Help with this shot...

[2020BC (Bill Christie)]

Can anyone help me with identifying the cause of the "brush marks" on this image.

Between the red lines and in the same direction as the red lines you'll see what could be described as brush strokes as though this was a painting or a charcoal drawing. What are these, why are the spoiling this shot, and how can I be rid of them?

[Alchemy (Clive)]

Just a guess, but it appears to be most evident in the brightest parts of the image, check the 2 small craters with lines under them going down. i suspect your tracking was out during the exposure and stacking has left little tell tale marks behind.

i cant explain off the top of my head how this happens but i have seen it on my images and that was the cause in my case.

[iceman (Mike)]

Were these with the video camera, Bill?

What do the raw frames look like?

[2020BC (Bill Christie)]

These were taken with the Mintron 13V1C video camera. This is a raw frame.

[iceman (Mike)]

It looks like it's a result of the stacking then?
How big was your alignment box? What was your tracking like during the avi?

[2020BC (Bill Christie)]

Originally Posted by iceman

It looks like it's a result of the stacking then?
How big was your alignment box? What was your tracking like during the avi?

Alignment box was 256, but I also tried it at 128.

Hand-guided during recording.

Registax was able to track the selected alignment point without any errors.

[joshman (Josh)]

i odn't know what i'm on about, but can you select several alignment points during stacking?

[bird (Anthony Wesley)]

Bill, does the camera have any hot pixels? These could cause this sort of mark during stacking.

cheers, Bird

[2020BC (Bill Christie)]

Originally Posted by bird

Bill, does the camera have any hot pixels? These could cause this sort of mark during stacking.

cheers, Bird

Yes, it does have some hot pixels, however these don't normally show up in my other images. I have a more usual problem which is due to dust specs on the CCD, however even these don't account for the lines in this instance. I'm thinking it's processing artifacts maybe in combination with dust motes - maybe....

[bird (Anthony Wesley)]

spots (or hot pixels) will turn into streaks during processing if the image moves around, in this case maybe the image moved while you were capturing, and that turned hot pixels or dust motes into stripes?

cheers, Bird

[2020BC (Bill Christie)]

Originally Posted by bird

spots (or hot pixels) will turn into streaks during processing if the image moves around, in this case maybe the image moved while you were capturing, and that turned hot pixels or dust motes into stripes?

cheers, Bird

With my mount the image bounces around the screen quite a lot (periodic error, wind, etc.). At 6.4metres focal length it requires frequent guiding to keep the image centred. Maybe next time I'll concentrate more on reducing the movement. Thanks!

[Dennis]

Hi Bill

I’ve encountered a similar phenomenon with my cooled SBIG ST7E when taking short duration exposures (less than 30 secs) and noise begins to dominate the frame. When I stack such frames, it looks just like your example.

On longer exposures, (over 60 secs) where signal dominates, these artefacts are not there.

Cheers

Dennis