racetrack? read noise?

I was hoping someone could tell me about the swooshes. These were short (3sec) exposures as I was playing around with image scaling. Obviously very stretched here. Camera temperature was -40C. (almost as cold as my feet felt). Looks like it must be something to do with read noise, (?) but I don't recall this discussed. Thoughts?

Thanks,
Charlie

Attached Image:

Is that a single frame?

Alex

Looks like some sort of CCD amplifier over-shoot
on the saturated stars. The amplifier over-shoots zero
and goes negative for a couple pixels, when the image is
readout. Readout is typically from left to right.
Its probably a design problem in the camera. I suppose
there is a some remote chance there is an adjustment
for it on the circuit board, but likely not.
Does not look very serious. I'd just ignore it.

Hi Charlie,

I wouldn't worry about it. Really short exposures like that are only good for planetary work. For which your camera is not ideal.. Send us an image with 3+ hours of exposure, processed with sigma reject. If these traces are still there then there is a problem. It looks like you have a prime imaging location. Could you tell us more about it???

Jeff

Hi Charles,

I have seen this on short exposures on a couple of occasions with my ST10 too.Can't tell you what is causing it though.

I try to go at least a couple minute with mine,it's happier then.


Jason

What you are calling "swooches" are actually "Ears", I believe.

Ears are taken to result from slow rebound of a digital to analog converter (DAC) when driven to saturation. They are common on the SAC-8 camera (long exposure modified webcam), but they are very short (leading to the VanGogh analogy as there is only one "ear" present for a bright star) while yours are much longer. There's a comment already posted along this line.

Several possible approaches:

You can ignore them and put a false floor in the image just above the true background level.

You can shoot shorter subs rather than longer, until the bright star no longer saturates. (so try a second or less exposures?)

Clone tool, etc, to patch background eliminates ears themselves crudely.

An aperture mask with a 60mm or whatever diameter hole placed over the open end of your telescope could be ideal for getting control of these over-bright stars that are saturating when exposure is set for faint nebulosity. That seems worth trying.

Hope this helps.

Tom Lindquist

Charles Hakes said:

I was hoping someone could tell me about the swooshes. These were short (3sec) exposures as I was playing around with image scaling. Obviously very stretched here. Camera temperature was -40C. (almost as cold as my feet felt). Looks like it must be something to do with read noise, (?) but I don't recall this discussed. Thoughts?

Thanks,
Charlie

Charles Hakes said:

I was hoping someone could tell me about the swooshes. These were short (3sec) exposures as I was playing around with image scaling. Obviously very stretched here. Camera temperature was -40C. (almost as cold as my feet felt). Looks like it must be something to do with read noise, (?) but I don't recall this discussed. Thoughts?

Thanks,
Charlie

Charles Hakes said:

I was hoping someone could tell me about the swooshes. These were short (3sec) exposures as I was playing around with image scaling. Obviously very stretched here. Camera temperature was -40C. (almost as cold as my feet felt). Looks like it must be something to do with read noise, (?) but I don't recall this discussed. Thoughts?

Thanks,
Charlie