weird artifacts

[Rus Belikov]

When imaging through my telescope at a very slow f/ratio (f/30), I get weird artifacts that look like fuzzy black dots. Please see the attached image. There are a couple very strong ones (e.g. one at bottom center), and a dozen small ones.

When I rotate the camera, the artifacts stay on the same pixels while the image rotates. Therefore, the artifacts are due to something on the camera.

When I use a fast beam, these artifacts go away. Therefore, they are not due to bad pixels and are probably due to dust on the camera window.

They have been present since the first time I tried the camera, and they don't change, so they are probably not due to anything I did, and probably not something that can just be blown off.

Could these be dust particles on the inside of the camera window? Is this normal or did I get a camera with ah unusually high amount of dust?

[bdeclerc]

Yes, this is dust, almost certainly on the little protective glass in front of the CCD-chip. At faster F-ratio's this dust is out of focus and a lot less visible, as you increase F-ratio, it becomes sharper and more visible.

You could try brushing it off with a soft camera brush, some of those also have a "blowing" mechanism to blow air over it to dislodge the particles. Keep the camera upside down when doing so, so the dust falls away.

Don't use "compressed air-in-a-can" for this, as that sometimes contains little oil particles which might stick to the glass and are harder to remove.

[dwsubc]

I got this as well because I was switching the camera between lenses a lot. I cleaned it off using a SensorBrush from http://www.visibledust.com and then sealed the camera with a IR filter. No problems since - touch wood.

Dave