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CMOS Dark Frames


centroid
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I have been building a Darks library for my 294c Pro TEC.
 
Given the 12 years of imaging I spent with CCD Cameras, CMOS 'Starburst' is something new to me, but expected.
 
Attached is a 240s Dark, taken at -10 degrees.
 
Apart from the 'Starburst', am I also seeing 'Amp Glow; at the top and bottom of the image?.
 
The image is cropped for posting, and ' stretched' for visibility.

240s Dark.jpg

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That is quite normal for that sensor and it calibrates out.

Even glow and star burst ADU values are not that big to introduce large noise in those places (maybe 2-3e of signal in there).

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I expected to see 'starburst' Vlaiv, as its inherent with the sensor, but not the 'glow' top and bottom.

On another forum, dedicated to the brand of camera that I am using (I will not mention the brand, as the Admin there are very sensitive to any comments that might be seen a negative to their products, even if factual), one member commented that he had the opportunity to compare this camera with a 294c based camera of another brand.

He found the 'starburst' was exactly the same, but the top and bottom glow was not present.

I wonder if anyone here, would like to confirm that they either get this top and bottom glow with the CMOS camera, or not.

Edited by centroid
typo
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If it helps, here is 4 minute -20C dark from my ASI1600:

image.png.40855386d28a74487079727b3fcbad02.png

It also displays such features and no real starburst.

On the other hand I have "triple" star burst pattern on my ASI178mcc

image.png.fa73448c5784d7cb9e6031814f03b6e4.png

Both cameras calibrate fine.

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6 minutes ago, vlaiv said:

If it helps, here is 4 minute -20C dark from my ASI1600:

image.png.40855386d28a74487079727b3fcbad02.png

It also displays such features and no real starburst.

On the other hand I have "triple" star burst pattern on my ASI178mcc

image.png.fa73448c5784d7cb9e6031814f03b6e4.png

Both cameras calibrate fine.

It calibrates fine, but I have often noticed a zone of lowered signal to noise in the area under the most intense part of the burst in the images of others. 

Adam

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You can see my Master Dark from the ASI294MC Pro in THIS THREAD. Converting to PNG from FIT has made it look cleaner than it actually is, but it shows what you're looking for.

The Master Dark is 20 x 300s at 120 gain and cooled to -10°C. ;) 

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14 minutes ago, Adam J said:

It calibrates fine, but I have often noticed a zone of lowered signal to noise in the area under the most intense part of the burst in the images of others. 

Adam

I've found that it is not that significant.

image.png.87aedd1a65e17978cb7ac76a17532183.png

Here is one dark calibrated with master dark. Yes, one can see visually that there is a bit more noise in corners (this is ASI178 data - one that has 3 strong star bursts).

and actual measurements of stddev in center and bottom right corner give:

image.png.a4d0857f1514040661d31f8a9d409e87.png

8.9 ADU vs 15.4 ADU

Not sure what the gain was for this particular recording (I just pulled dark from archive), but this camera has all the gain settings less than 1e/ADU, so actual noise levels in electrons are something like half that - ~4 and ~7. Total of 3e difference

I reprocessed the data from this session just a day or two ago (it's snowing so there is not much to do in terms of astronomy) and here is result:

m81-82.thumb.png.6f7a9080cb7d4e886e60a7462f16340c.png

This is two hours of 4 minute exposures (30 x 4 minute) in SQM18.5 with 80mm F/4.8 (F/6 with x0.79 FF/FR) and IDAS P2 LPS filter. ASI178mc-cool OSC camera.

Neither star burst nor additional noise can be seen in the corners.

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22 minutes ago, vlaiv said:

If it helps, here is 4 minute -20C dark from my ASI1600:

image.png.40855386d28a74487079727b3fcbad02.png

It also displays such features and no real starburst.

On the other hand I have "triple" star burst pattern on my ASI178mcc

image.png.fa73448c5784d7cb9e6031814f03b6e4.png

Both cameras calibrate fine.

