henry link
Well-known member
I had the opportunity yesterday to briefly compare a new Zeiss 8X32 FL to my 8X42 FL. My time at the store was limited so I confined the comparision to the two areas of optical performance that interested me the most between these two binoculars. I felt I could make reasonably accurate judgements about relative light transmission and off-axis sharpness in the 20 minutes I had available. Most of the observations were made in bright sunlight, a few in subdued light inside the store.
Since Zeiss claims that there is less than a 2% difference in light transmission between these two binoculars even though the 32mm uses a Schmidt-Pechan prism and the 42mm an Abbe-Koenig, I was curious to see if I could detect any difference in image brightness in sunlight, where the difference in exit pupil sizes would not be a factor. I know from comparing eyepieces with measured transmission figures that my threshhold for being able to detect any difference at all in light transmission is about 3%. The binoculars were extremely close, but the 8X42 was consistently slightly brighter in sunlight. In a low light area of the store it was substantially brighter. Color transmission appeared to be identical between the two. Contrast in the 32mm was extremely good, roughly equal to the 42mm in sunlight.
From looking at internal views of the FLs' optics on Zeiss websites I suspected that the objective focal ratio of the 32mm might be higher than the 42mm. I wondered whether this could produce better off-axis behaviour in the 32mm. Sure enough, I did observe an improvement in sharpness at the edge of the field in the 32mm (even though it's apparent field is actually a little wider than the 42mm), and more importantly for actual use in the field (provided this aspect of performance matters to you at all) there is clearly some improvement in the area about 10-15 degrees of AFOV away from the center. I would say the off-axis loss of sharpness in the 32mm closely resembles the behavior of the Swarovski 8.5X42 EL, not in the same class as binoculars with field flatteners, but quite good.
The store had a Nikon 8X32 SE and a Swarovski 8X32 EL in stock so I very briefly compared the 8X32 FL to those. The FL was obviously brighter and had better off-axis sharpness than the EL. It appeared about equal to the SE in brightness, but as usual the SE field flattener produced superior off-axis sharpness. I didn't have time or the resolution chart, magnification booster and tripod I would have needed to judge center of the field sharpness, but hand held the 32 FL appeared to have no obvious problems even compared to the 42mm FL.
One curious observation; I noticed that magnification in the 32mm FL appeared a little higher at close distances compared to the 42mm FL. I remembered that AK prisms have a slight off-set like porros, only much less. When I compared the objective spacing of the two I could see that the centers of the 32mm objectives were around 5-10mm closer together than 42mm's at the same IPD setting. A good indication of just how sensitive the eye/brain is to this particular illusion.
Since Zeiss claims that there is less than a 2% difference in light transmission between these two binoculars even though the 32mm uses a Schmidt-Pechan prism and the 42mm an Abbe-Koenig, I was curious to see if I could detect any difference in image brightness in sunlight, where the difference in exit pupil sizes would not be a factor. I know from comparing eyepieces with measured transmission figures that my threshhold for being able to detect any difference at all in light transmission is about 3%. The binoculars were extremely close, but the 8X42 was consistently slightly brighter in sunlight. In a low light area of the store it was substantially brighter. Color transmission appeared to be identical between the two. Contrast in the 32mm was extremely good, roughly equal to the 42mm in sunlight.
From looking at internal views of the FLs' optics on Zeiss websites I suspected that the objective focal ratio of the 32mm might be higher than the 42mm. I wondered whether this could produce better off-axis behaviour in the 32mm. Sure enough, I did observe an improvement in sharpness at the edge of the field in the 32mm (even though it's apparent field is actually a little wider than the 42mm), and more importantly for actual use in the field (provided this aspect of performance matters to you at all) there is clearly some improvement in the area about 10-15 degrees of AFOV away from the center. I would say the off-axis loss of sharpness in the 32mm closely resembles the behavior of the Swarovski 8.5X42 EL, not in the same class as binoculars with field flatteners, but quite good.
The store had a Nikon 8X32 SE and a Swarovski 8X32 EL in stock so I very briefly compared the 8X32 FL to those. The FL was obviously brighter and had better off-axis sharpness than the EL. It appeared about equal to the SE in brightness, but as usual the SE field flattener produced superior off-axis sharpness. I didn't have time or the resolution chart, magnification booster and tripod I would have needed to judge center of the field sharpness, but hand held the 32 FL appeared to have no obvious problems even compared to the 42mm FL.
One curious observation; I noticed that magnification in the 32mm FL appeared a little higher at close distances compared to the 42mm FL. I remembered that AK prisms have a slight off-set like porros, only much less. When I compared the objective spacing of the two I could see that the centers of the 32mm objectives were around 5-10mm closer together than 42mm's at the same IPD setting. A good indication of just how sensitive the eye/brain is to this particular illusion.
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