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Old Monday 4th September 2017, 19:58   #1
james holdsworth
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Does the 8x42 HT have ''significant astigmatism''?

I hate to dig up this old chestnut again but I'm just flummoxed by comments made recently, and in several threads, by Alexis Powell that the 42 mm HT's have ''significant astigmatism.''

Now then, the vast majority of users have commented that edge sharpness / or sweetspot size in the HT was better than the FL. Many users seemed to have little comment on these aspects, suggesting that they either didn't care or it didn't present itself as a problem. There were exceptions - some saw an overly small sweetspot, Henry thought the optics and aberration pattern nearly identical to the FL and I recall two users that noted unacceptable astigmatism.

To me, I see a big sweetspot - like twice the size of my 10x42 FL and much improved edge sharpness, especially in the lower half of the FOV.

So, what's the reality? Am I just a brand homer glossing over the faults on his expensive toy? Are my eyes and technical abilities just not able to detect this astigmatism...or, does the HT actually have the improved optical qualities that I [and most users] seem to see?

Attached are a series of photos taken from my backyard - note these were handheld, focus [even in the centre] could likely be improved and ignore the alignment as they are all a bit off. Still, I wanted a target that showed well the outer 2/3rds of the FOV, including the quality of the outer 10% or so as well as illustrating the extent of image degradation off-centre. Target was est. 100 m distant, lighting very harsh and it was windy, so branches moving a bit which might blur the very tips.

So I see sharpness extending well out from centre, almost no image loss at 12 / 3 / 6 or 9 o' clock, even at the very edge, and very little or almost no astigmatism - certainly not significant in any way. Feel free to zoom in on them, to the limit of resolution - I needed to resize significantly to get them to fit.

Am I doing this wrong? Are my impressions off-base? What are the opinions of the forumers here? Remember, these were hand-held and are not perfect but [to me] seem representative to what I see in the field.
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Old Monday 4th September 2017, 20:03   #2
james holdsworth
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Crap, the re-sized images all look far softer than the larger originals - any way to post larger images?

I can e-mail the originals to any that want them, although I had hoped all could view them...at any rate, I still think you can see the consistency of sharpness throughout the FOV, even if the entire image is less sharp than my originals.
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Old Monday 4th September 2017, 20:28   #3
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James, if you look at the Allbino's tests of the Zeiss FL and the HT, in the 10x42, they found
the FL corrected astigmatism a bit better than the HT.

That may be the main thing why it scored less than the FL.

They have not tested the 8x42 HT.

I am not familiar with how astigmatism is tested, but they mention pinpoint star images.

Jerry
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Old Monday 4th September 2017, 20:34   #4
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Originally Posted by NDhunter View Post
James, if you look at the Allbino's tests of the Zeiss FL and the HT, in the 10x42, they found
the FL corrected astigmatism a bit better than the HT.

That may be the main thing why it scored less than the FL.

They have not tested the 8x42 HT.

I am not familiar with how astigmatism is tested, but they mention pinpoint star images.

Jerry
Thanks Jerry, I think I'll leave Allbinos out of this as they seem to define astigmatism differently than to what Alexis is referring - which I assume is the inability to focus both the edge and centre of the FOV at the same time.

I'm still interested in other user / owners opinion on what they see in their units, compared to the FL or their bin of choice.
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Old Monday 4th September 2017, 20:47   #5
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Originally Posted by james holdsworth View Post
Thanks Jerry, I think I'll leave Allbinos out of this as they seem to define astigmatism differently than to what Alexis is referring - which I assume is the inability to focus both the edge and centre of the FOV at the same time.

I'm still interested in other user / owners opinion on what they see in their units, compared to the FL or their bin of choice.
Almost, but not quite. If the fuzzy edge can be brought into focus (at the expense of center sharpness), then the problem is field curvature. If it can not be brought into focus the problem is astigmatism. The only way the center and edge could be simultaneously in focus is if astigmatism and field curvature were both eliminated.

Ed
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Old Monday 4th September 2017, 21:31   #6
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James,

Your message box is full.

