fast scopes and planetary viewing

Hi - I have a 10" Newtonian dob (f/4.5). I've been reading that slower scopes (> f/6) are better for viewing solar system objects. I haven't found an explanation for this. Can someone explain this to me or point me somewhere where I can read about it, preferably written so that a 5-year-old can understand it.

Thanks!
Joe

Joe Sgambellone said:

Hi - I have a 10" Newtonian dob (f/4.5). I've been reading that slower scopes (> f/6) are better for viewing solar system objects. I haven't found an explanation for this. Can someone explain this to me or point me somewhere where I can read about it, preferably written so that a 5-year-old can understand it.

Thanks!
Joe

The main reason? It's easier to get higher magnification for planetary work with longer more comfortable to use eyepiece focal lengths.

OTOH, you can just use a barlow with an eyepiece on a faster scope.

Some people thing that slower mirrors are easier to make very well. The opposite is actually the case.

Joe, another, minor, advantage to slower scopes is that classic eye piece designs can work well with them. I've read lots of posts by hard core planetary observers about their orthoscopic and monocentric eye pieces. Some of these eye piece designs have only a few elements and thus are capable of low light loss and scatter which improves resolution of small and low-contrast details.

Somewhat related: one of my favorite eye pieces is an Orion Optiluxe 40mm. It produces wonderful images in my 6" f/12 refractor, but terrible flocks of seagulls in my friend's 12.5" f/4.5 Newtonian (even with a Paracorr).