90 mm f/10 decent?

I have a 10" dob but am lookin for a smaller refractor for planets and the moon. Would the orion 90mm f/10 be a decent choice or would it not be any better than my dob for the planets? Orion has got it on sale for $249
thx
Brian

Your 10" Dob should bury ANY 90mm scope on the planets if it is cooled and collimated. Of course a lot depends on the quality of the primary mirror (and secondary mirror for that matter). If you're not an ace at collimation, learn the ins and outs of collimation. It will be cheaper than a scope purchase and more rewarding. If you are an ace at collimation already and you're still not satisfied with the Newt, try an off-axis aperture mask, i.e. make a piece of cardboard to cover your scope's aperture. Then cut a hole off to the side of about 4" diameter, maybe a little less depending on the size of your secondary mirror, and position the mask so that looking through this hole you don't see either the secondary mirror or any spider vanes. Here is a very fancy example that is made to also hold a solar filter (just forget about the filter).

http://www.teleporttelescopes.com/Access/10MasFilNew.jpg

With the mask in place, your scope is now an unobstructed, off-axis Newtonian. Technically there is a tweak you might make to the collimation from this point, but it should be darn good if the scope is in collimation without the mask.
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Mike

Attached Image:

The 90mm will be great for those hazy or not-so-great nights when the 10 inch can't live up to its full potential anyway, and you may not feel like lugging the darn thing around and waiting for it to cool. I don't have experience with that specific model, but as Jim G. indicates it seems like a decent scope.

As a concrete example of "better image quality" that Jim G. mentions, my 6 inch reflector will walk all over my 70mm refractor pretty much any night...BUT, take for example Castor. In my 70mm, it's a lovely sight almost any night, barring the absolute worst conditions. Tight, but nice. My 6 inch will always split Castor, but in non-steady skies the little star images may be crawling all over the place, without any diffraction rings, etc. So while my bigger scope isn't performing any *worse*, technically, than the little guy, the little guy's image just plain looks nicer.

So I think the 90mm would be an excellent complement to your dob.

I have a 10" newtonian and an 80mm apo refractor. The 10" will handily beat the 80mm on the planets on any night when the planets are worth observing. The 10" does need to be cooled down and collimated properly. I do prefer the views through the refractor for double stars on all but the most stable nights and for low to middle power observing of the moon (higher contrast image). The refractor also serves as my daytime terrestrial and solar scope. If you want the extra versatility of a refractor I'd say go for it, just don't expect it to outperform a collimated 10" dob (with good optics).

Clear Skies,

Joplin