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Author Topic: Shorten the flange distance, then tilt micro-lens? why not just keep it longer  (Read 4518 times)
EinstStein
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« on: November 01, 2013, 10:17:06 PM »
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All mirror-less cameras suffer the short/tilted ray problem, from Leica M, M43, X, Nex, and now A7X. Leica deals it with the tilted micro-lens, now rumor is, A7x is following the same trick. It's much less a problem if simply keeping a longer flange distance. For DSLR, it's given.

I compared Zeiss G series lenses vs. its SLR (Contax Zeiss) series. The G series of similar focal length, such as 35-70mm or 28mm prime, is not as good as the SLR series although it's much lighter and cute. So I concluded size does matter, and the bigger size the easier to achieve better IQ.
Leica M has the need to reduce the lens size mainly due to the range finder-blockage. It's a necessary trouble and also its uniqueness.
 
It's understandable that Leica M, an century old legend, has that need. But why A7x follow that is a stupid mystery to me.
What's the point? why not just give it enough flanger distance. Simply because it's a mirror-less does not require a troublesome flange distance. For the perception of size?   Any image quality advantage over a DSLR?




 
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ErikKaffehr
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« Reply #1 on: November 01, 2013, 11:21:53 PM »
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Hi,

The flange distance does not matter, what matters is the ray angle. So a short flange distance doesn't play a role, but it makes it possible to use adapters.

SLR lenses wide angles are telecentric designs, because they need to leave room for the mirror box. So it is never a problem to mount an SLR lens on any camera. In general, symmetric lens designs are easier to make than retrofocus designs. So rangefinder cameras used symmetric designs.

The problem with short flange distance occurs when you put a rangefinder lens on a DSLR. Had the camera long flange distance, this would not be a problem.

Best regards
Erik




All mirror-less cameras suffer the short/tilted ray problem, from Leica M, M43, X, Nex, and now A7X. Leica deals it with the tilted micro-lens, now rumor is, A7x is following the same trick. It's much less a problem if simply keeping a longer flange distance. For DSLR, it's given.

I compared Zeiss G series lenses vs. its SLR (Contax Zeiss) series. The G series of similar focal length, such as 35-70mm or 28mm prime, is not as good as the SLR series although it's much lighter and cute. So I concluded size does matter, and the bigger size the easier to achieve better IQ.
Leica M has the need to reduce the lens size mainly due to the range finder-blockage. It's a necessary trouble and also its uniqueness.
 
It's understandable that Leica M, an century old legend, has that need. But why A7x follow that is a stupid mystery to me.
What's the point? why not just give it enough flanger distance. Simply because it's a mirror-less does not require a troublesome flange distance. For the perception of size?   Any image quality advantage over a DSLR?




 
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EinstStein
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« Reply #2 on: November 02, 2013, 12:02:58 PM »
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Due to the closer distance to the sensor, mirrorless camera lenses have much more sever ray angle problem than DSLR. The corner light falloff and color shading is much worse. Leica has to put in tilted microlens to compensate. In this area, DSLR has a much easy life.
While mirror less offers smaller camera body, at least thinner, I can see hardly to justify the IQ degradation. Even tilted microlens reduced somewhat the problem.

Leica M has no choice, it has a tradition and reputation to keep, but it seems odd a new system like A7x .

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uaiomex
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« Reply #3 on: November 02, 2013, 11:04:34 PM »
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Let's not forget that short lens-flange distance to film-plane helps shrink lens size, especially wide-angles. Well, at least in theory. Or how could I explain why M lenses are considerably smaller than all their slr lenses counterparts? Lack of AF and IS helps of course, but does it fully answer the question?
Eduardo

Due to the closer distance to the sensor, mirrorless camera lenses have much more sever ray angle problem than DSLR. The corner light falloff and color shading is much worse. Leica has to put in tilted microlens to compensate. In this area, DSLR has a much easy life.
While mirror less offers smaller camera body, at least thinner, I can see hardly to justify the IQ degradation. Even tilted microlens reduced somewhat the problem.

Leica M has no choice, it has a tradition and reputation to keep, but it seems odd a new system like A7x .


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Jim Kasson
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« Reply #4 on: November 02, 2013, 11:08:10 PM »
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Due to the closer distance to the sensor, mirrorless camera lenses have much more sever[e] ray angle problem than DSLR[s do]. The corner light falloff and color shading is much worse...it seems odd [in] a new system like A7x .

