Double star imaging:Webcam Issues

[chiltonstar]

A question for the experts!

Trying my webcam (flashed Philips SPC880NC) on some doubles for the first time last night, I ran into a problem. In essence, because of the high gain necessary (everything turned up to max), the display and the stacked images (Registax) have very obvious banding. it is most obvious when imaging near the Pole as, even with my poor alignment skills, the image does not wander around in the field during capture (when this happens, the banding is "averaged out").

A bad example is this image, which is Polaris and its 9th mag companion.

Are there any solutions to this problem? Is it a problem with my individual webcam, or inherent?

Scope - 127mm Mak.

Chris

[Demonperformer]

Thinking on the hoof here, but how about moving the scope a little during the avi, so that you generate an artificial 'wander around in the field'?

[Merlin66]

have you considered using Florent Losse's REDUC program for double star measurements with a webcam??

The program is available free from Florent.

See:

HFOSAF

[chiltonstar]

Thanks for this - I'll start by exploring the movement approach. Easiest would be to gently rotate the Dec knob as the image is acquired so the image moves slowly across the field.

I must admit I was a bit surprised to see a star as faint as mag 9 in the first place with a humble webcam!

Ken - I looked at Florent's website - very interesting indeed!

Chris

[moflaher]

Or simply left the pair to drift, with drives off. That will create a trail, and measurements can be done afterwards

[nytecam]

Trying my webcam (flashed Philips SPC880NC) on some doubles for the first time last night, I ran into a problem. In essence, because of the high gain necessary (everything turned up to max), the display and the stacked images (Registax) have very obvious banding. it is most obvious when imaging near the Pole as, even with my poor alignment skills, the image does not wander around in the field during capture (when this happens, the banding is "averaged out"). A bad example is this image, which is Polaris and its 9th mag companion. Are there any solutions to this problem? Is it a problem with my individual webcam, or inherent? Scope - 127mm Mak. Chris

Hi Chris - nice start I've just downloaded SharpCap s/ware and find much more control of brightness etc to over-ride, to some degree, the Asdacam's auto-gain and testing many settings. Not sure if it works with your cam.

[JamesF]

I've experienced the same issue with my SPCs when I have the gain pushed up too high, so I think it's a generic problem.

James

[lunator]

Chris

I have not used a webcam for imaging doubles but when I did single shot afocal imaging the exposure times were between 0.5 nd2 seconds on the brighter doubles (mag 8)

Could slowing the frame rate down make it easier to capture the image?

Cheers

Ian

[chiltonstar]

Chris

I have not used a webcam for imaging doubles but when I did single shot afocal imaging the exposure times were between 0.5 nd2 seconds on the brighter doubles (mag 8)

Could slowing the frame rate down make it easier to capture the image?

Cheers

Ian

I'm using the slowest frame rate, and it works ok with "normal", bright-ish doubles, with not too dissimilar mags. With Polaris, I can get a decent image of the brighter star with low gain settings, but to record the faint companion, I have to turn the gain to max which produces banding and of course a bloated star image for the brighter of the pair. Maybe the answer is two images, and combine them in PShop.

Chris

[lunator]

Hi Chris, that might be the answer

I think that the frame rate issue will always be the limitation for webcam and fainter doubles,

You might have more luck with a low cost digital camera.

I got my best results with an old 3MP camera with a shutter speed of 2 seconds

Cheers

Ian

[nytecam]

Just a thought - webcams could perhaps do with a little light fogging during the exposure to reduce the on-chip autogain feature and resultant soot-'n-whitewash on single/double star images