henry link
Well-known member
Two friends recently bought binoculars. One got a pair of Eagle Optics 8x32 Rangers for birding and butterfly watching and the other a pair of Leupold 8x30 Yosemites to keep in her van. I volunteered to check out their purchases. Here are the results of the tests I conducted.
Neither binocular had particularly impressive resolution in a boosted magnification test at 64x. The Leupold's resolution was 5.8 arcsec in the left barrel, 6.5 in the right. The Eagle Optics was 5.8 in the left barrel, 7.3 in the right. For comparison I've measured 4.6 arcsec for a Nikon 8x30 E II and 4.1 for a Nikon 8x32 SE in the same test set up.
Both the Yosemite and Ranger showed various defects in an artificial star test at 64x. The Yosemites had some astigmatism and miscollimation in both barrels. The Rangers were worse, with pinching and astigmatism and a seriously miscollimated left barrel. Many binoculars have defects like these which may not cause any visible problems at low magnification, however the problem in the left barrel of the Ranger was bad enough to cause the best sharpness to be skewed slightly to the left of center in the field and that resulted in particularly bad off axis performance in the right half of the field. The astigmatism in the right barrel of the Leupold was bad enough to slightly reduce detail in that side.
Longitudinal CA in both was OK, typical of binoculars with 30/32mm objectives, but both had worse than average lateral color. The Ranger was quite poor, probably the most lateral color I've seen in a binocular, and starting just a few degrees from the center.
Light transmission was good enough in the Ranger, perhaps around 80-85%, and was excellent in the Yosemite, well above 90% and comparable to the very brightest binoculars.
Neither binocular had a very large "sweet spot", by which I mean the central area of critical sharpness. That area in the Yosemite was only about 10-15 degrees wide with a gradual accumulation of astigmatism, lateral color and field curvature beyond that. However, the very center was impressively sharp (in the better barrel). The Ranger was much worse, with a tiny central spot (5-7 degrees) of passable sharpness surrounded by a rapidly deteriorating blur of astigmatism and lateral color (even in the better barrel). The tiny area of decent sharpness in the Ranger makes it a very poor choice for butterflies. Close focus of 3' makes it seem like a good candidate for butterflies, but the eyes are forced to toe in and look very far off axis at such close distances. The off axis performance of the Ranger is so poor that any object visible in both barrels at close range is a hopeless mess. The only way I can imagine looking at butterflies through this binocular is to cover one side and use it as a monocular.
Overall, I found the Yosemite to be quite a nice binocular for $100. In some respects (light transmission, contrast, color accuracy and axial sharpness) it is about as good as any binocular, regardless of cost. It's only real weaknesses are off axis sharpness and lateral color and the loss of sharpness is really no worse than you might expect in a budget binocular. I think the Ranger is not only a pretty bad binocular, but also a pretty bad idea for a binocular. Its designers chose a complex and inherently expensive design (air spaced triplet objective with moving focusing element and Schmidt-Pechan prism) and then tried to execute that design cheaply. It makes much more sense for an inexpensive binocular to start with a simple and inexpensive, but optically respectable design like the Yosemite (cemented doublet objective and Porro prism) and then do that well.
Edit: I forgot to mention a few things about the Yosemite. The clear aperture is not 30mm. It's closer to 27mm, apparently because of an undersized baffle behind the objective. The eye relief is about 18mm measured from the glass of the eylens, but only about 13mm measured from the rim of the fully twisted down eyecup. That would make it marginal for eyeglass wearers. Finally, close focus is not so close, about 11 feet for my eyes.
Neither binocular had particularly impressive resolution in a boosted magnification test at 64x. The Leupold's resolution was 5.8 arcsec in the left barrel, 6.5 in the right. The Eagle Optics was 5.8 in the left barrel, 7.3 in the right. For comparison I've measured 4.6 arcsec for a Nikon 8x30 E II and 4.1 for a Nikon 8x32 SE in the same test set up.
Both the Yosemite and Ranger showed various defects in an artificial star test at 64x. The Yosemites had some astigmatism and miscollimation in both barrels. The Rangers were worse, with pinching and astigmatism and a seriously miscollimated left barrel. Many binoculars have defects like these which may not cause any visible problems at low magnification, however the problem in the left barrel of the Ranger was bad enough to cause the best sharpness to be skewed slightly to the left of center in the field and that resulted in particularly bad off axis performance in the right half of the field. The astigmatism in the right barrel of the Leupold was bad enough to slightly reduce detail in that side.
Longitudinal CA in both was OK, typical of binoculars with 30/32mm objectives, but both had worse than average lateral color. The Ranger was quite poor, probably the most lateral color I've seen in a binocular, and starting just a few degrees from the center.
Light transmission was good enough in the Ranger, perhaps around 80-85%, and was excellent in the Yosemite, well above 90% and comparable to the very brightest binoculars.
Neither binocular had a very large "sweet spot", by which I mean the central area of critical sharpness. That area in the Yosemite was only about 10-15 degrees wide with a gradual accumulation of astigmatism, lateral color and field curvature beyond that. However, the very center was impressively sharp (in the better barrel). The Ranger was much worse, with a tiny central spot (5-7 degrees) of passable sharpness surrounded by a rapidly deteriorating blur of astigmatism and lateral color (even in the better barrel). The tiny area of decent sharpness in the Ranger makes it a very poor choice for butterflies. Close focus of 3' makes it seem like a good candidate for butterflies, but the eyes are forced to toe in and look very far off axis at such close distances. The off axis performance of the Ranger is so poor that any object visible in both barrels at close range is a hopeless mess. The only way I can imagine looking at butterflies through this binocular is to cover one side and use it as a monocular.
Overall, I found the Yosemite to be quite a nice binocular for $100. In some respects (light transmission, contrast, color accuracy and axial sharpness) it is about as good as any binocular, regardless of cost. It's only real weaknesses are off axis sharpness and lateral color and the loss of sharpness is really no worse than you might expect in a budget binocular. I think the Ranger is not only a pretty bad binocular, but also a pretty bad idea for a binocular. Its designers chose a complex and inherently expensive design (air spaced triplet objective with moving focusing element and Schmidt-Pechan prism) and then tried to execute that design cheaply. It makes much more sense for an inexpensive binocular to start with a simple and inexpensive, but optically respectable design like the Yosemite (cemented doublet objective and Porro prism) and then do that well.
Edit: I forgot to mention a few things about the Yosemite. The clear aperture is not 30mm. It's closer to 27mm, apparently because of an undersized baffle behind the objective. The eye relief is about 18mm measured from the glass of the eylens, but only about 13mm measured from the rim of the fully twisted down eyecup. That would make it marginal for eyeglass wearers. Finally, close focus is not so close, about 11 feet for my eyes.
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