New scope F number question

[coldlegs (Stephen)]

If you were going to build a 10” newt with a conical primary from R.F.Royce that had specs of say ...

“Wavefront accuracy having an RMS of .032 and a Strehl Ratio of .96 or better at 633 nm for apertures up to 10" at f/5 or larger. Mirrors up to 16" and f/5 or larger have a wavefront accuracy having an RMS of .036 and a Strehl Ratio of .94. Mirrors at f/4.5 and lower ratios have correspondingly lower Strehls due to the difficulty of manufacturing fast aspheres.”

and wanted to get the best possible images of Jupiter, Saturn and Mars by chucking a 1.25” X5 powermate (gain X5-7) or a 2” X2 Big Barlow (gain X2-3) on it with a filter wheel and a spc900nc webcam,

what F number would you choose??
Choices are F4.5, 5, 6 and 8.

Cheers
Stephen

[2stroke (Jay)]

With a spc900nc? With planets I guess a higher F as speed wouldn't be and issue, but then if your spending the coin and time i would go a f4.5 for dso. But with a spc900nc which has poor res, small ccd sensor and high noise does it really matter lol. Have you got the spc900nc modded, raw frames and B&W ICX098BL?

[coldlegs (Stephen)]

Originally Posted by 2stroke

With a spc900nc? With planets I guess a higher F as speed wouldn't be and issue, but then if your spending the coin and time i would go a f4.5 for dso. But with a spc900nc which has poor res, small ccd sensor and high noise does it really matter lol. Have you got the spc900nc modded, raw frames and B&W ICX098BL?

Yes it's modded and peltier cooled but for arguments sake let's assume it's a high quality planetary webcam of some sort..i.e. flea3 etc

[2stroke (Jay)]

This may help http://www.eclipsechaser.com/eclink/...smt.htm#expose,
and also this http://www.astrosurf.com/luxorion/report-formulae.htm
I'am to much of a newbie to give a right answere, but logic says you should go for a higher f ratio as its for planets and speed isn't needed as much and the mirrors finish will be better. I would email or phone them and just ask, they may even do a custom to suite your need.

[Poita (Peter)]

I'd be looking at the F8 model.

[Satchmo]

I would recommend F6 as the best balance of tube length and secondary size, ease of collimation etc.