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Old 27-09-2020, 11:54 AM
SB (Chris)
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Help with IR Pass Imaging

Hi Everyone,
Last night I had a go at using the Astronomik ProPlanet 742 IR Pass Filter.

I used the ASIAIR focus software and got the FHD down to 3.1. However I note that there are halos round the stars in the camera FITS images.

Is this normal or am I missing something? I also used a Duo band filter (pre and post using the IR Pass filter last night) and these images were fine (which would tend to exclude imaging train problems).

See attached image of Tarantula Nebula (Esprit 100, ASI183 MCP, Astronomik ProPlanet 742 IR Pass Filter).

Many thanks

Chris.
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Old 27-09-2020, 01:57 PM
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multiweb (Marc)
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You do tend to get halos on brighter stars in IR. Focus is critical. Some refractors more than others will show bloating in the stars. Others not. I had a triplet APO that was bloating stars and showed diffraction artefacts around the lens clips. The FSQ106N I got later on showed pristine stars in IR. It might be the fluorite or the refractive indexes of the various lenses are different or the way it handles color correction. Reflectors with mirrors only and no glass in the imaging train are less susceptible to halos in my experience. I can't comment on the tarantula. Never imaged it in IR.
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Old 28-09-2020, 07:31 AM
SB (Chris)
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You do tend to get halos on brighter stars in IR. Focus is critical. Some refractors more than others will show bloating in the stars. Others not. I had a triplet APO that was bloating stars and showed diffraction artefacts around the lens clips. The FSQ106N I got later on showed pristine stars in IR. It might be the fluorite or the refractive indexes of the various lenses are different or the way it handles color correction. Reflectors with mirrors only and no glass in the imaging train are less susceptible to halos in my experience. I can't comment on the tarantula. Never imaged it in IR.
Thanks Marc,
Here is another image of the Orion Core (2 x 10 min exposures) taken with the IR Pass filter. Stars appear a little tighter this time.

Chris
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Old 28-09-2020, 10:07 AM
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Spherochromatism is likely once you go outside the design spectrum of a refractor....and near I/R would place you there with many telescopes.

As Marc pointed out, more exotic telescopes are usually less affected.

The problem will disappear with a well corrected reflector.
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Old 28-09-2020, 10:24 AM
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Thanks Marc,
Here is another image of the Orion Core (2 x 10 min exposures) taken with the IR Pass filter. Stars appear a little tighter this time.

Chris
Here's a couple of comparisons for you to illustrate what I was talking about. Let me know if you are having problems viewing the links. I'm using the same filter as yours. Astronomik Pro Planet 742nm.

Triplet APO (Triplet FPL53) Notice the clips diffractions

FSQ106N (fluorite quadruplet)

CN-212 (classical cassegrain - no glass)
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Old 28-09-2020, 10:38 AM
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Here's another couple in Orion with the FSQ106N (fluorite quadruplet)

M42

and

Horse Head

C11
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Old 28-09-2020, 12:36 PM
SB (Chris)
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Hi Marc,
Thanks for these comparisons - much appreciated.

How did you manage to get colour in the the C11 and Horsehead images (were they combined with visible spectrum images)

Chris
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Old 28-09-2020, 12:40 PM
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Hi Marc,
Thanks for these comparisons - much appreciated.

How did you manage to get colour in the the C11 and Horsehead images (were they combined with visible spectrum images)

Chris
You do a blend 50/50 with a straight LUM. IR IRLUM LUM or LUM IRLUM IR so you get a bicolor picture.

Sii/IR in the same process can be pretty groovy too. Experiment with different DSOs.

M8

Corona Australis (IR/LUM)
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Old 02-10-2020, 06:35 AM
SB (Chris)
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Hi Marc,
Following your suggestions I tried a combo of IR and Visible on Orion core (attached). Looks like some potential to explore this further.

Chris.
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Old 02-10-2020, 02:34 PM
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Hi Marc,
Following your suggestions I tried a combo of IR and Visible on Orion core (attached). Looks like some potential to explore this further.

Chris.
That's pretty cool. Nice image scale. If you can tame the exposures for the trap you'll have a corker. You should try the hourglass in M8 or th Homunculus in Carina. That's on my todo list. Another good one is the bug nebula. It's not far from the cat paws.
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Old 05-10-2020, 11:46 AM
SB (Chris)
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Hi Marc,
I attempted the merge with the full image.

Chris
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Old 05-10-2020, 01:44 PM
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That looks good.
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