A local saying goes that every fool is different and my folly, as far as scopes are concerned, is the aesthetics of the view.
While out birding yesterday I was able to view a Wood Sandpiper (Tringa glareola) at about 50 m and at 25x through my Kowa 883. As far as I'm concerned, birds don't get any more beautiful than this.
However, scopes are very useful for distant identifications and this is the raison d'etre for many users. It was dull and overcast yesterday and the conditions paradoxically allowed the use of higher magnifications, as the air was stable. I had to crank up the magnification to 60x to id a distant Common Sandpiper in an awkward pose. While zooming back to lower magnifications I passed a point, where there was a fast and significant increase in brightness.
Back home under similar conditions at 6 p.m. I repeated this, zooming back from 60x and consistently reached the point of "enlightenment" around 40x, i.e. 2,2 mm exit pupil.
Coincidentally, this is also the exit pupil size of the 30x W on my ATM 65HD and would roughly correspond to the perceived brightness in the BTX 85 and BTX 95 with their beam splitters at fixed magnifications of 30x and 35x respectively.
I would not dispute the usefulness of exit pupils around 1-1,3 mm and their attendant magnifications, but think perhaps that 2,2 mm is the bottom limit for maintaining terrestrial image "quality".
Comments welcome.
John
While out birding yesterday I was able to view a Wood Sandpiper (Tringa glareola) at about 50 m and at 25x through my Kowa 883. As far as I'm concerned, birds don't get any more beautiful than this.
However, scopes are very useful for distant identifications and this is the raison d'etre for many users. It was dull and overcast yesterday and the conditions paradoxically allowed the use of higher magnifications, as the air was stable. I had to crank up the magnification to 60x to id a distant Common Sandpiper in an awkward pose. While zooming back to lower magnifications I passed a point, where there was a fast and significant increase in brightness.
Back home under similar conditions at 6 p.m. I repeated this, zooming back from 60x and consistently reached the point of "enlightenment" around 40x, i.e. 2,2 mm exit pupil.
Coincidentally, this is also the exit pupil size of the 30x W on my ATM 65HD and would roughly correspond to the perceived brightness in the BTX 85 and BTX 95 with their beam splitters at fixed magnifications of 30x and 35x respectively.
I would not dispute the usefulness of exit pupils around 1-1,3 mm and their attendant magnifications, but think perhaps that 2,2 mm is the bottom limit for maintaining terrestrial image "quality".
Comments welcome.
John