Shhh! I'm huntin wabbits

[JamesF]

Well, bunnies, actually, of the dust variety.

When I was imaging Jupiter at the weekend it became obvious that the little devils had been multiplying like, well, rabbits, all over the sensor of my SPC camera. How they managed to do so given that the camera has had an IR filter and cap on all the time I really don't know, but there it is. Unfortunately the size of the sensor and target tends to mean they don't get lost in the noise and stacked out in processing, but can end up being made even more noticeable after stacking, so I want to get rid of them.

To my eyes, even with a magnifying glass, the sensor appears clean, but when I was imaging it clearly wasn't. Then again, a piece of dust doesn't exactly have to be very big to occupy quite a noticeable chunk of the image area when the sensor is as small as that of an SPC.

Does anyone have any handy hints for checking the cleanliness of the sensor without actually having to put the camera in a scope so, for example, I can plug the camera into a PC on my desk and work on it checking progress as I go? If I took a frame or two of an evenly lit sheet of paper and gave the histogram a fairly serious stretch would that be likely to do the job? Or am I barking up the wrong tree entirely?

James

[NickK]

It should work - the main thing is to ensure the sensor is not being saturated. Lastly if the sensor is cooled then you may find the cleaning solution freeing.

[JamesF]

I'd not thought of things freezing on the sensor. Shouldn't be an issue with this camera though -- it's a fairly standard SPC880 with the firmware upgraded. I have an LX-modded one with a fan but I can't imagine that would get close to freezing unless it was pretty chilly outside.

I'll give it a go and see how I get on.

James

[Digz]

Just to confirm they are on the sensor try several shot rotating the camera after each shot if the bunnies move the are on the sensor, if the don't, they are elsewhere. Have you tried a rocket blower?

Your suggestion of shooting a sheet of paper might work. It's similar to what I do with my camera to check the sensor is clean.

[JamesF]

They move with the camera even when I remove the IR filter and they're in sharp focus so I'm fairly sure they're on the sensor. I have a rocket blower, but I don't think I've had a webcam sensor yet that didn't have some dirt on the sensor that just didn't want to budge

James

[Digz]

Yeah I know the feeling. I have a pack of sensor swabs and a clever gas powered contraption that creates a vacuum to suck dirt off. Come to think of it I wonder if you cut a slot in a straw to make your own vacuum contraption would work?

[JamesF]

Now there's a scene with Wile E. Coyote just waiting to happen

James

[Digz]

Now there's a scene with Wile E. Coyote just waiting to happen

James

[DBushell]

Perhaps the dust is on the IR filter rather than the sensor?!

[jgs001]

I found that I had to connect the webcam to a slow focal ratio to exacerbate the dust and make it obvious... then point it at a blank wall. Doesn't matter it that's a fast (ish) refractor barlowed, or a Mak, what ever is easiest to mount and easily manouvered (I used to put a skymax 102 on a camera tripod). I found a rocket blower did very little, and ended up using a wet clean. I also found it extremely hard to get the sensor even vaguely clean (that was with holding/mounting it so the sensor was angled downwards.)

[Zakalwe]

Just take flats. If you use Autostakkert then the process of calibrating is dead easy

http://www.schursastrophotography.com/solar/Articles/solararticle5.html

^^This is for Solar imaging, but the technique is similar for planetary (you will need a light source). Mind you, I tend to find a clean area of the chip for planetary.

If you are doing Lunar, then the Solar method above will work a treat by just defocusing on the Moon.

Using Barlows makes the bunnies much more noticeable too.