for planetary imaging

[Jammy]

I've recently tried some lunar/planetary imaging after some years of DSO imaging and I'm trying to get my head around it all again.

When I tried previously I got some decent (for a beginner) images of the moon, Mars, Jupiter and Saturn using a Philips SPC900nc webcam which I modded for astro.  With this camera I added an IR Blocking filter after removing the Lens.

I'm now trying again, but this time using a QHY5Lii mono guide camera with SharpCap to see if I can get any better images.

My question is do I need to use an IR blocking filter with this camera?  I've tried with and without, and the images (and laptop screen) are far clearer without the filter than with it.

With the filter added everything looks hazey, and I really struggle with focus.  Does a mono camera need an IR Blocking filter?  I'm trying to workout what I'm doing wrong.

Any help would be much appreciated.

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[Owmuchonomy]

It depends upon the near IR sensitivity of your chip.  For example, if the sensitivity is quite good in near IR like it is for both my ZWO cameras (mono and colour) then the best results are when using an IR PASS (not block) filter because those wavelengths passed are less affected by seeing issues.  I find lunar imaging benefits dramatically from the use of a 685nm IR PASS filter.  i can't see any advantage in using an IR block on solar system imaging but I may be missing something.

[Thalestris24]

Hi

I'm not a planetary imager. However, I think it depends on whether you want to pick up IR or not. The problem with not using an IR block with a colour camera is that IR will pass through the bayer matrix/filters and muddy the waters, so to speak. With a mono camera that problem no longer exists - you pick up all wavelengths from UV to IR that the sensor responds to. If you don't want to pick up IR then you may not want to pick up UV either, though maybe it can be advantageous to gather UV from some targets? Presumably, when you mentioned an IR block, you mean a UV-IR block? The IR sensitivity of a qhy5l-ii mono is quite high so blocking IR means the loss of a lot of signal.

Louise

[Owmuchonomy]

This is a lunar shot of mine with a colour ZWO camera and an IR pass filter for example, essentially giving me a high resolution mono image using ALL the pixels.

 

[Jammy]

Thanks for the replies.

Yes I did mean an IR/UV block filter.

I'm waiting for decent weather to try without the filter to see if there is any significant difference, but from your replies I might be better off without the filter.

I'll also look into the Pass filters (I didn't know these existed).  I need to do some reading

[D4N]

Whether you need IR block to get good images will depend on the colour correction in your optics.

If you just have mirrors it should be fine but if you have lenses then the different wavelengths of light can end up at different focal points.  Since the colour correction is mainly aimed at visible light you get get blue bloat from UV and red bloat from IR.  On a mono camera this would just appear as a fuzzy image which is not possible to achieve perfect focus.  The focal ratio also comes into play here, on a fast scope the sweet spot for focus is very small so exacerbates the problem.

Using IR pass as mentioned above gets around the problem in the other direction by blocking everything else so you are just focusing on the IR.

[Jammy]

Thanks Dan, you've made that nice and clear and I now understand.

I have an SCT so may have some fuzziness through the lens.  I still haven't had chance to get the scope out since I first posted this question.

I'm still going to try with and without the UV/IR block and see if there is any major difference.

Thanks again

Jamie

[newbie alert]

Lots of imagers use IR pass in bad seeing conditions

[Uplooker]

On 23/04/2017 at 23:31, D4N said:

Whether you need IR block to get good images will depend on the colour correction in your optics.

If you just have mirrors it should be fine but if you have lenses then the different wavelengths of light can end up at different focal points.  Since the colour correction is mainly aimed at visible light you get get blue bloat from UV and red bloat from IR.  On a mono camera this would just appear as a fuzzy image which is not possible to achieve perfect focus.  The focal ratio also comes into play here, on a fast scope the sweet spot for focus is very small so exacerbates the problem.

Using IR pass as mentioned above gets around the problem in the other direction by blocking everything else so you are just focusing on the IR.

D4N is correct. I am not able to see your signature or equipment you used but if you have any glass in the imaging train, other than mirror, you will need an IR filter as the Red light comes to focus at a different point than the rest. If using a mono camera AFAIK it does not matter