CCD defects on chip

[peter brown]

Hi all,
I have purchased a Meade DSI III colour camera (second hand) and on connecting it to laptop with out telescope, there are multiple doughnut artifacts on screen which appear to be similar to those experienced on a phillips webcam that I have.
Is this a common problem? Will it effect any images as I can't see that the camera takes flats?
Many thanks for any help....Peter B

[rat156]

Hi Peter,

These are dust doughnuts. Caused by very small bits of dust on the surface of either one of your filters (if you're using one) or the glass at the front of the CCD.

They can be cleaned off relatively easily. One of the best ways to get rid of them is called an Arctic Butterfly, see if you can get one, they're worth every cent you spend on one.

Flats will help to remove them, electronically (and any vignetting in your system), but it's better to remove them, physically.

Cheers
Stuart

[theodog (Jeff)]

As below, but I use a can of comperssed air with a mini vaccuum cleaner (used for computers).
Gently blast every surface with the suction nearby. Don't let anything touch the optical surfaces.
What can't be removed by this can be removed using the Flat-field method during processing.
They are a common problem, like dog-hair on my eyepieces, don't get to stressed about them.

[bmitchell82 (Brendan)]

Normally your dust bunnies/doghnuts come from your optical system as dust that close to a CCD would compleately block light hitting that particular pixel. You can definately take flats with any CCD and it is advisable to do so for the best possible outcome, search the forum as there are many threads relating to this topic.

[Hagar (Doug)]

Dust can be removed easily by a dry bulb blower and any stubborn bits can be removed by gentle cleaning the CCD wit Isopropyl alcohol, then blowing clean with a dry bulb blower.
Flat frames will remove a lot of artifacts and any vignetting during software pre processing.
To take flats you need to have an even diffuse light source that will allow you to take evenly lit frames which can be applied to your light frames to reduce these problems.
Give me a call or drop in and I will show you how to do it the easy way.

[turbo_pascale (Rob)]

Originally Posted by theodog

As below, but I use a can of comperssed air with a mini vaccuum cleaner (used for computers).

Please avoid use of compressed air cans unless you know what you're doing.

Hold them wrong and you get a jet that will freeze things, not to mention the impurities in them which can sand-blast the area.

If you know what you're doing, feel free, but a giant hand-held blower is cheaper, and will last longer, and will do no damage to the equipment.

If you can, hold the CCD above your head (or at least vertical), so that when you dislodge it with the blower, use gravity to assist in it falling clear of any other internals.

Turbo

[theodog (Jeff)]

Originally Posted by turbo_pascale

Please avoid use of compressed air cans unless you know what you're doing.

Turbo

Couldn't agree more.
One would assume enough nouce to aviod direct blasting and any more than a "cross breeze". If you form frost on the surface, please don't operate on me. A little to heavy handed for mine.

After much stuffing around with some images, I do find dust-rings, but rarely. Often without flats, I target some of the fainter objects with good success.

However, be carefull with any optical surface and only approach when absolutely req'd.

[leon]

And again, stay well away from that compressed stuff, unless you are very experienced, one wrong move and the chip is frozen, I have Giotto Hand Blower, never use anything else, they do a great job.

Leon