The magnification of the imager Toucam is such that it only photographs a segment of the moon. Wanting to photograph the whole moon and having read where one can reduce the magnification using a focal reducer, I contacted a Sydney firm requesting information while providing the telescope specifications and was told I could purchase a reducer that would provide .7 and .5 reduction, which would allow the whole moon to be photographed.
I received a single lens, marked 1.25 Focal Reducer, similar to a 1.25 filter, with a note to say the remaining section (what ever?) to follow when stocks arrive.
Screwed to the Toucam I found I could not focus the imager. The moon could be vaguely seen on the computer screen, but I couldn’t rack the device, further IN, it being at the limit of the focuser.
I made a temporary plastic 1.25 mm adaptor, which provided a further reduction of about 10 mm, but to no avail. I made an adjustable tube; about 50 mm long, which received the reducer lens and the tube screwed to the imager. Not knowing how long this should be it failed to come to focus. Is there some kind person who could advise me what I need to do to bring this device in focus, or am I expecting the impossible?
Telescope specification
Dob, 205mm , F5 mirror. The information below, so kindly supplied, convinced me to purchase the reducer:
Quote: The Reducer will reduce your focal length by either .7 or .5 That means that your focal length will go from (8" f/5) 1016mm to 711mm (.7) or 508mm (.5) resulting in wide field of vie and therefore you would be able to fit the whole disk of the moon in.
Great if I could focus the device! Or is the secret in the remaining section not supplied? I’m new at the game, old, but not too old to accept advice!
Hmm, I'm surprised no one else has jumped in on this yet, perhaps they're all away for Easter.
I am curious about the fact that you were sold a focal reducer for a newtonian. In my previous experience focal reducers were only for Schmidt-Cassegrains (SCTs). SCTs have HEAPS of focuser travel and this issue you're experiencing wouldn't occur. So if someone has anything to say about this I'd be interested too.
Otherwise I have a couple of suggestions:
1. If you can't acheive enough intravel with the focuser in the dob you will ned to move your primary mirror up the tube when you plan to do imaging. When you want to do some visual viewing you will need to move it back down again. A bit of a hassle, and you would need to collimate every time you shift (so if you're not confidant with that I'd get practising). I would not be able to tell you how far you need to shift, though, in this situation.
2. Buy another scope that has a short focal ratio already and use that for widefield imaging. Don't laugh or scoff, thats what a lot of serious astrophotographers do - get the right tool for the job.
3. Forget about the focal reducer and invest in some good software that will stitch your smaller images into a larger mosaic. Perhaps a visit to the software forum here will help you out.
Thank you Blueskys. As an old experienced tradesman I appreciate an honist reply as you made. AS I wrote, I have no faith that the reducer will work as stated when the extension tube arrives.
My scope is a trust mounted dobsonian, self made and it would not be possible to move the primary mirror. I could make adjustable trusses but first I'd have to experiment to find just how much movement is required.
I would like to add here that the scope's speci was provided before purchasing.
Again I thank you for your reply.
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