Cleaning ED80????

[Lee]

My ED80 is fully equipped with a very dusty inner objective lens surface.... see my horsehead pic from today for example.....
How could I clean it? - does the objective assembly unscrew off? - I haven't tried to in case I bugger something..... if it does unscrew, should I? Is there any critical reason why I shouldn't.
I realise I need to use flat frames, but at least reducing the dust now and again can't be a bad thing????

[allan gould]

After looking at your horsehead shot, the dust is on your DSI and not in your ED80. Anything on your main optics would be so far out of focus that it would degrade your image and not be seen in your photo as "spots". Also you should be able to go longer with the Losmandy mount with PEC and the ED80 in the train as it is not a very demanding combination/focal length. Also is your computer using USB 1 or 2? I might make a guess and say USB1.1? You need USB 2 to run a DSI as it gives horizontal banding with USB1.1.

[Lee]

OK.... the DSI looks spotless, although it is hard to see..... Only my second real session with the DSI, so will get to longer exps soon, probably should have shot something else at 1 minute though. Still working out the idiosyncracies of the unit and software (many!)

The computer is USB2 I believe (its my partners windoze box) - I can't find anywhere that it is USB2 or high-speed USB, but it copies a 190MB folder of files in 35 sec, as does my USB2 Mac - so I assume it is USB2. The lines apparently can also be caused by too much temp separation between darks and the lights, and something to do with "line delay"....

[Garyh]

Hi Lee, wouldn`t hurt to give it a clean..you will have to collimate it afterwards, which would be easy with a laser.
I had dust spots similar early this year with my canon 300d and it turned out to be dust on the sensor uv/ir filter, very hard to see but it was there. A soft camel hair brush and some blowing fixed it fine..
Try shooting during the day at something like some clear sky then rotate your DSI and see if the spots rotate with it or stay the same. May help to find that dust.
Usually dust on the main objective will just scatter light and give you a lower contrast image like Allan says that being so far from the focal plain should not show as spots....the closer the dust and dirt to the ccd the more pronounced the spots..the higher the F/ratio the sharper/easier the dust spots are seen too..
Cheers Gary

[Dennis]

Hi Lee

Even if you inspect the DSI chip window with a magnifying glass you are unlikely to see the dust bunnies - they really are small. Be careful as "incorrect" cleaning will introduce even more dust bunnies.

See here for cleaning ccd's (http://www.cleaningdigitalcameras.com/index.html)- following these guidelines has helped me keep my ccd's cleaner, with confidence.

Cheers

Dennis