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  #1  
Old 05-01-2019, 11:34 AM
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that_guy (Tony)
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Issue with LRGB combine

Hi guys, I've just come back from a full night of "imaging" at Wyaralong and I've noticed that when I combine my RGB sets, the image comes out super monochromatic and with ALOT of saturation I can see a bit of violet. My question is, did my filterwheel die at somepoint and not change filters (hence the monochromatic imgae?) when I linked screen transform the RGB combined image, the image came out super green but once I colour calibrate and background neutralise, it comes out almost monochromatic. The only reason I can think of that it ISNT a filterwheel issue is that SGP wouldnt start the new filter sequence if the filter didnt change correctly.
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  #2  
Old 05-01-2019, 11:44 AM
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SGP does generate an error message if it can't select the designated filter. It won't proceed with the sequence, stopping. Check your SGP log file to be sure.
I have no idea what processing your talking about.
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  #3  
Old 05-01-2019, 11:53 AM
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Do the raw mono images through the "different filters" look different?
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  #4  
Old 05-01-2019, 11:55 AM
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I'd do a careful comparison of a small area of an example from each filter and look at the stats (e.g. median value) and you should be able to make an educated guess whether they were each taken with a different filter. It's even easier if you have some colourful nebs or galaxies in the field. Might be worth checking the FITS headers as well in case there are some hints in there.
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Old 05-01-2019, 11:55 AM
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I'll post a screen grab of auto stretched stacked of the RGB. I have a feeling they look identical.
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Old 05-01-2019, 11:59 AM
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If you're getting a green cast with a linked stretch then it seems unlikely that they can all be identical though I guess it's possible if some (green) subs are brighter than the others due to cloud.
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Old 05-01-2019, 12:06 PM
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Quote:
Originally Posted by RickS View Post
I'd do a careful comparison of a small area of an example from each filter and look at the stats (e.g. median value) and you should be able to make an educated guess whether they were each taken with a different filter. It's even easier if you have some colourful nebs or galaxies in the field. Might be worth checking the FITS headers as well in case there are some hints in there.
Ive checked the fits header for what its worth, they all seem to have the correct corresponding filters. This is what the images look like with STF

1. R
2. G
3. B
4. RGB Linked STF
5. RGB Unlinked STF
Attached Thumbnails
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Click for full-size image (b.jpg)
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Old 05-01-2019, 12:09 PM
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Have you tried a RGB combine of one individual sub of each? There does seem to be some variation between the three subs.
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Old 05-01-2019, 12:15 PM
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Ive just tried a bunch of different subs and with the same results. i've also checked some of the R subs side by side with some of the G and they look almost identical. I'm beginning to suspect filterwheel :/ I miss imaging with a colour camera aha
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Old 05-01-2019, 12:49 PM
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That's a shame! The B3Estimator process will let you generate one synthetic colour if you have the other two.
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Old 05-01-2019, 01:18 PM
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I think I know what happened, I have to thread the QHY to the ZWO miniEFW perfectly otherwise the filter will catch sometimes on the male thread. When I took it apart to replace the narrowband filters with the RGB, I mustve threaded it in too deep. Oh well! You learn from these experiences aha.

Another quick question. I have access to a QHY8L from the club on loan, would I have any issues using this for the RGB and combining them with narrowband data from the QHY9? I don't want to deal with filterwheels at my limited time out at a dark sight. At home I can spend all the time in the world mucking about with the filter wheel aha.
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Old 05-01-2019, 01:35 PM
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Another quick question. I have access to a QHY8L from the club on loan, would I have any issues using this for the RGB and combining them with narrowband data from the QHY9?
Yes, that should work. Your FOV will be the smaller of the two but you'll be able to register the colour data to a NB registration reference sub then integrate and combine the RGB master with the NB masters.
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Old 05-01-2019, 01:37 PM
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They're both the same sensor size so they should have the same FOV.
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Old 05-01-2019, 01:59 PM
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They're both the same sensor size so they should have the same FOV.
I couldn't remember offhand. I think the QHY8L pixels are a little bigger but that will be fine.
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  #15  
Old 05-01-2019, 07:16 PM
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Sorry to be pedantic, but those camera CCD chips are not the same size.

QHY8L has a 25.1mm x 17.64mm chip, with 7.8 micron pixels and an array of 3032 x 2016 pixels.

QHY9 has a 17.9mm x 13.5mm chip, with 5.4 micron pixels and an array of 3358 x 2536 pixels.

So you will be limited by the FOV of the QHY9.

Cheers
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  #16  
Old 06-01-2019, 12:21 AM
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yup, you're right, i was getting confused. Limited to the QHY9 FOV doesnt bother me since thats what I was imaging with anyways aha.
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