Planetary Imaging With A 200p - How Far Can I Push The Zoom?

[Superdavo]

Hello everyone!

While I was out imaging last night, I spent a bit of time thinking about how much I could zoom in with my 200p (or another similar newt). So far, I've managed to reach F/25 (5,000mm), before seeing destroys my images, but I've seen people with telescopes (though often catadioptrics) that are just a couple of inches of aperture larger than mine pushing their scopes to much higher focal lengths.

And so I was wondering, how far can my humble 200p go? 

I think that it would probably be a bit more limited than an SCT of equivalent size - possibly through subtle collimation issues, the effects of diffraction through the spider vanes, and the fact that my scope has a much shorter focal length to begin with (meaning I would need a large - image-degrading - barlow).

So how far do you take it, on a perfect day (if such a thing exists - especially in the UK! )?

David 

[NickK]

Raleigh Law would give you a maximum. Easier to define as a imager but it would be possible to work out using the size of the human rod/cone and the glassware between.

f/64 at 6700mm was too dim looking at the sun for visual but the camera picked up the image on a longer exposure.

f/32 is a good spot - I regularly do 3350mm for planets with a 5x televue on a 670mm fl 4" refractor. 

I'm normally imaging.. but on the odd occasion I'll EP it.