Ed
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Old Monday 4th September 2017, 21:35   #7
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Dear James,

When I say that the FL and HT have significant astigmatism, I mean that they show it very prominently (to my eye/brain) compared to other premium bins. It is, for me, those models' most significant weakness, and since I find it irritating, I think of it whenever I consider their merits. Analogously, the Leica Ultravid models, even the latest versions, have more CA than other premium bins, so that is the deficiency I think of first with them. All in all, these bins are all superb tools. The Zeiss 8x32 FL is my favored travel and butterflying+birding binocular, so I use it quite a lot, despite its astigmatism. And I do appreciate its flat field and very very low CA. Its centerfield sharpness/clarity is so good that I don't feel that it holds me back when pushing the limits of my visual acuity looking at distant apparently tiny subjects, unlike some other 8x32. But I am really not a fan of astigmatism, preferring curvature of field if given a choice for the cause of off-axis performance loss. I didn't replace my Zeiss 7x42 BGATP with the FL when it became available, because to my eye the latter has a more astigmatic, even though flatter, field.

I'm not sure how well your tree pictures are going to allow assessment of astigmatism, even in larger size. I suggest you instead take some pictures of fine screening, or a rough cloth like burlap, and take pics with the focus jiggled one way versus the other of what is perfect for the center field. That exercise generally reveals astigmatism very easily, as you will see that outside the central sweet spot that horizontal and vertical lines (or, more precisely, radial versus tangential lines) increasingly do not come into sharp focus together, and that when the center is in perfect focus, the edge will be in-between best settings for horizontal versus vertical lines.

--AP

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Old Monday 4th September 2017, 22:24   #8
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Old Monday 4th September 2017, 22:30   #9
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Originally Posted by Alexis Powell View Post
Dear James,

When I say that the FL and HT have significant astigmatism, I mean that they show it very prominently (to my eye/brain) compared to other premium bins. It is, for me, those models' most significant weakness, and since I find it irritating, I think of it whenever I consider their merits. Analogously, the Leica Ultravid models, even the latest versions, have more CA than other premium bins, so that is the deficiency I think of first with them. All in all, these bins are all superb tools. The Zeiss 8x32 FL is my favored travel and butterflying+birding binocular, so I use it quite a lot, despite its astigmatism. And I do appreciate its flat field and very very low CA. Its centerfield sharpness/clarity is so good that I don't feel that it holds me back when pushing the limits of my visual acuity looking at distant apparently tiny subjects, unlike some other 8x32. But I am really not a fan of astigmatism, preferring curvature of field if given a choice for the cause of off-axis performance loss. I didn't replace my Zeiss 7x42 BGATP with the FL when it became available, because to my eye the latter has a more astigmatic, even though flatter, field.

I'm not sure how well your tree pictures are going to allow assessment of astigmatism, even in larger size. I suggest you instead take some pictures of fine screening, or a rough cloth like burlap, and take pics with the focus jiggled one way versus the other of what is perfect for the center field. That exercise generally reveals astigmatism very easily, as you will see that outside the central sweet spot that horizontal and vertical lines (or, more precisely, radial versus tangential lines) increasingly do not come into sharp focus together, and that when the center is in perfect focus, the edge will be in-between best settings for horizontal versus vertical lines.

--AP
OK, so how does the phenomena you describe manifest itself in the field, as in, during the course of birding etc? If I can view from 100 m and most of the field is sharp, what am I missing? I did take pictures from 8 m of a calendar and find that, again, most of the field is sharp [pic. available]. So, near and far, most of the field is sharp, the sweetspot is large and the edges are nearly as sharp as the centre. What more does one ask for?

Where is the ''significant'' or ''lots'' of astigmatism? Where is the ''small'' sweetspot - wouldn't some of that show in photos? Even if the pics are not super-sharp, to me it is easy to see the decline in sharpness from centre to edge is gradual and minimal, central area of sharpness is similar until well out to the edge, and the edges are all use-ably sharp.
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Old Tuesday 5th September 2017, 02:08   #10
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OK, so how does the phenomena you describe manifest itself in the field, as in, during the course of birding etc? If I can view from 100 m and most of the field is sharp, what am I missing? I did take pictures from 8 m of a calendar and find that, again, most of the field is sharp [pic. available]. So, near and far, most of the field is sharp, the sweetspot is large and the edges are nearly as sharp as the centre. What more does one ask for?