I think Erik pretty much nailed this one, but it doesn't sound like you're buying his reasoning. Let me take a crack at it and see if that helps.

A short flange distance allows the use of lenses with exit pupils close to the focal plane, but doesn't require them. Any lens design that will work on a camera with a long flange distance will work on one with a short flange distance, if vignetting by the mount doesn't come into play. The converse is not true: some lens designs that will work with a short flange distance won't work with a long flange distance, at least not without extending part of the lens behind the flange.

The situation is more cut and dried when you consider the use of existing lenses via adapters. The adapter cannot in general allow the rear flange of the lens to be closer to the focal plane than the front flange of the camera. Therefore, lenses from cameras with long flange distances can be mounted on cameras with short flange distances, but lenses from cameras with short flange distances cannot be mounted on cameras with long flange distances.

Therefore, cameras with short flange distances enjoy the best of both worlds. They allow the user to have maximum freedom in choosing existing lenses, while they allow lens designers designing new lenses for that mount to have maximum flexibility with the design of new lenses.

So what's not to like?

Note that this was a choice unavailable to SLR designers, since the mirror box made short flange distances impractical.

Does that make sense?

Jim
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EinstStein
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« Reply #5 on: November 03, 2013, 10:43:26 AM »
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Maybe the flange distance is too much of engineering. The whole point is the angle of the outer edge to the outer edge of the sensor in the extreme opposite direction.
When a lens has shorter distance between its rear element to the sensor, either it has to reduce the diameter of the rare element or to suffer more ray angle problem.  Reducing diameter of rare element also implies some lens quality.

There is No magic.
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BJL
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« Reply #6 on: November 03, 2013, 01:31:47 PM »
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A short flange distance allows the use of lenses with exit pupils close to the focal plane, but doesn't require them. Any lens design that will work on a camera with a long flange distance will work on one with a short flange distance, if vignetting by the mount doesn't come into play. The converse is not true: some lens designs that will work with a short flange distance won't work with a long flange distance, at least not without extending part of the lens behind the flange.
Agreed, and let me add two points about a shorter flange distance:

1) It not only allows using any lens design that works on a SLR (such as with adaptors); it also allows lens designs that take advantage of the option of having rear elements closer to the focal plane while still having high exit pupil and so near-telecentric behavior, not needing fancy off-set micro-lenses. In fact, such lens designs are sometimes used in fixed-lens digital cameras, for compactness.

2) On the other hand, it also allows the option to reduce lens size and weight in ways that compromise optical quality and/or add the need for off-set micro-lenses. It seems likely that this option is taken at least for some of the smaller and less expensive lenses for non-SLR cameras. But some lenses taking that option does not mean that there are not also options for high quality lens designs. As a recent example, the new Olympus 12-40/2.8 has got good reviews for optical quality; contrast this to the distinctly less optically excellent Olympus 12-50/3.5-6.3, which also serves well, but for a quite different balance of size/price/performance. On my E-M5, I swap between that 12-50 and the far bulkier adaptor-mounted Olympus 12-60/2.8-4 SLR lens, according to my priorities for a particular outing.


Choice is good.
« Last Edit: November 03, 2013, 01:35:08 PM by BJL » Logged
EinstStein
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« Reply #7 on: November 03, 2013, 02:57:36 PM »
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When the shorter flange distance requires to tilt the microlens, it is too short, and the image quality suffers.
It is understandable if it is for backward compatibility, like Leica M, but it is stupid for a new system.
Is it Sony intention to piggyback on Leica M lens as the core value?
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ErikKaffehr
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« Reply #8 on: November 03, 2013, 02:58:46 PM »
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Hi,

You seem to be obsessed with flange distance. Let's assume you want to put an EOS lens on a Sony A7. You need an extension tube of 44-18 = 26 mm. Problem solved. You don't need to have any part of the optical group at flange distance, but a shorter flange distance gives you more options.

Best regards
Erik

Maybe the flange distance is too much of engineering. The whole point is the angle of the outer edge to the outer edge of the sensor in the extreme opposite direction.
When a lens has shorter distance between its rear element to the sensor, either it has to reduce the diameter of the rare element or to suffer more ray angle problem.  Reducing diameter of rare element also implies some lens quality.

