Changing my scope...

[Mr Fiery Jack]

Then I'm curious [genuinely, I'm not trying to be difficult :-) ] why you think a Newtonian is the very worst tool for planetary observing. A well set up Newtonian should be dishing out top views. Plenty of the really hard-core planetary guys in the US are using reflectors for this reason: http://www.cloudynig.../Number/360923/ Now that the crazy sub f/3 Newtonian primaries are appearing in the wild, people are reporting excellent planetary performance from those also: http://www.astromart...?article_id=829

What can I say, I can only speak from my own experiences. I have just come in this minute from my garden, there is some very high cloud but Jupiter as you know is good high. I have both scopes out I collimated the dob as I always do before observing and had it outside for a good two hours before I began. I only ever use a 6mm Radian in the refractor and between this ep and my ED100 its laughs in the face of poor seeing. I tried the Radian in the dob which produced a nice large disc, much larger than the frac. The disc had poor milky detail and was quite wobbly,. The 8mm TV plossl was a little better on Jupiter but now much smaller than the frac, the view still not as clear, down to 11mm, at last the tiny disc was at last on a par with the frac on clarity. I have observed with a group every few weeks for the past two years and have yet to find a Newtonian scope which could match either a very good achro I once owned or the ED. I say Newtonians rather than reflectors as I have seen Mak's that on the night were at least as good and sometimes better as they had a greater resolution. fl 5 do not make good planetary scopes, certainly not in Newtonians' which are always produced in slow focal lengths when made for planetary observation its why some folks mask down their scopes to try to produce the same effect.

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[Mr Fiery Jack]

What can I say, I can only speak from my own experiences. I have just come in this minute from my garden, there is some very high cloud but Jupiter as you know is good high. I have both scopes out I collimated the dob as I always do before observing and had it outside for a good two hours before I began. I only ever use a 6mm Radian in the refractor and between this ep and my ED100 its laughs in the face of poor seeing. I tried the Radian in the dob which produced a nice large disc, much larger than the frac. The disc had poor milky detail and was quite wobbly,. The 8mm TV plossl was a little better on Jupiter but now much smaller than the frac, the view still not as clear, down to 11mm, at last the tiny disc was at last on a par with the frac on clarity. I have observed with a group every few weeks for the past two years and have yet to find a Newtonian scope which could match either a very good achro I once owned or the ED. I say Newtonians rather than reflectors as I have seen Mak's that on the night were at least as good and sometimes better as they had a greater resolution. fl 5 do not make good planetary scopes, certainly not in Newtonians' which are always produced in slow focal lengths when made for planetary observation its why some folks mask down their scopes to try to produce the same effect.

Sorry I forgot to add the views in the refractor tonight were as crisp as they always are. Dobs are great, love em, just not for planets unless the seeing is absolutely perfect, they're just not the right tool for the job.

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[umadog]

I suspect the difference is in our seeing conditions. In the US NE we get the jet stream too, but it seems your conditions sound more turbulent and that will hit the bigger scope hard. What's the maximum power you use on good night? It sounds like you're at about 150 x on the refractor and the 10" is only looking good at about 110x. So if that's the most the sky will support then, yes, we have different seeing conditions. Where I observe it's fairly common for a 10" to take 200x.

In bad conditions I get better views with the 18" stopped down to 7". Star balloon up to fuzzy balls and looks awful. However, on nights when I can get stable views at >200x, the big Newt works better without the aperture mask. At 250x there's more detail on Jupiter than I can take in and and the purple streaks on the equator are prominent. I've once got 420x. For reference, down in Florida they're hitting 1000x with the big scopes (so they say, anway...). Pretty crazy.

It's certainly true that smaller apertures show seeing issues less, but I don't think it's focal ratio related. Only aperture is in the equations: www.telescope-optics.net/seeing_and_aperture.htm The long focal ratio Newts were made to decrease the effect of the central obstruction and so decrease diffraction. If you stopped down the Newt to 100mm you should see roughly what the ED shows, no? Although you may have more thermal issues so it's unlikely to be quite as good.