Where is the ''significant'' or ''lots'' of astigmatism? Where is the ''small'' sweetspot - wouldn't some of that show in photos? Even if the pics are not super-sharp, to me it is easy to see the decline in sharpness from centre to edge is gradual and minimal, central area of sharpness is similar until well out to the edge, and the edges are all use-ably sharp.
If it doesn't bother you, if it doesn't present itself to you as a visual distraction, it isn't a problem. Really, don't worry about it. I've used, and continue to use, plenty of bins that are not sharp edge to edge, and they work fine. But I have a habit (as you likely know from my previous posts on Birdforum) of darting my eyes around the view. Consequently, I find bins that are sharp edge to edge more relaxing to use. I liked my Nikon 8x40 DCF Classic Eagle for that reason, I liked the view through the Nikon 8x32 SE, and nowadays I enjoy the Swarovski 8.5x42 EL SV. One way this presents itself interactively with my style of birding is that e.g. when trying to see birds in dense vegetation (e.g. sparrows in brush or grass, wood warblers in trees), I have a habit of looking to where I last saw the bird, keeping the bins locked on that spot (at the center of the view) in case the bird reappears in the same place, but then begin looking around the view for other things. When using a bin with low astigmatism and field curvature, I can make small adjustments to the focus to make the view clear wherever I look. When a bin has astigmatism, those efforts to correct the focus are futile. That's just one example of why I often find myself looking at things off axis.

I think that another reason that astigmatism bothers me is that I am constantly (obsessively?) adjusting the focus of my bins while using them, and I pay attention to the quality of the whole field as it comes in and out of focus. I find the visual effects of astigmatism when rocking the focus especially annoying, as what should be simultaneously sharp perpendicular edges get smeared first one way, then the other.

The astigmatism of the HT is a fact, but whether it is a problem is for the user to decide.

--AP
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Old Tuesday 5th September 2017, 03:08   #11
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It is an individual user issue.

I have a Zeiss 7x42 Victory FL which has about an 8.5 FOV. It has astigmatic edges I am told. I don't notice them at all.

Bob

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Old Tuesday 5th September 2017, 05:02   #12
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If it doesn't bother you, if it doesn't present itself to you as a visual distraction, it isn't a problem. Really, don't worry about it. I've used, and continue to use, plenty of bins that are not sharp edge to edge, and they work fine. But I have a habit (as you likely know from my previous posts on Birdforum) of darting my eyes around the view. Consequently, I find bins that are sharp edge to edge more relaxing to use. I liked my Nikon 8x40 DCF Classic Eagle for that reason, I liked the view through the Nikon 8x32 SE, and nowadays I enjoy the Swarovski 8.5x42 EL SV. One way this presents itself interactively with my style of birding is that e.g. when trying to see birds in dense vegetation (e.g. sparrows in brush or grass, wood warblers in trees), I have a habit of looking to where I last saw the bird, keeping the bins locked on that spot (at the center of the view) in case the bird reappears in the same place, but then begin looking around the view for other things. When using a bin with low astigmatism and field curvature, I can make small adjustments to the focus to make the view clear wherever I look. When a bin has astigmatism, those efforts to correct the focus are futile. That's just one example of why I often find myself looking at things off axis.

I think that another reason that astigmatism bothers me is that I am constantly (obsessively?) adjusting the focus of my bins while using them, and I pay attention to the quality of the whole field as it comes in and out of focus. I find the visual effects of astigmatism when rocking the focus especially annoying, as what should be simultaneously sharp perpendicular edges get smeared first one way, then the other.

The astigmatism of the HT is a fact, but whether it is a problem is for the user to decide.

--AP
I guess it shouldn't be too surprising that one's instrument preferences are mated to one's viewing style. In this instance I'm the logical opposite, because my head/body quickly follow my eyes in such a way that the edges rarely come into view. Thus centered, I expect the periphery to approximate my unaided, i.e., natural, visual field curvature, rather than be artificially flattened, — as with an SE or SV.

Certainly astigmatism never helped anyone, but 'natural' field curvature still allows peripheral objects to appear in focus, though obviously not all on the same (flat) object plane. In my opinion, this creates the best conditions for an ideal immersive view hallmarked by perceptual 'presence.' Fortunately, the 804 Audubon, Swaro SLC-HD, and Leica BR have minimal astigmatism and well-corrected field curvature, making them very easy viewing in the field. Flat field binoculars induce what I can only describe as very distracting 'cardboard' image perceptions.

There's no right or wrong, it's all in how one prefers to use 'em.

