henry link
Well-known member
I recently spent a week birding on the Outer Banks of North Carolina. While there I ran into a birder who uses nothing but Zeiss optics for birding. She has a very nice collection of Zeiss binoculars going back to the Dialyts, including an 8x42 HT and an 8x42 SF. I was able to spend a little time with the SF and she was kind enough to lend me her HT for a day.
My time with the SF was so short that I decided to limit myself to evaluating its distortion profile since there has been some disagreement here about how much “rolling ball” it displays compared to the Swarovski SV. I don’t want to make too big an issue of distortion since most people can probably adjust to a wide range of possible distortions, but if the subject is going to be discussed at all the first thing up should be to accurately establish what kind of distortion is there. For that purpose I used two targets that happened to be handy: a tall antenna that allowed me to see the behavior of a straight vertical line as it moves across the FOV and a small circular object that allowed me to observe how shapes change as they move from the center to the edge.
When I panned those objects through the FOV what I saw was pronounced “mustache” distortion. Approximately the inner 75% of the field developed strong pincushion distortion. In the outer 25% the pincushion straightened out and to my eyes actually reversed to slight barrel distortion in the last few degrees of apparent field. That distortion pattern caused the vertical line to curved back and forth several times as it moved from edge to center to edge. When the small circle was moved from the center to 3:00 on the edge it first stretched into a horizontal oval at about 65-75% (indicating pincushion so strong that it overcorrects angular magnification distortion). Then it became a circle again over a narrow angle. Then it compressed into a vertical oval at the very edge. Swarovski SVs do something similar, but the SVs I’ve seen have milder pincushion in the inner field (about enough to correct AMD), which then transitions to something like zero rectilinear distortion at the edge, not quite reaching barrel distortion. Given the pattern I observed in the SF I’m not at all surprised to read opinions here that it has stronger “rolling ball” than the SV. Other reports here of higher pincushion in the SF compared to the SV and implying lower rolling ball also appear to be correct at far as they go, but left out is the essential information that the distortion reverses in the outer part of the field. From what I’ve seen I think, for those who are susceptible, the complex distortions in the SV and SF are more likely to cause some kind of visual disturbance when panning than the simple solution of applying a small amount of straightforward pincushion, just enough so that both pincushion and angular magnification distortion are unobtrusive.
I didn’t have time for a close look at other qualities and besides I doubted that the optics were completely clean (tough to keep optics clean in the salt spray and wind of the Outer Banks), so I didn’t form any other opinions about the SF.
Now on to the HT.
Since I was away from home I had to improvise some test set-ups. I used the glitter point of the sun from a small metal ball on top of a pepper grinder as an artificial star and I had to fall back on Steven Ingraham’s “Dollar Bill Test” to roughly compare the HT’s unboosted resolution in sunlight to my 8x56 FL. I couldn’t do any tests with reduced apertures and color bias was the only thing I could photograph.
First I compared the reflection patterns returning from the HT lens elements to the reflections coming from my wife’s 8x42 FL. The patterns appeared to be more or less identical, so I would say there has been little if any change to the basic optical formula between these two 8x42 models. Further evidence for no change came from star-tests (at 64x) showing the axial aberrations of the FL and HT to be as similar as I would expect to see between two samples of the same model. Both showed spherical overcorrection. Overcorrection is unusual in binoculars, which are typically undercorrected. The right side of the HT had no other significant defects, but the left side was moderately comatic, probably because collimation required the application of a fair amount of eyepiece eccentricity. I also observed an identical mix of off-axis aberrations, dominated by astigmatism. The off-axis performance was so similar between the two binoculars that I really couldn’t tell them apart. Distortion also appeared to be identical, consisting of the same amount of simple pincushion in both.
I could see a slight increase in brightness in the HT, but no significant difference in color bias compared to this early production 8x42 FL from 2004. On the other hand I did seem to see an improvement in color bias over my 2007 8x56 FL, which probably reflects the increasing green/yellow bias I’ve observed in later FLs compared to early ones. The images below show the difference between the 8x56 FL and 8x42 HT when they were placed in front of a white surface in sunlight. The right Powerpoint image was made by taking crops of the areas within the binocular field stops in the left photo and placing them together over a crop of the background. I was surprised to see the mild blue bias of the HT in the photo, which I didn’t notice visually.
