Quote:
Originally Posted by brian nordstrom
 Steve yes in all that is true , but my 27mm 2inch Panoptic is much better than both my 25 and 32mm TV plossls |
I qualified my statement by saying "all else being equal ... etc". For example, if you replace your premo 32mm 1.25" Plossl with another premo 32mm 2" Plossl it won't make any difference. (Although TV plossls are not a good example because they all vignette a little at any FL -
I'm sure there is a good design compromise reason for that.)
I could quantify what I said earlier with formulas but the maths gets a little ugly and there is an easier way. Look at the true specs of the EP: the apparent field of view and the focal length. If these are the same for a 1.25" and a 2" EP, the barrel size won't make a difference.
But in the end it's still all just academic/nerdy stuff, because an EP typically will only have a 2" barrel if its design specs don't physically fit into a 1.25" barrel. You'll never find a 27mm 68-degree AFOV EP like a Pano with a 1.25" barrel and I've never come across a <=30mm 2" Plossl either. So, simply judge the EP for what it does and forget about the barrel size...
... except there is one reason why barrel size matters: convenience. Given your observing habits, how often will you have to swap out that 2"-to-1.25" adapter?