Quote:
Originally Posted by MichaelWB
Hi Joe.
Your critique is freely accepted. I am more than happy to accede to others with much wider knowledge than me. The reason I said that it would have the widest fov is that on my Plossl the eyepiece id is 47mm and the field stop is over 43mm id, over 90% of possible available fov. Not the widest possible, but substantial all the same. All the other info you supply is well outside my expertise. Thanks for your enlightenment
|
Hi Michael,
The critical difference is that your scope is F7.2; while the original posters is F5. The 55mm eyepiece is only giving an exit pupil of 7.6mm in your F7.2 scope, which is slightly oversized, but still workable without too much light loss. It's a general rule of thumb that you shouldn't use an eyepiece that gives an exit pupil > 7mm, as that is the approximate maximum eye pupil dilation of a young healthy adult. As we get older, our maximum pupil dilation reduces. Unfortunately, the same 55mm eyepiece in an F5 scope (regardless of aperture) is giving an 11mm exit pupil, which is way oversized with significant light loss. While the view may "appear" decent, the light loss would reduce the effective scope aperture from 12" to the equivalent of somewhere between an 8" and 10" scope.
Cheers
John B