Since we were staying in a house right on the Pamlico Sound I had ample opportunities to induce glare from both direct sun and reflections from water. The extra objective baffle in the HT seemed to slightly improve its glare resistance in bright light compared to the 8x42 FL, but the big exit pupil of the 8x56 was even more effective at keeping glare out of the eye under the same conditions. Sorry to say I forgot to check glare resistance under twilight conditions when the HT’s baffle might make more difference.
Overall the change from the 8x42 FL to the 8x42 HT strikes me as very much like the change from the Leica Trinovid to the Ultravid: essentially the optics from an earlier model have transplanted into a new body with some small improvements to light transmission, color bias and glare resistance. The basic aberrations, both on and off axis, remain as they were.
The rest of the time I had with the HT was spent comparing its image quality to my 8x56 FL, since that’s the one I would replace with any new binocular. The big FL is my reference for a binocular image with very low axial aberrations. In the dollar bill test, with the binos tripod mounted in sunlight, I needed to move the HT about 8 inches closer to the bill in order to resolve the lines under the “ONE” and even then best focus had the slightly gauzy look I associate with a little too much spherical aberration. Later, when observing a gibbous moon the 8x56 always produced an obviously sharper, cleaner and more relaxed image. Several other targets produced the same result, a better image through the FL that was easy to see. All comparisons were done using both eyes and also using only one eye through the right (best) side of both binoculars. The only areas where I found the HT superior to the 8x56 FL were the more neutral color bias and a very slight increase in brightness. For me those improvements don’t compensate for a more highly aberrated image.
In the end, it doesn’t look like either of these new Zeiss models is a candidate to replace my 8 year old 8x56 FL. I suppose I’m just stuck with the hefty FL for as long as I continue to see a better image through it than I do through other binoculars. It’s a shame Zeiss didn’t just give the 8x56 FL more neutral coatings and HT glass to turn it into an 8x56 HT. The 8x54 HT I tried last year was a disappointing step backward and since the Swaro 8x56 SLC is unavailable in the US to audition I guess for now my binocular money will stay in my pocket.
Henry Link
My time with the SF was so short that I decided to limit myself to evaluating its distortion profile since there has been some disagreement here about how much “rolling ball” it displays compared to the Swarovski SV. I don’t want to make too big an issue of distortion since most people can probably adjust to a wide range of possible distortions, but if the subject is going to be discussed at all the first thing up should be to accurately establish what kind of distortion is there. For that purpose I used two targets that happened to be handy: a tall antenna that allowed me to see the behavior of a straight vertical line as it moves across the FOV and a small circular object that allowed me to observe how shapes change as they move from the center to the edge.
When I panned those objects through the FOV what I saw was pronounced “mustache” distortion. Approximately the inner 75% of the field developed strong pincushion distortion. In the outer 25% the pincushion straightened out and to my eyes actually reversed to slight barrel distortion in the last few degrees of apparent field. That distortion pattern caused the vertical line to curved back and forth several times as it moved from edge to center to edge. When the small circle was moved from the center to 3:00 on the edge it first stretched into a horizontal oval at about 65-75% (indicating pincushion so strong that it overcorrects angular magnification distortion). Then it became a circle again over a narrow angle. Then it compressed into a vertical oval at the very edge. Swarovski SVs do something similar, but the SVs I’ve seen have milder pincushion in the inner field (about enough to correct AMD), which then transitions to something like zero rectilinear distortion at the edge, not quite reaching barrel distortion. Given the pattern I observed in the SF I’m not at all surprised to read opinions here that it has stronger “rolling ball” than the SV. Other reports here of higher pincushion in the SF compared to the SV and implying lower rolling ball also appear to be correct at far as they go, but left out is the essential information that the distortion reverses in the outer part of the field. From what I’ve seen I think, for those who are susceptible, the complex distortions in the SV and SF are more likely to cause some kind of visual disturbance when panning than the simple solution of applying a small amount of straightforward pincushion, just enough so that both pincushion and angular magnification distortion are unobtrusive.
