View Full Version : Artefacts normal/abnormal?

February 28, 2008, 08:33:13

I bought and testet a FireWire DMK 21AF04.AS Kamera at my scope. After adding several images I have seen some artefacts and don't know if they are normal/abnormal without darks.
First pic(M51) is made of 34 pics a 16sec. exposure time without darks/flats. In the left upper corner there's like a amplifier glow and left stripes down.

Second pic(M42core) is made of about 300pics with much shorter exposure time, I don't know but think 1 second. The same left side horizontal more black lines after adding. One picture from the video shows only repeating noise structures in the left half side but not random like in the right side.

All are made on a mount so they move only small way during exposing. Is it a known appearance?

CS, Lars

February 29, 2008, 00:28:34
Hi Lars,

I have no answer for the vertical lines in the first image. have never seen them on my cameras.

Yes the artifacts in the seconds image are normal. You surely had gain up to 1023, correct ?

When you make long time esposure you do not need to push up the gain so much. Up to 500 - 600 you have no noise still.

February 29, 2008, 14:35:25
Hello Rainer,

thank you for your answer, that's more than my selling company could say. I'm shure that I used the maximum gain. So fixing the problem should be easy. Fortunately now it's weekend and I will do some tests indoor or outdoor, we will see.
The other noise pattern should be no problem with a dark because it's static in every picture. But why it is on the left side? What's there electronically?
And I will have a look at the cable length because with my 5mtr. extension cable at the origin cable this camera will not work :mad:

CS, Lars

Stefan Geissler
March 3, 2008, 10:27:54
Hi Lars and Rainer,

sorry for the long delay of my answer.
Regarding the first images: Yes, as Rainer wrote, the brighter lines are normal. They are caused, as far as I understand, by different heating up of areas of the CCD.

Regarding the second images:
Rainer's answer and solution is correct too. The lines are created by the noise of gain and are amplified by the statistical distribution on the CCD. (That is what I understood after speaking with the engineers.) At least, gain produces noise in any way, thus it should be used carefully.