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Newb trying astrophotography - some Q's

Started by joburg-astro, 01/18/2005 02:02AM
Posted 01/18/2005 02:02AM Opening Post
Hi all

I have a 60mm department store refractor and a 750mm f/5 newt reflector.

I have modified a no-name brand webcam.

I have been taking some pics of the moon with the refractor but when trying this with the reflector I have been unable to get focus - how to explain - I start getting focus turning the focuser wheels away from me - ie. the camera is going towards the scope - and then I run out of focuser tube smile Hope that makes sense. What can I do to get around this problem.

Do I need a focal reducer or will buying a Logitech Quickcam Pro solve this problem?

Thanks in advace - oh yes I have atached a photo taken with my refractor - lemme know what you think.

regards
Douw
Johanesburg SA

Attached Image:

joburg-astro's attachment for post 21595
Posted 01/18/2005 05:29AM #1
This is a rather common problem. It's called lack of backfocus.

If you are using a diagonal, remove it and try again.

Getting a new webcam may solve your problem, but may not. It is simply a question of where the chip is compared to where the optics of the eyepiece would be. THe refractor focuses an image at a certain point. The job of the focuser is to hold the optics of an eyepiece (or in your case webcam)at that point. A focuser is movable because different eyepieces are built to different specifications. (And because if you were using the telescope at less than infinity, it would need to move the eyepiece further out, and because the length of the tube changes when it gets cold or hot, and for a number of other reasons.)

In some eyepieces the actual optics are further up the tube of the eyepiece than in others. The focuser compensates for this.

Your webcam's "optics" just happen to be further back than your typical eyepeice. So, even when your focuser tube is "shortened" as far as it can go, the chip is not where it belongs.

Alex
Posted 01/25/2005 11:38AM #2
I think the image is shockingly good considering the equipment. I never knew that the moon had an atmosphere, though.