Cam and focal length help

[gazza63]

Hello astronamers

I have modified my webcam to directly fit into my focuser tube. I would like to know if there was a program that could take the image further back, to get the whole view (full moon for instance). Is my view by using the cam directly, governed by the focal length of the scope? Scope being a 150/1200 f8, is great for objects far away.....but for the moon i cant get the full image in view. Any advice would be appreciated.

Thanks

Gary

[GaryG]

Hi Gary,

To get a wider field image you would have to use a reducer to effectively shorten the focal length of the scope. Alternatively you could take overlapping frames then use something like Microsoft ICE (free) or other panorama generator to combine the frames - this would give you the added advantage of higher resolution for your finished image

Gary

[Steve Ward]

A webcam view is roughly equivalent to that of a 6mm EP , you'll never get the whole disc in frame .

As GaryG suggests , take a series of overlapping AVI's , process them identically in Registax and stitch them together in MS ICE , just click on 'file' top left , click 'new panorama' , load the stills and it does the rest.

[JamesF]

The image scale is fixed by the focal length and the focal length of the telescope (without adding more optical components) is fixed, so the size that the Moon appears at the image plane is fixed. Roughly, you get about 3 arcminutes of sky per mm at the image plane with a 1200mm focal length which means the Moon is about 10mm across. As you don't say which camera you're using I'd guess that it has a sensor that's only 4mm by 3mm so you'd probably need sixteen panels (allowing for some overlap) to image the entire thing.

A focal reducer would reduce the effective focal length of the scope thus reducing the size of the image, but to be honest it's always going to be tight with a sensor that size as you need such a large reduction factor and they're not without their own problems, particularly regarding spacing between the camera and reducer.

The alternative is to use a different camera. A 10mm image would easily fit on an APS-C DSLR sensor in one hit, for instance.

James

[JamesF]

I realise I glossed over a load of maths in that previous posting. Do say if you'd like me to expand on it a little.

James

[gazza63]

Thank you all for the advice. I'll give it a go tonight (weather permitting) of stitching, and see how it comes out. i will re-post the images on here if successful?

fingers crossed for clear skies eh!

[Steve Ward]

Here's hoping . . .