Short exposure issue with SBIG STL 11k


#1

Hi All,

using my SBIG STL 11000 to take short exposure I got this strange issue:

for exposure below 0.1sec the image seems corrupted and split in two parts
(Please see screenshot here)

No problem with exposure longer than 0.2 sec.

Moreover using very short exposure the image seem not related to exposure time (i.e using 10 or 20 millisends I got exactly the same image with the same ADU levels.)

These short exposures are very useful in my case to take flat shots with fast telescope and different filters (L and H alpha) without any change on the flat panel.

It seems a bug but please let me your comment.

Logfile here.

Thanks in advance.
BR/Gianni


#2

Gianni,

I don’t think this is a bug in SGPro (or if it is, I have no ability to fix it). It works with the SBIG provided sim without error so I’m not sure why you are seeing it. You may want to confer with SBIG. Also, @Jared has / had one of these cameras and used to see horizontal banding sometimes. I think it was related to something with the TEC, but he might be able to provide more detail.


#3

The stl11000 is certainly not made for short exposures. Guite opposite really. The shutter likely can’t move fast enough to even take exposures below about a second.

As for the banding I would see that when the camera was over -20C. So I always make sure to keep it cooled at or below -20C. Makes it hard in the summer! But this was at all exposure lengths.

I don’t think you’re going to have much success with that camera and sub second exposures. I don’t think the hardware is up to that task.

Jared


#4

I’ve been using an STL-11002 and SGP for 2-1/2 years. My BIAS frames seem fine, They are taken at a nominal 000sec in SGP and, in the dark.

For flats, one always wants to aim for a minimum of a few secs to allow the mechanical shutter to get out of the way. Shorter than that risks differential shading across the frame caused by the shutter.

As I understand it, and certainly as I experience it, the KAI-11002 chip is subject to vertical, not horizontal banding. It seems we are discussing something different? I’ve never seen even a hint of horizontal banding. However, I see vertical banding routinely and must process to suppress it. I use Bob Franke’s CCDBandAid to do that. This is freeware, generously made available by Mr. Franke on his site.
Link: CCDBandAid


#5

Hi all, thanks for your inputs.

Sbig 11k is an interline ccd and from my experience, is capable to take short exposure using elettronic shutter, without any issue in terms of shadow from mechanical shutter. In the past I used very short exposure with other SW without problems. Also in specs Sbig declare 1msec as minimun exposure time.

My issue is not related to STL11K vertical banding, is a sort of horizontal image split. Let me to explain better with an example:

Today I tried this simple exercise with SGP and camera in the dark and capped:
taken one shot with “type” = flat and exposure = 0; then a second shot with “type” = bias and again exp=0;

The two shots should be the same but they are different.

The “bias” frame is the typical bias frame from STL11002, dark in the upper part and then progressively lighter in the bottom.
The “flat” one is different and shows a sort of band in the upper part of the frame. The upper part is lighter, then darker and then again progressively lighter. The top light band is about 1/4 of the frame or about 680 pixel.

You can download the two shots here (bin 3x3, but the issue is present in bin 1x1 as well):
bias
flat

Any thoughts?
BR/Gianni.


#6

Just to complement my previous comment:
The two shots (bias and flat) are exactly the same if the exposure is longer than 0.2 sec, and I’m talking about shots taken with capped camera.
BR/Gianni


#7

SGP doesn’t do anything different for short or long exposures with the SBIG. We simply tell it how long to expose for and read the data off the chip. I’m not sure if we should be doing something different for very short exposures or not. I’ll thumb through their documentation and see if anything sticks out.

Also the issue that I spoke of was horizontal banding but it was present in all exposure durations when the camera wasn’t cooled below -20C. It generally showed up as 4 bands if I recall correctly.

Jared


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