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Flat Field technology: the hows, the why's, the consequences (2 Viewers)
- Thread starter Renze de Vries
- Start date
The Nagler and Panoptic telescope eyepieces offer proof that sharp edge and pincushion can coexist. Also they weigh about as much as a binocular.
Ironically, pincushion is undesirable in an astronomical telescope, where the view is almost certain to be static and star arrangement is an important thing to be preserved if possible.
Things are tough all over huh?
Ron
Ironically, pincushion is undesirable in an astronomical telescope, where the view is almost certain to be static and star arrangement is an important thing to be preserved if possible.
Things are tough all over huh?
Ron
It all seems quite relative to me.
There were apochromats long before the ED psuedo-apochromats.
Nagler EPs predate all this history being fussed over, and they are far flatter and wider than
the so-called "flat-field" technology, which is one or two aspheric lenses in a sexy marketing dress.
You gotta hand it to Nikon, though: the whole Japanese optical industry was swept by
the Asahi "amber" coatings at the same time (same Asahi/Zeiss project and patents) but lost the
marketing/sexiness boat to the Germans. Zeiss actually imported Asahi-coated lenses for a while.
But....Nikon wowed the crowd by putting aspherics into binoculars, which actually save money
over adding a bunch more meniscus elements, and calling it 'field flattening'. It does a lot if you
already have many elements. It does just a little better with EPs in the Aculon line with fewer elements.
Someday I hope to figure out how to demonstrate some of the oldies I have
were done with a parabolic grind. They do have the best resolution I've seen.
There were apochromats long before the ED psuedo-apochromats.
Nagler EPs predate all this history being fussed over, and they are far flatter and wider than
the so-called "flat-field" technology, which is one or two aspheric lenses in a sexy marketing dress.
You gotta hand it to Nikon, though: the whole Japanese optical industry was swept by
the Asahi "amber" coatings at the same time (same Asahi/Zeiss project and patents) but lost the
marketing/sexiness boat to the Germans. Zeiss actually imported Asahi-coated lenses for a while.
But....Nikon wowed the crowd by putting aspherics into binoculars, which actually save money
over adding a bunch more meniscus elements, and calling it 'field flattening'. It does a lot if you
already have many elements. It does just a little better with EPs in the Aculon line with fewer elements.
Someday I hope to figure out how to demonstrate some of the oldies I have
were done with a parabolic grind. They do have the best resolution I've seen.
elkcub
Silicon Valley, California
henry link
Well-known member
Thought I mention that the SV corrects field curvature and astigmatism for central vision. When the eye's central vision is swiveled toward the field edge the image remains sharp. It's hard to judge what happens for peripheral vision since that's inherently so poor.
Also, remember that an unrelated and for some uncomfortable "mustache" distortion is occurring simultaneously with the correction of field curvature in the SV field. As Ron mentioned in post #22 field curvature can be corrected with any amount of pincushion.
Also, remember that an unrelated and for some uncomfortable "mustache" distortion is occurring simultaneously with the correction of field curvature in the SV field. As Ron mentioned in post #22 field curvature can be corrected with any amount of pincushion.
Field curvature and rolling ball are interesting in that opinions vary so widely on them. I did Holger's k-test, and was most closely in his group B, which was seemingly one of the most normal ways of reacting to AMD and RB.
I see some rolling ball in my Nikon 10x42 SE, but it does not bother me. I see virtually no RB in my 10x42 Canon, but that may be partly due to having used it so much over the last 7-8 years. But when I deliberately try to see angular magnification distortion in it (radial dimensions collapsing towards the very edge of the field) I can see very moderate amounts but not much by any means. A week ago I had the Zeiss SF 8x42 and a brand new Swaro SV 8.5x42 for testing for a few days, and spent a fair amount of time visually evaluating their viewing properties. Now, contrary to what the graph on Holger's webpages would suggest, where the SF should be more or less at the sweet spot for distortion and AMD, to my eyes it had significantly more RB and more pronounced AMD than the SV, which had a little more than the Canon. I would judge that the SV would be for me easy to get accustomed to, the Zeiss more difficult but very likely possible. The reason why I find the Zeiss acceptable in use despite relatively high AMD is that the field of view is very wide and the effects of AMD are only visible in the last 10-15% of the field off axis. Now, in normal viewing and panning I tend to have my eyes more or less viewing along the central third or so of the view field. Thus the potentially objectionable stuff happens in the peripheral vision area and is hardly a problem.