Ed
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Old Tuesday 5th September 2017, 06:25   #13
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Hi,

the difference between field curvature (fuzzy edge can be focused away) and other aberrations (here called astigmatism) has been properly described.
If a fuzzy edge cannot be focused away, one possible culprit is astigmatism of the binoculars. But it could also be coma, some higher order aberrations or even astigmatism of the observers eyes (although in this case the effect should be visible in other bins or telescopes with the same exit pupil at night under the stars - during daylight the smaller pupil of the eye might hide the effect).

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Old Tuesday 5th September 2017, 16:58   #14
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... 'natural' field curvature still allows peripheral objects to appear in focus, though obviously not all on the same (flat) object plane. In my opinion, this creates the best conditions for an ideal immersive view hallmarked by perceptual 'presence.'... ...Flat field binoculars induce what I can only describe as very distracting 'cardboard' image perceptions...
I know what you mean about the potential utility of the fortuitous match of field curvature to the view. It works particularly well with big vistas over vast prairies, mudflats, or water, where little but sky or clouds are visible above the horizon (and thus the poor focus of the view above a vertically centered horizon does not call attention to itself). However, in practice, while birding (critical fine detail viewing), I must say that I don't find touching up the off-axis focus of the EL SV any more necessary or laborious than I do with curve-field bins under such circumstances, and in most other viewing situations, I find that the flat field bins require much less fiddling and provide a more relaxing view to me than does a curved field.

Perhaps what you describe is another reason why I prefer curved fields without astigmatism to bins like the Zeiss FL/HT (and e.g. B&L Elite waterproof) with their very flat field (cardboard?) views blurred by astigmatism. At least with the EL SV one gets a cardboard view that is sharp! (a good quality for a bird ID tool :)

--AP
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Old Tuesday 5th September 2017, 23:20   #15
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Sorry, I've been a bit under the weather lately, so I haven't felt like contributing here. Tomorrow I'll try to post some grid pattern photos, which (to make a long story short) will support most of what Alex has been saying.

Henry

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Old Wednesday 6th September 2017, 04:06   #16
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I guess it shouldn't be too surprising that one's instrument preferences are mated to one's viewing style. In this instance I'm the logical opposite, because my head/body quickly follow my eyes in such a way that the edges rarely come into view. Thus centered, I expect the periphery to approximate my unaided, i.e., natural, visual field curvature, rather than be artificially flattened, as with an SE or SV.

Certainly astigmatism never helped anyone, but 'natural' field curvature still allows peripheral objects to appear in focus, though obviously not all on the same (flat) object plane. In my opinion, this creates the best conditions for an ideal immersive view hallmarked by perceptual 'presence.' Fortunately, the 804 Audubon, Swaro SLC-HD, and Leica BR have minimal astigmatism and well-corrected field curvature, making them very easy viewing in the field. Flat field binoculars induce what I can only describe as very distracting 'cardboard' image perceptions.

There's no right or wrong, it's all in how one prefers to use 'em.

Ed
Ed, this is an interesting post which pretty much reflects my own experiences and preferences. I've posted previously about witnessing what I've called 'ultra high definition billboard' type images through flat field binoculars such as the excellent Swarovision and SF. While a technical marvel, I don't personally find these images to be adequately engaging or immersive. I have found other Binoculars which do offer a far more immersive view. I agree there is no right or wrong, and it's great that options are available for our various preferences.

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Old Wednesday 6th September 2017, 04:54   #17
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The 8x42 HT has notable astigmatism as one approaches the edges, but I don't find it to be any more severe than plenty of other fine binoculars such as the 8x30 EII. In practice, it does not bother me at all, although I will admit that the view through a swarovision or any other binocular with similarly well-corrected edges can be addictive.
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Old Sunday 17th September 2017, 05:15   #18
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In my background of instruments used for astronomy, astigmatism is the inability to focus two different axis in the same plane. Testing a telescopic system is easy: point it at a medium-bright star at high power and rack it slowly back and forth across the focal plane. With no astigmatism the out-of-focus star will remain perfectly round on both sides of focus even when only very slightly out of focus. With astigmatism the star will go oblong on one side of focus and oblong again in another direction (usually 90 degrees from the first) on the other side of focus. Be wary though as most people have at least some astigmatism and it too will be revealed by the test. The solution is to rotate one's eye in relation to the scope. If the abberation moves with the viewer's head, then the abberation is with the viewer. If not, it is with the scope. Also be sure to let the optics completely come to temperature equilibrium before testing. How all of this applies to binocular optics is something that I'm not as familiar with and will leave to others. I hope this helps.
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