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Old 27-05-2015, 08:37 PM
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PRejto (Peter)
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White left edge of Trius Images?

Hello,

I'm using TSX CAO and my Trius. My lights and darks all show a rather strong white border on the left side. Do any of you with the Trius see anything similar? I get this border both using ASCOM or the SX H694 driver in TSX.

The attachment is a dark master made in CCDStack.

Thanks,

Peter
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Last edited by PRejto; 28-05-2015 at 04:56 AM.
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Old 27-05-2015, 09:18 PM
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Yes I do. It seems to subtract out and I don't notice any problem with the calibrated images.

Greg.
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Old 27-05-2015, 10:11 PM
SpaceNoob (Chris)
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Looks pretty clean to me, how high is the ADU for that region over the background average? I'm guessing pretty low noise if its a 694 sensor. I pretty much see one on either side of my bias frames with an 8300. Master bias = gone.

Perhaps subtract a master bias from your dark to see if its gone and simply a result of readnoise? If not, try a 5min dark and see its value, could be noise building from the amplifier over time?
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Old 28-05-2015, 05:22 AM
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I have also noticed some minor amp glow in your frame - nothing to worry about, I think it is common for cameras with Sony's sensors.
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Old 28-05-2015, 01:13 PM
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Thanks for all the responses. I feel better (I think!).

Yes, if I subtract the master bias from the master dark I cannot see the line.

As best I can tell the difference in ADU between the brighter edge and rest of the frame ~120 adu (1330-1280).

If I completely calibrate the subs, after stacking I can still detect a bit of brightness on the left edge. Normally this might not matter so much but I'm combining Trius RGB with luminance from a chip with a slightly larger FOV (KAF8300) on my TEC180. Doing so does make it stand out so I'm forced to crop down a bit. Not a big deal but recently it's been bothering me.

Slawomir, how do you see amp glow in the frame. I'm not sure what to look for? I see a pretty even spread of 1280-1281 over the whole frame (excluding the edge).

I've been in the habit of not using darks/flats due to reading that it often introduces more noise than it cures. However, then I'm left with the white edge that I must crop out. Is it recommended to just do a bias subtraction? How many bias frames should I take to not introduce noise by doing this?

Thanks,

Peter
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Old 28-05-2015, 04:21 PM
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Not sure about that technically. Why would you subtract a master bias from a master dark? The master dark already has the master bias component in it and you would want that when you subtract it from your light as the light would have the white edge in it.

As I understand it bias are more for flats unless you want to scale your darks which is handy at times.

Greg.
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Old 28-05-2015, 05:46 PM
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Quote:
Originally Posted by gregbradley View Post
Not sure about that technically. Why would you subtract a master bias from a master dark? The master dark already has the master bias component in it and you would want that when you subtract it from your light as the light would have the white edge in it.

As I understand it bias are more for flats unless you want to scale your darks which is handy at times.

Greg.
Hi Greg,

I don't normally subtract a bias from a master dark! Spacenoob said I should try that as a test which I did and got the predicted result.

I did experiment by subtracting a bias frame from my lights and that seemed to do as good a job removing the white line as a master dark. I just wonder about the advantage or disadvantage of doing that given previous statements by others on this forum that dark calibration can add more noise than it removes. Also, Terry Platt responded to me and said:

"Itís a very slight overshoot in the CCD amplifier, caused by the sudden DC change at the start of each line. Itís a Ďbiasí artefact and is completely removed by a bias subtraction."

Peter
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Old 28-05-2015, 06:45 PM
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Hi Peter,

Please check the attachment - I have further stretched your frame to highlight the amp glow. Again, I have seen this in other cameras with Sony's sensors so do not worry. It might be because of their higher sensitivity so that the CCD is picking up faint signal from within the camera. It gets bigger with longer exposures, but still is not noticeable at all in the light frames.

