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Old 03-12-2020, 08:49 PM
TrevorW
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QHY 183c see darks

I'm used to use a QHY 8 CCD camera and when you created darks they were dark in fact with that camera you didn't really need darks, however I notice with the CMOS 183c darks are not dark dark and there appears to be amp glow on the right side of the image, has anyone experience with this camera etc or am I do something wrong, the darks are set with gain either 0 or 9 offset 30 exposure 180s, either gain nsetting the amp glow still appears.
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Old 03-12-2020, 09:49 PM
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By the way the 183C is a QHY camera. QHY is the brand. CMOS is a the type of sensor. The other main manufacturer is ZWO (their main competitor although I see SBIG is offering a mainstream CMOS camera to compete.

All these CMOS cameras except a few of the latest suffer amp glow. It shows up a light streak on the side of the image.

Amp glow disappears with the correct dark exposure. A master dark is several dark exposures at the same temperature, the same gain and the same offset and same exposure duration as the light exposures.

So its usually easiest to use one or two different settings and a temperature that you can achieve all year round and at around 85% power. That probably is around -10C for the 183C.

Exposure lengths may be 60 seconds to 500 seconds and possible longer if you do narrowband - 10minutes.

So make a dark library of say 12 x 60 seconds -10C and at one gain and offset (I don't think you need to change the offset, keep it the same for all).

Create the master dark using a program that will do that.

Make another at the next most used exposure times the same way, say 2 minutes (120 seconds) then 5 minutes.

The 183 you just use darks not biases and also use flats. Flats are another procedure. They get rid of vignetting and uneven illumination as well as dust donut shadows in images.

Amp glow can sometimes be not very noticeable if the signal is strong in the light exposures and it is more noticeable in dimmer images with longer exposures. 30 second exposures may not show much amp glow at all.

Dealing with amp glow in CMOS cameras is just something you need to be able to do. Its not really any different to CCD cameras which also need dark exposures. But CCD's do not have amp glow. But then neither do several latest model CMOS cameras like the 533, 2600, 410, 2600 and 6200 cameras (ZWO ASI numberings).

Greg
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Old 04-12-2020, 12:53 AM
TrevorW
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Thanks Greg


What setting for gain and offset while imaging I've tried 8 and 54 also 10 and 30 any preference here, also can the darks be shorter exposure length than the lights etc with the QHY8 I didn't really need to worry about darks that much, also those ZWO ASI numbers any idea to QHY equivalents-
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Old 04-12-2020, 08:04 AM
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The darks need to be the same settings as the lights, right down to exposure time, but you do not need to shoot the darks at the same time as you are shooting the lights. With a cooled camera you can shoot a library of darks at the various settings you will use for acquiring lights, preferably around 50 of each exposure/gain/temp combination you can use (As Greg posted, best is to use a temperature the cooler can maintain all year) then create a master dark for each scenario (As in 60 seconds -10 degrees, lowest gain, 120 Seconds, 300 seconds etc) which you can then apply to the appropriate lights.
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Old 04-12-2020, 08:35 PM
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Quote:
Originally Posted by TrevorW View Post
Thanks Greg


What setting for gain and offset while imaging I've tried 8 and 54 also 10 and 30 any preference here, also can the darks be shorter exposure length than the lights etc with the QHY8 I didn't really need to worry about darks that much, also those ZWO ASI numbers any idea to QHY equivalents-
I had a ZWO ASI183M pro. That was 53 and 111. Gain numbers are different for QHY for some reason. Unity gain is one target. That's the point where 1 ADU = 1 electron.

Greg.
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Old 04-12-2020, 10:04 PM
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Trevor, as Greg says the gain values are different on the QHY from the ZWO.

Useful gain values might be 5, for maximum dynamic range (if you’re imaging at a dark site) and 11, which is unity gain. Maybe 20 for narrowband, but the DR gets a bit thin up at that gain.

Folk seem to use offset 30 with the QHY, although I’m uncertain of the maths behind that.
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Old 05-12-2020, 07:04 AM
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You might have to suffer through some theory here.

https://www.qhyccd.com/index.php?m=c...atid=23&id=226

I think in practice though you will simply pick a mode that matches your type of image.

With the ASI183M I simplified it to gain 53 for LRGB imaging and 300 second exposures at -10C (the camera would do -25C but unlikely to do that in summer).

I used gain 111 for narrowband and 600 second exposures. I did not touch the offset.

Whatever that translates to in QHY settings I don't know yet but I am like you new to QHY and I have 2 QHY cameras shipping to me so I need to study up on it myself. I can share what I find with you.

I think basically I will be using it similarly with 2 main settings. The LRGB setting and the narrowband imaging setting.

Think of gain as ISO on your camera (these are camera sensors being used). Too high a gain will reduce your dynamic range and reduce read noise but it also reduces the full well depth which is how many electrons can a single pixel hold before its full. Too low a full well depth will mean in astrophotography that your stars will overexpose too quickly, will become bloated and lose colour data. I see this often in CMOS images that start to look like many DSLR images where all the stars are white and featureless and a bit bloated.

This is one area CCD seems to hold an advantage. Star colours are more easily protected and CCD images tend to have more colourful stars. Flick through Astrobin images and you'll start to be able to pick which are CMOS and which are CCD just on that alone, its that common.

So I would pick the mode that suits best. With the QHY600m the characteristics of each read mode are listed. As I recall there is one where the read noise is low, the dynamic range is high, the full well depth is good. That would be the one to pick for general colour imaging for day to day imaging. For narrowband you would go higher gain as the signal is lower in narrowband so you are less likely to blow out highlights.

Greg.
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Old 05-12-2020, 03:30 PM
TrevorW
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wealth of knowledge as usual Greg, what QHY cameras have you gone for thanks
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Old 05-12-2020, 05:38 PM
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Thanks Trevor.

A QHY294M and a QHY600M Photographic model. Also got a ZWO ASI290m for an autoguider. It seems very clean compared to CCD and also no interference patterns I tend to get with CCD autoguiders.

Another thing is to inspect those performance graphs on the QHY website. They show the different performances in the different read modes. Mode 0 seems best for the QHY600M. It may be different for the 182C.

Greg.
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Old 07-12-2020, 08:32 PM
TrevorW
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I was thinking about this camera next



QHY268PH-C (PhotoGrapic Version) zero amp glow



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Old 07-12-2020, 09:18 PM
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IIRC, it’s the same sensor as the ZWO ASI2600MC, which looks pretty promising IMO.
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