I didn’t have time for a close look at other qualities and besides I doubted that the optics were completely clean (tough to keep optics clean in the salt spray and wind of the Outer Banks), so I didn’t form any other opinions about the SF.
Now on to the HT.
Since I was away from home I had to improvise some test set-ups. I used the glitter point of the sun from a small metal ball on top of a pepper grinder as an artificial star and I had to fall back on Steven Ingraham’s “Dollar Bill Test” to roughly compare the HT’s unboosted resolution in sunlight to my 8x56 FL. I couldn’t do any tests with reduced apertures and color bias was the only thing I could photograph.
First I compared the reflection patterns returning from the HT lens elements to the reflections coming from my wife’s 8x42 FL. The patterns appeared to be more or less identical, so I would say there has been little if any change to the basic optical formula between these two 8x42 models. Further evidence for no change came from star-tests (at 64x) showing the axial aberrations of the FL and HT to be as similar as I would expect to see between two samples of the same model. Both showed spherical overcorrection. Overcorrection is unusual in binoculars, which are typically undercorrected. The right side of the HT had no other significant defects, but the left side was moderately comatic, probably because collimation required the application of a fair amount of eyepiece eccentricity. I also observed an identical mix of off-axis aberrations, dominated by astigmatism. The off-axis performance was so similar between the two binoculars that I really couldn’t tell them apart. Distortion also appeared to be identical, consisting of the same amount of simple pincushion in both.
I could see a slight increase in brightness in the HT, but no significant difference in color bias compared to this early production 8x42 FL from 2004. On the other hand I did seem to see an improvement in color bias over my 2007 8x56 FL, which probably reflects the increasing green/yellow bias I’ve observed in later FLs compared to early ones. The images below show the difference between the 8x56 FL and 8x42 HT when they were placed in front of a white surface in sunlight. The right Powerpoint image was made by taking crops of the areas within the binocular field stops in the left photo and placing them together over a crop of the background. I was surprised to see the mild blue bias of the HT in the photo, which I didn’t notice visually.
Since we were staying in a house right on the Pamlico Sound I had ample opportunities to induce glare from both direct sun and reflections from water. The extra objective baffle in the HT seemed to slightly improve its glare resistance in bright light compared to the 8x42 FL, but the big exit pupil of the 8x56 was even more effective at keeping glare out of the eye under the same conditions. Sorry to say I forgot to check glare resistance under twilight conditions when the HT’s baffle might make more difference.
Overall the change from the 8x42 FL to the 8x42 HT strikes me as very much like the change from the Leica Trinovid to the Ultravid: essentially the optics from an earlier model have transplanted into a new body with some small improvements to light transmission, color bias and glare resistance. The basic aberrations, both on and off axis, remain as they were.
The rest of the time I had with the HT was spent comparing its image quality to my 8x56 FL, since that’s the one I would replace with any new binocular. The big FL is my reference for a binocular image with very low axial aberrations. In the dollar bill test, with the binos tripod mounted in sunlight, I needed to move the HT about 8 inches closer to the bill in order to resolve the lines under the “ONE” and even then best focus had the slightly gauzy look I associate with a little too much spherical aberration. Later, when observing a gibbous moon the 8x56 always produced an obviously sharper, cleaner and more relaxed image. Several other targets produced the same result, a better image through the FL that was easy to see. All comparisons were done using both eyes and also using only one eye through the right (best) side of both binoculars. The only areas where I found the HT superior to the 8x56 FL were the more neutral color bias and a very slight increase in brightness. For me those improvements don’t compensate for a more highly aberrated image.
In the end, it doesn’t look like either of these new Zeiss models is a candidate to replace my 8 year old 8x56 FL. I suppose I’m just stuck with the hefty FL for as long as I continue to see a better image through it than I do through other binoculars. It’s a shame Zeiss didn’t just give the 8x56 FL more neutral coatings and HT glass to turn it into an 8x56 HT. The 8x54 HT I tried last year was a disappointing step backward and since the Swaro 8x56 SLC is unavailable in the US to audition I guess for now my binocular money will stay in my pocket.
Henry Link