As for dark calibration, it will add more noise but hopefully at the same time remove more significant camera-induced artefacts. I only use bias subtraction (ICX814) and make a master bias from 250 frames.
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Old 28-05-2015, 09:06 PM
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I just got my Trius SX674 today. Ran some tests and can confirm a similar bar on mine, although it's inset from the left edge a little bit. No discernible amp glow on mine, but I wonder if you had cooling enabled when you ran that (I did)
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Old 28-05-2015, 09:38 PM
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Quote:
Originally Posted by gregbradley View Post
Not sure about that technically. Why would you subtract a master bias from a master dark? The master dark already has the master bias component in it and you would want that when you subtract it from your light as the light would have the white edge in it.

As I understand it bias are more for flats unless you want to scale your darks which is handy at times.

Greg.
Just an experiment to isolate the cause Greg, nothing about image calibration.

If it disappears after bias subtraction, it's read noise associated. Any remaining, would likely be as a result of a number of factors. amp, temp variance across the ccd etc and would build over time.

I don't use a Sony sensor, but even if I did, I would calibrate with bias, darks, and flats regardless.
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Old 29-05-2015, 05:16 AM
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I just got my Trius SX674 today. Ran some tests and can confirm a similar bar on mine, although it's inset from the left edge a little bit. No discernible amp glow on mine, but I wonder if you had cooling enabled when you ran that (I did)
Congratulations on your new camera!
As for the glow, try a 20 minute single dark frame and see if there are any signs of it. (Peter's dark frame was a 5-minute one and cooled to negative 10 C - I believe).
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Old 29-05-2015, 06:26 AM
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Congratulations on your new camera!
As for the glow, try a 20 minute single dark frame and see if there are any signs of it. (Peter's dark frame was a 5-minute one and cooled to negative 10 C - I believe).
lol, yep, that was pretty silly of me in retrospect. I'll try some longer exposures tonight.
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Old 29-05-2015, 06:51 AM
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I don't use a Sony sensor, but even if I did, I would calibrate with bias, darks, and flats regardless.[/QUOTE]

These sensors are so low noise that when you do a dark subtract you will visually see the increase in noise. It seems counterintuitive but that's what happens.

But a master bias subtract seems like a good thing.

I sometimes do full calibration and sometimes not. It depends more on whether I have dust donuts, vignetting or if I took a longer exposure.

Greg.
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Old 29-05-2015, 12:13 PM
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Quote:
Originally Posted by gregbradley View Post

These sensors are so low noise that when you do a dark subtract you will visually see the increase in noise. It seems counterintuitive but that's what happens.

But a master bias subtract seems like a good thing.
I totally agree. That's why now I use 250 frames to create a master bias frame that is very smooth.
Generating a master dark from so many frames is simply not practical, and using a master dark generated from a significantly lesser number of frames will add noise to the light frames, because these sensors are really low noise.
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Old 30-05-2015, 06:45 AM
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Slawomir,

Thanks for showing me ow you determined that I have a bit of amp glow.

I think I will also create a bias library of 250 frame!

Terry Platt said that if I continued to be bothered by the white edge they could make an adjustment inside the camera. I'm not sure it is worth the expense to ship it to England...

Peter
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Old 30-05-2015, 08:45 AM
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Yes I read a post by Terry and an owner where Terry adjusted the camera firmware for a particular issue one owner had and it resolved his difficulty.

Greg.
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Old 30-05-2015, 11:02 AM
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Congratulations on your new camera!
As for the glow, try a 20 minute single dark frame and see if there are any signs of it. (Peter's dark frame was a 5-minute one and cooled to negative 10 C - I believe).
Ok, I got a better dark, 20mins @ -10c (see attached for a very stretched version of it); still no signs of amp glow on this one. Looks like I got lucky... not that it'll make much difference.

Quick test suggests that going from -18c to 0c roughly doubled the noise in 30s darks, although I'm not sure it was significant anyway.
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Old 30-05-2015, 02:09 PM
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Hi Lee,

This frame does look very even and low noise.

Happy days! :-)

Now just need to get some clear skies...
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