One interesting thought came to me when thinking about flat field technology and the design compromises involved. This comes from looking at the cutaway views of the eyepieces of the Canon 10x42 and the SF, as well as inspecting the eyepiece of the SV with the eyecup removed. What I mean that in the Canon design, the 23mm wide eye lens is not the largest diameter lens in the system by a long shot. The third lens in is much wider, and the twist-out eyecup diameter is 44mm. In the SF (25mm eye lens, 39mm eyecup diameter) and SV (24mm eye lens, 40mm eyecup diameter) the eye lens is about as wide as it can be given the overall external diameter of the eyepiece inside the extendable and removable eyecup cylinder.
It may be that the edge distortion characteristics in the SF, and to a lesser degree in the SV, are at least partially what they are in order to allow for an eyepiece that fits within certain physical dimensions while providing a wide enough true field. Hopefully the dismal Canon eyecups could be designed slimmer by some clever engineering, but partly they seem to so huge in order to accommodate that large third lens.
Kimmo
I see some rolling ball in my Nikon 10x42 SE, but it does not bother me. I see virtually no RB in my 10x42 Canon, but that may be partly due to having used it so much over the last 7-8 years. But when I deliberately try to see angular magnification distortion in it (radial dimensions collapsing towards the very edge of the field) I can see very moderate amounts but not much by any means. A week ago I had the Zeiss SF 8x42 and a brand new Swaro SV 8.5x42 for testing for a few days, and spent a fair amount of time visually evaluating their viewing properties. Now, contrary to what the graph on Holger's webpages would suggest, where the SF should be more or less at the sweet spot for distortion and AMD, to my eyes it had significantly more RB and more pronounced AMD than the SV, which had a little more than the Canon. I would judge that the SV would be for me easy to get accustomed to, the Zeiss more difficult but very likely possible. The reason why I find the Zeiss acceptable in use despite relatively high AMD is that the field of view is very wide and the effects of AMD are only visible in the last 10-15% of the field off axis. Now, in normal viewing and panning I tend to have my eyes more or less viewing along the central third or so of the view field. Thus the potentially objectionable stuff happens in the peripheral vision area and is hardly a problem.
One interesting thought came to me when thinking about flat field technology and the design compromises involved. This comes from looking at the cutaway views of the eyepieces of the Canon 10x42 and the SF, as well as inspecting the eyepiece of the SV with the eyecup removed. What I mean that in the Canon design, the 23mm wide eye lens is not the largest diameter lens in the system by a long shot. The third lens in is much wider, and the twist-out eyecup diameter is 44mm. In the SF (25mm eye lens, 39mm eyecup diameter) and SV (24mm eye lens, 40mm eyecup diameter) the eye lens is about as wide as it can be given the overall external diameter of the eyepiece inside the extendable and removable eyecup cylinder.
It may be that the edge distortion characteristics in the SF, and to a lesser degree in the SV, are at least partially what they are in order to allow for an eyepiece that fits within certain physical dimensions while providing a wide enough true field. Hopefully the dismal Canon eyecups could be designed slimmer by some clever engineering, but partly they seem to so huge in order to accommodate that large third lens.
Kimmo
elkcub
Silicon Valley, California
This is partly what leads me to hypothesize that flat field technology attempts to fit the system's Petzval curvature to the retinal surface.
If the main idea is to allow the eye to rotate to see the field edge clearly, would that not be accomplished best by matching the system's Petzval curvature to the retina's? Then, when the eye rotates the field edge would position over the eye's central angle of vision while still being in focus. I guess an optimized system would include modeling the user's eye dynamics, which includes rotation geometry, pupil clipping, and so forth. Tradeoffs would be involved. And it would also tend to optimize peripheral vision for the purposes nature intended: object and motion detection.
I realize this is very oversimplified. For one thing, the eye's center of rotation is anterior to it's geometric center, and other constraints enter the picture, such as ray clipping by the pupil, and instinctive repositioning at the eyepiece.
This, however, is my current understanding as to how the thing work. I can also envision a wide range of implementation differences between manufacturers, resulting in a confusing array of preferences and perceptual adaptation opportunities in the user population. (Heads up, Pileatus !)
