A recent mission I've been on with binoculars has been watching eagles fly,
especially when they ride the highway and cloverleaf thermals. This involves
great distances, on the order of 1000 to 6000 ft. I had some luck adding a little
detail with a 10x50 and then 20x80 binoculars, but I noticed the real resolution
wasn't keeping pace. After checking the methods for finding resolution used
by a few experts,
http://www.cloudynights.com/ubbarch...ge/0/view/collapsed/sb/5/o/all/fpart/all/vc/1
http://birdforum.net/showthread.php?t=120290
(EdZ and Henry Link)
I adopted the method of using the 6x16 monocular EdZ used, to more clearly
see the target, and decided a light fixture and fonts at 37 ft. were more than adequate
for ballparking the issue. When it became clear 7x, 8x, 10x, and 20x binoculars all
clustered around the same real resolution (some like the Swift/Audubon 8.5x44 being
sharper than most on a 0.07" font), I checked into some pictures taken with spotters
and got ahold of a Swift Searcher, Model 839, which claims:
"Here is a superior spotting scope with high resolving telephoto capabilities.
The Searcher's three lens, triple achromatic objectice and orthoscopic eyepieces
create maximum resolution in a compact body..."
The eyepieces aren't remarkable compared to binoculars, but
it operates at an f/D ratio of 6.5, nearly twice that of most binoculars.
Then there is that mysterious 3-element achromat.
Testing the spotter at the same distance revealed much sharper edges (at 20x),
and testing it at 3 times the distance showed edges still sharper than the best
binoculars at 37 ft. This is the way to go for resolution.
Next, it was off to the thermals. There was a lot more detail to be seen.
It didn't pick up much blur at 40x, but that is a slightly tricky power
for tracking. Clearly, I need to break the f-ratio rules for binoculars.
The 20x astros were particulary disappointing. Maybe the super astros
are sharp enough, but they are in the thousands of dollars and dozens
of pounds weight.
So....I was thinking, I could collimated two of these things (spotters) at 20x.
Result: great eagle binoculars.
However, I am wondering whether there is anything to be gained by
stereo paths at 1000 or 5000 ft. At some ratio of distance over
objective spacing it seems the 3D benefits would fizzle.
There is the optic cortex to consider, noise and all, but
physically and financially it seems better to have a single 80mm ~f/6-8
barrel with a binocular viewing splitter (as an upgrade to this).
What good would a second barrel be at these distances?
especially when they ride the highway and cloverleaf thermals. This involves
great distances, on the order of 1000 to 6000 ft. I had some luck adding a little
detail with a 10x50 and then 20x80 binoculars, but I noticed the real resolution
wasn't keeping pace. After checking the methods for finding resolution used
by a few experts,
http://www.cloudynights.com/ubbarch...ge/0/view/collapsed/sb/5/o/all/fpart/all/vc/1
http://birdforum.net/showthread.php?t=120290
(EdZ and Henry Link)
I adopted the method of using the 6x16 monocular EdZ used, to more clearly
see the target, and decided a light fixture and fonts at 37 ft. were more than adequate
for ballparking the issue. When it became clear 7x, 8x, 10x, and 20x binoculars all
clustered around the same real resolution (some like the Swift/Audubon 8.5x44 being
sharper than most on a 0.07" font), I checked into some pictures taken with spotters
and got ahold of a Swift Searcher, Model 839, which claims:
"Here is a superior spotting scope with high resolving telephoto capabilities.
The Searcher's three lens, triple achromatic objectice and orthoscopic eyepieces
create maximum resolution in a compact body..."
The eyepieces aren't remarkable compared to binoculars, but
it operates at an f/D ratio of 6.5, nearly twice that of most binoculars.
Then there is that mysterious 3-element achromat.
Testing the spotter at the same distance revealed much sharper edges (at 20x),
and testing it at 3 times the distance showed edges still sharper than the best
binoculars at 37 ft. This is the way to go for resolution.
Next, it was off to the thermals. There was a lot more detail to be seen.
It didn't pick up much blur at 40x, but that is a slightly tricky power
for tracking. Clearly, I need to break the f-ratio rules for binoculars.
The 20x astros were particulary disappointing. Maybe the super astros
are sharp enough, but they are in the thousands of dollars and dozens
of pounds weight.
So....I was thinking, I could collimated two of these things (spotters) at 20x.
Result: great eagle binoculars.
However, I am wondering whether there is anything to be gained by
stereo paths at 1000 or 5000 ft. At some ratio of distance over
objective spacing it seems the 3D benefits would fizzle.
There is the optic cortex to consider, noise and all, but
physically and financially it seems better to have a single 80mm ~f/6-8
barrel with a binocular viewing splitter (as an upgrade to this).
What good would a second barrel be at these distances?
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