On Fri, Feb 3, 2012 at 12:40 PM, <jcarman6@q.com> wrote:
Mat, you comments are duly noted. Didn't think about the focal lengths/ratio issue and you've made a good point. The 2" eyepiece in my possession has a 52 degree field and was excellent in the f/10, but it might not be so good at f4.5. DAMN - now I have to build the scope to check it out (thanks Mat ;-))
Joan, it is strictly a focal ratio issue. Remember that you can always stop-down a light bucket to increase the focal ratio, at the expense of aperture, but that alone will tame the coma beast. You can find the largest effective aperture/shortest EFL that yeilds good performance with any given eyepiece. Some nights the seeing won't necessarily support a huge aperture, so it's a legitimate strategy on some occassions. Also, 52 degrees isn't particularly wide, so it just might perform "adequately" at f/4.5, with any coma present not enough to cause bed-wetting issues. I've used a few older design eyepieces at f/4.5 with good results using my old Lumicon coma-corrector. It's given some traditional designs a new lease on life with light-buckets. The Paracorr is probably even better, but I have no personal experience with it. I would suggest that you borrow other club members eyepieces at a star party, and use them in your own scope, before making a purchase. Then you'll know exactly what you'll be getting for your money. I do like Mat's suggestion for super-wide-field eyepieces for high magnification- but for possibly a different reason. On large, undriven scopes, objects stay in the field longer before you have to give the scope a nudge. And that strategy works just as well for planetary viewing too.