Your thoughts ... or anyone else's?
Ed
PS. Incidentally, I would be a bit cautious about drawing strong conclusions from camera images in this area, because cameras are designed with flat film planes in mind — so it could be misleading. Here, we are talking about projecting into basically spherical caps.
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elkcub
Silicon Valley, California
Yeah. :t:
For an uncoupled system, like a TV screen, distance changes with eye/head rotation angle, so a curved screen tends to overcome the effect. Same general idea.
Ed
NDhunter
Experienced observer
Kimmo:
You are one of those around the forum, that have had some time to compare the SV and SF it
seems.
As you have read, many are wondering about performance of the new SF, as some contrary observations
have been mentioned in several ways.
Have you spent time with any resolution testing, and comparisons that would be useful to us?
Your articles in Alula Magazine were very well done, and I have gone back and found those for a review of
some older optics. Are you doing any other reviews like that we can find now on the net?
Edit to Add:
Your mention of AMD in these 2 binoculars is interesting, as Zeiss told us they had that all figured out. I have had several years of experience with the SE's, the EDG and the Swarovision
and I have not ever seen any AMD. I am one that does not know what it is.
How does the EDG compare in your testing ? I find this binocular a very good compromise
all the way around.
Jerry
You are one of those around the forum, that have had some time to compare the SV and SF it
seems.
As you have read, many are wondering about performance of the new SF, as some contrary observations
have been mentioned in several ways.
Have you spent time with any resolution testing, and comparisons that would be useful to us?
Your articles in Alula Magazine were very well done, and I have gone back and found those for a review of
some older optics. Are you doing any other reviews like that we can find now on the net?
Edit to Add:
Your mention of AMD in these 2 binoculars is interesting, as Zeiss told us they had that all figured out. I have had several years of experience with the SE's, the EDG and the Swarovision
and I have not ever seen any AMD. I am one that does not know what it is.
How does the EDG compare in your testing ? I find this binocular a very good compromise
all the way around.
Jerry
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Alexis Powell
Natural history enthusiast
You're right that Nikon was first to put flat-field technology in a birding bin, but it started way before 1995. Nikon used it in their first premium birding roof, the Nikon 8x40 Classic Eagle which was released in the mid 1980s. Both Fujinon and Nikon have long used it in their best porros (e.g. Nikon 7x50 ProStar).
--AP
WJC
Well-known member
Hi Jerry:
I don't doubt the 10x42 SE arrived in 1995--wow! What a bino! However, the FMT-SX arrived long before that, the Nikon Prostar arrived before that, and Zeiss probably had a flat-field design before that.
No big deal was made of it because they weren't trying to please a bunch of guys on a binocular forum; they were just trying to make a better bino. They weren't dealing with a flat field technology that didn't exist.
Bill
In the big picture, consumer binoculars are not the source of most technology.
Correctors to flatten the field phase response predate all that timeline,
and are very similar in action (but for a more severe problem).
The Schmidt corrector plate (what they called a flattener back then)
for reflecting telescopes appeared in 1931. Flattening the field in microscopes
also predates binocular use.
Multi-coating appeared in binoculars about 1943, but was a US military secret at the time.
The patent was 1948, I think. You can see it on many old US Navy 7x50s.
Correctors to flatten the field phase response predate all that timeline,
and are very similar in action (but for a more severe problem).
The Schmidt corrector plate (what they called a flattener back then)
for reflecting telescopes appeared in 1931. Flattening the field in microscopes
also predates binocular use.
Multi-coating appeared in binoculars about 1943, but was a US military secret at the time.
The patent was 1948, I think. You can see it on many old US Navy 7x50s.
henry link
Well-known member
I just noticed this two year old thread, which covers some of the same ground.
