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Old 26-11-2020, 05:15 PM
TrevorW
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HALO around stars

I recently did some images using my ED80 and I notice HALO around the bright stars now this effect was not present in frames I took using the ED115 however the camera setup was the same as well as exposure length. I use a IR cut filter in the camera chain when taking both images - any clues as to what may cause the HALO, thanks


1st image TUC 115ED no halos
2nd image NGC1985, 80ED halos
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Old 26-11-2020, 06:09 PM
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I may not be 100% right but it seems to me to be imaging through condensation of sorts, just MHO.

Leon
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Old 26-11-2020, 06:38 PM
TrevorW
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Quite a warm night here last night still 22 at 8; but max only 29 yesterday with RH of 44 so I'm not sure of condensation unless I had camera temp set to low, ??
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Old 26-11-2020, 07:44 PM
glend (Glen)
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Quote:
Originally Posted by TrevorW View Post
Quite a warm night here last night still 22 at 8; but max only 29 yesterday with RH of 44 so I'm not sure of condensation unless I had camera temp set to low, ??
Ok, you mentioned camera temp, that could be a telling factor. So now we can assume your running a cooled camera, which opens up condensation possibilities. There is no such thing as " having the camera temp set too low", if the system is functioning correctly. What camera is it? Does it contain dessicant in the sensor chamber? Are the seals good? Etc
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Old 26-11-2020, 07:53 PM
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Ok, you mentioned camera temp, that could be a telling factor. So now we can assume your running a cooled camera, which opens up condensation possibilities. There is no such thing as " having the camera temp set too low", if the system is functioning correctly. What camera is it? Does it contain dessicant in the sensor chamber? Are the seals good? Etc



QHY 183c, brand new
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Old 26-11-2020, 07:59 PM
Startrek (Martin)
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The latest ZWO cooled OSC cameras have a 5W polyimide anti dew heater around the protective window to eliminate condensation, dew etc.., at all sensor temperatures
I have the 2600MC and by default I leave the dew heater on as I have a dedicated 12V 7.5A power supply to the camera
QHY usually piggy back ZWO ( and visa versa )so if your camera is a current model then itís possible it has an anti dew heater installed
Just check their website or your suppliers site
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Old 26-11-2020, 08:08 PM
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Yes I believe it does thanks
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Old 26-11-2020, 09:28 PM
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My suggestion would be colour correction. The IMX183 chip is a high QE with small pixels. Was your 115mm a triplet? The ED80 is only a doublet and that may be the cause.
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Old 26-11-2020, 09:31 PM
TrevorW
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The 115 is an Orion EON is also a doublet have taken images with different camera using the ED80 which is a Stellarvue, I have noticed halos before but not in all images

Last edited by TrevorW; 26-11-2020 at 10:47 PM.
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Old 27-11-2020, 07:35 AM
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There is some chromatic aberration and it is exacerbated by the filter you are using and the exposure length some noticeable star bloat as well. All these add up to halos. The filter needs to be as close to the sensor as possible in the imaging chain.
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Old 27-11-2020, 08:35 AM
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They look like dew on something, the camera or the scope lens.
Possibly a reflection but they look more definite.

As others mentioned expect ASI183 with its small pixels and probably greater sensitivity in the blue to highlight chromatic aberration and other aberrations more clearly.

But lets go with the dew premise first.

Greg.
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Old 27-11-2020, 12:35 PM
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Looks like sphero-chromatism to me.

Try using a UV/IR block filter. If the filter makes the halos far less visible then it's QED.
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Old 27-11-2020, 05:21 PM
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The QHy183c has a built in IR coating on the optics window I added another filter in the image train so I'm wondering if this may have caused the issue
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Old 06-12-2020, 12:45 PM
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Quote:
Originally Posted by TrevorW View Post
The QHy183c has a built in IR coating on the optics window I added another filter in the image train so I'm wondering if this may have caused the issue
I/R is unlikely to be the problem...the Blue/UV end is more commonly under corrected.
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Old 06-12-2020, 01:08 PM
TrevorW
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Thanks
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Old 06-12-2020, 01:57 PM
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I've read that the QHY183C has IR cut but not UV, so you'll want to use a UV-IR cut filter in front of it.
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