How powerful a Powerate is too powerful

[Uplooker]

I wish to purchase a TV Powermate, primarily for planetary imaging with SPC 900 webcam. I will use it with SW 150P 6 inch F5 newtonian.

How powerful is too powerful for this scope - x3, x4 or x5. How do i calculate the correct power for a given scope?

I am also mindful that over a certain power the image will be too large for the CCD of the webcam. Again, how do i calculate the correct power.

Any advice appreciated.

Ian

[Merlin66]

Think in terms of the final f ratio. Your telescope is f5 so with a x4 powermate you'd get f20, likewise an x5 would give f25.

Planetary imaging is usually around f20 to f40+ depending in the seeing conditions etc.

Remember the x2.5 and x5 powermates are 1.25" fitting and the x2 and x4 are 2" fittings.

Use CCDcalc to work out the size of the image on your camera. The focal length is used to calculate the plate scale.

The New CCD Astronomy Home Page

[brianb]

Learn to use a relatively small f-ratio first - it's easier - f/15 to f/20 should work reasonably well if you get your scope well collimated. f/30 demands steady seeing and the sort of technique that takes a couple of years to develop.