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rule of thumb - with a quality webcam, multiply the pixel size in micron of your camera by 4x and then get a Barlow that takes your scope up to about that as an f number (or maybe a little more if your camera is very sensitive). This rule automatically takes care of limiting resolution and scale issues.
I think an SP900 has 5.6 micron pixels, so you should aim for about f22. A 4x Barlow would do the job, bringing your f6 up to f24. Recommend a 3x TV Barlow with an extender to get it up to 4x (the TeleVue site tells you how much extension you will need).
if you later get one of the new high performance cameras with 3.5 micron or smaller pixels, the 3x without extender should be about right
Edit- Peter posted before mine was completed - we agree.
Last edited by Shiraz; 22-02-2013 at 11:18 PM.
Reason: modify rule of thumb for lower sensitivity cams
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