Barlow for planetary imaging

[Camelopardalis]

Folks,

I'm looking to optimise my planetary imaging setup. I've read the threads about pixel size and focal ratio (thanks Ray!) so given that my cam has pixels of 3.75 microns, I should be looking to image at about f/19. My usual rig is either my C8 or C11 with a 2.5x Powermate.

Any suggestions for hitting that sweet spot...or should I not be too worried about the focal ratio difference?

Cheers,
Dunk

[Shiraz]

2x would be almost ideal, but 2.5 will probably still be quite usable with an efficient camera. Your signal level will be down by a factor of .67 over what it would be at 2x, so you will need to run at lower framerate than you could at 2x. If using 2.5x in less than optimum conditions, you might be able to get some benefit from high framerates with 2x2 binning.

In general, a normal Barlow is better than the 2.5x Powermate for this task, because you can change the fno by varying the Barlow/sensor spacing - the Powermate has extra lenses to keep the magnification constant.

[Camelopardalis]

Thanks Ray! My wish is to get the best signal that I can, and that I can afford.

I'm using a flip mirror so the Barlow-sensor spacing would be a problem, unless I put the flip mirror in front of (scope side) the Barlow.

My Saturn from earlier this year was a little weak (noisy) so I'm wanting to see how I can improve it before it is well positioned again.

Obviously, I'm conscious of optical quality too and appreciate my parameters may conflict!