http://www.birdforum.net/showthread.php?t=252903
http://www.birdforum.net/showthread.php?t=252903
Alexis Powell
Natural history enthusiast
Although I offered a correction to NDHunter/Jerry's post, I still agreed with his main point, which has been lost in this discussion of when flat-field technology was invented. Nikon was the first to put it in a birding binocular, and thank goodness they did. The Nikon 8x40 Classic Eagle was my first top-end binocular. I tried the Leica and Zeiss competition of the time, and I didn't have any special names for what I was seeing, but I found their fuzzy view off-axis impossible to ignore and very disturbing. Given the reputations of the German brands, I couldn't understand why their birding roofs were only sharp right in the middle of the view (just like my Bushnell porros, except with inferior contrast!). When Zeiss introduced phase correction, the superior contrast of the 7x42 BGATP over the Classic Eagle was obvious, and the Zeiss 7x42 was also quite a bit brighter (with its AK prisms) and had a wider field of view, so it became my new birding bin. Still, I really missed the full-field "sweet spot" of the Nikon. It took almost 10 years for Nikon to introduce a phase-corrected successor to the Classic Eagle (the Venturer LX/HG), about 25 years to see flat-field tech in a euro-alpha birding roof (the SV), and an excruciating really long (nearly 30 year) wait to see, in the SF, my favorite qualities of the Nikon Classic Eagle merged with my favorite qualities of the Zeiss 7x42 BGATP. Thank goodness Swarovski took the plunge or else we might still be waiting for Zeiss. All that waiting has done nothing to convince me that the euro-alpha brands have been fully committed to the task of "just trying to make a better bino", at least for birding, or at least until now. But we still haven't seen flat-field from Leica, and we still haven't seen any of these makers of supposedly no-compromise bins use variable-ratio focus, which would greatly improve the performance of close-focusing bins. So I'm not convinced we should be waiting around quietly for them to make improvements/changes as they see fit. As a consumer, I will continue to be a squeaky wheel, in the tradition of Better View Desired and now Birdforum (minus the fanboys).
--AP
P.S. When I wrote the above, I was thinking based on faulty recollection that the Classic Eagle was introduced in 1986. Actually, it was released in 1984. So my wait times for Zeiss and Swarovski to catch up were underestimates by about 8%.
--AP
P.S. When I wrote the above, I was thinking based on faulty recollection that the Classic Eagle was introduced in 1986. Actually, it was released in 1984. So my wait times for Zeiss and Swarovski to catch up were underestimates by about 8%.
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henry link
Well-known member
Alexis Powell
Natural history enthusiast
Oh yes. A version of it was featured in the Nikon sport optics brochure (which I still have) that made me aware of the Classic Eagle in the first place. I spent a lot of time ogling that diagram and looking over the specs before I was able to save enough money to buy them ($500 at the time, and I was a teenager). I was almost afraid to touch them at first, they seemed so intricate, with all their precisely-joined metal parts, joined by screws or threading, but they are reassuringly very solid. They were miraculous for birding in several ways that I hadn't previously experienced, including having enough eye-relief to use with glasses, and having focus that didn't stiffen in the cold. Biggest faults were poor transmission, lack of phase correction (not a fault compared to other roofs when they were first released), and poor "hang". Note the lack of true internal focusing (the objectives move behind the waterproofing window). I still have them, along with a spare set of eyecups, and take them out birding occasionally for old time's sake.
--AP
PS -- To anyone interested in the Classic Eagle, it really is a fascinating binocular. Have a look at it, and compare the specs to other roofs of the time and it is clear that it was Nikon's attempt to make the finest birding/nature roof-prism binocular of the day (1984). It was a one-off design (no 10x or x32 equivalents) unlike any of Nikon's other bins before or since except a few styling similarities (e.g. of the focus knob) to the also unique 9x30 and 12x36 DCF Execulite models.
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NDhunter
Experienced observer
Alexis:
I suppose we all have a wish list, and I have seen you wanting some
makers to offer a variable ratio focuser.
I feel that is a complex requirement that I or most do not have a need
or want for. Keep things dependable and reliable.
Swarovski, if you are watching, I would not put this anywhere near the
list of things to do.
Alexis, the Brunton Epoch is now on a clearance sale and this model has a variable ratio focuser.
Discontinued and gone.
So there is your wish. :smoke:
Jerry
Steve C
Well-known member
Jerry,
You really ought to make some effort to set aside your biases and really look at an Epoch
. Yes they are discontinued and gone, but they are a very good binocular. They were pretty optimistically priced, if I recall they were always listed as just about the most expensive glass on the market. However, that variable rate focus is likely the best focus system ever put on a binocular. So at these prices, if a variable ratio focus is on anybody's wish list, this is a good chance to get one. For now the only chance. Swarovski or anybody else would be wise to look more closely at it. There is likely some patent issues securing it to Brunton.