It seems that they all have their individual quirks Vlaiv, being the "nature of the beast" I guess.

Cheaper than CCD of course, but there is no such thing as a "free lunch" 🙂

I note the dark frame from Budgie's ZWO 294 does not display the top and bottom amp glow that my brand of 294c camera does.

How nice the CCD days were, no starburst, minimal amp glow,  and no gain or black level settings to be concerned with. Unfortunately, less sensitive than today's CMOS sensors, and , more expensive.

I guess Starlight Xpress, ATIK, and others, will eventually have to move to CMOS.

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27 minutes ago, Budgie1 said:

You can see my Master Dark from the ASI294MC Pro in THIS THREAD. Converting to PNG from FIT has made it look cleaner than it actually is, but it shows what you're looking for.

The Master Dark is 20 x 300s at 120 gain and cooled to -10°C. ;) 

Indeed it does Martin. No top and bottom amp glow, which confirms what was reported on the other forum.

 

Same sensor, different hardware/electronics design.

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7 minutes ago, centroid said:

It seems that they all have their individual quirks Vlaiv, being the "nature of the beast" I guess.

Cheaper than CCD of course, but there is no such thing as a "free lunch" 🙂

I note the dark frame from Budgie's ZWO 294 does not display the top and bottom amp glow that my brand of 294c camera does.

How nice the CCD days were, no starburst, minimal amp glow,  and no gain or black level settings to be concerned with. Unfortunately, less sensitive than today's CMOS sensors, and , more expensive.

I guess Starlight Xpress, ATIK, and others, will eventually have to move to CMOS.

Have a look at ASI2600 mono model.

No amp glow, exceptional sensitivity - almost CCD like, but with all nice features of CMOS.

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A nice thought Vlaiv, but  we don't get enough of the clear, crisp winter nights that I enjoyed , back in my previous imaging days, (at least in my part of the UK), so LRGB imaging is no longer the option for me, that it once was.

I'm not qualified to say whether it is down to  global warming or not, but we seem to have milder winters that are plagued with cloud, so for me, OSC now makes sense.

I used LRGB imaging for quite a few years, with an SXVR H9 and then an SXVR H16.  Excellent cameras, UK made, and excellent customer support.

SX ccd cameras are still available, but as astro imaging is now a secondary interest to my photography, I must resist the temptation to buy one. 🙂

Edited by centroid
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8 minutes ago, ONIKKINEN said:

The rising cam version exists also. Much cheaper but does the same job, and has no "CMOS quirks" of ampglow, starburst etc.

So it can be done then 🙂. Seems that ZWO can eliminate the top and bottom 294 amp glow, but  Touptek can't, or don't bother.

However it seems that it can be calibrated out from the light frames, so a problem solved it would seem,  and  I guess I am going to find out.

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3 minutes ago, centroid said:

So it can be done then 🙂. Seems that ZWO can eliminate the top and bottom 294 amp glow, but  Touptek can't, or don't bother.

However it seems that it can be calibrated out from the light frames, so a problem solved it would seem,  and  I guess I am going to find out.

ahh, sorry meant the 2600 version exists as a rising cam version.

No idea about the 294.

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An interesting off-forums conversation with another user of the same brand of 294 that I have, reported  an issue of vibration from the fan, during long exposures, giving rise to rice shaped stars. Apparently, easily mistaken for coma.

He proved this by removing the DC power, and running on the USB alone, thus no fan, and the problem disappears. Reconnect the DC power, fan runs, and problem reappears. He says that he has seen other reports of this?

Hopefully, with the new WO flattener/0.8x reducer inline, which will bring my 115mm f/7 scope down from 805mm FL to 644mm, and f/5.6, I'll not be needing long exposures with the sensitivity of the 294 sensor.

This should also reduce the amp glow issue.

I have to say, moving from CCD cameras to CMOS,  has been a whole new experience. 😉

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