There is No magic.
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EinstStein
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« Reply #9 on: November 03, 2013, 03:19:08 PM »
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Why do you want to put Canon's lens on Sony's camera? Sony's lens not good enough?

Let's say your really want foreign lenses on Sony's camera, you'll find A7 works better than A7R, if it's true that A7 does not have A7R's tilted micro-lens. You'll find A7R's micro-lens suffers over-compensation on the ray angle problem.
Sony has to work very hard on every new lens to make sure the A7R's tilted micro-lens does not fall into the same pitfall, and this is almost unsolvable problem for tele-lens.
In the end you'll need both A7 and A7R: A7 for the lenses that do not need ray angle compensation, and A7R for the lens of dedicated designed.
But you'll upset why not just stay with Canon.

Sony, on the other hand, will design all new bodies without tilted micro-lenses and design all new lenses with long flange distance to correct its mistake.
The good new is, you are all correct, the lenses with longer flange distance are easier to adapt by simply adding a spacer.

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BJL
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« Reply #10 on: November 03, 2013, 04:06:43 PM »
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Why do you want to put Canon's lens on Sony's camera? Sony's lens not good enough?

Let's say your really want foreign lenses on Sony's camera, you'll find A7 works better than A7R, if it's true that A7 does not have A7R's tilted micro-lens.

You'll find A7R's micro-lens suffers over-compensation on the ray angle problem.
To your question, the answer that everyone is giving you is that an extra option like more lens choices is never bad. In this case, maybe someone already owns some good Canon lenses, or the larger Canon lens range has some options not offered by Sony.

To your comment about microlenses making things worse for longer focal lengths by over-compensating: do you have any evidence for that claim?
The analysis that I read a few years ago by an optical designer (Joe Wisniewski?) was that the offset angle needed is too small to cause any problems with longer lenses. About 7 degrees for the offset lenses used by Leica, IIRC.
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EinstStein
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« Reply #11 on: November 03, 2013, 06:08:33 PM »
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The Amount of overcompensation can be easily calculated. If the tilted microlens has 2 stops optical based compensation, then the telelens that supposed to be fine without tilted microlens will suffer 2stops overcompensation. Here I did Not count the software based compensation because that factor can be undo easily.
The more trouble might  be with the color shading and sharpening.
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EinstStein
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« Reply #12 on: November 03, 2013, 06:27:23 PM »
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The advantage of using foreign lenses is just a fantasy. I have done that a lot before, including putting hasselblad on Canon, and Leica/Zeiss on Next and m43. They simply never justify to switch the system.

But that is not my main point. Based on a simple engineering judgement, tilting the microlens with a Shortened fange distance is a clever bug fix. But building a new system then tilting the microlens is rediculous. For its native system, it has an inferior starting point witn respect to the system build for its own, not counting to piggyback on any foreign lenses.
« Last Edit: November 03, 2013, 06:29:15 PM by EinstStein » Logged
Glenn NK
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« Reply #13 on: November 03, 2013, 07:11:21 PM »
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Why do you want to put Canon's lens on Sony's camera? Sony's lens not good enough?


1)  Because Canon has a wide range of very good lenses (who makes the best TS lens?).

2)  Because Sony doesn't have many lenses.

3)  It will take quite a while for Sony to catch up with lenses (maybe they'll get Canon to make lenses for them and Canon will get to use Sony sensors  Cool.
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BJL
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« Reply #14 on: November 03, 2013, 08:38:11 PM »
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The Amount of overcompensation can be easily calculated. If the tilted microlens has 2 stops optical based compensation, then the telelens that supposed to be fine without tilted microlens will suffer 2stops overcompensation.
That is total nonsense. Off-set microlens compensation is about angles of incidence of the incoming light to the sensor, and so angling each microlens towards the center of the lens by an angle that is proportional to how far it is from the center. You cannot possibly measure the angles needed and the effect of those angles on lenses with higher exit pupil from some measure of the amount of corner vignetting, which anyway is different for each lens. For one thing you need to know the acceptance angle of the microlenses ...
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EinstStein
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« Reply #15 on: November 03, 2013, 09:21:55 PM »
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That is total nonsense. Off-set microlens compensation is about angles of incidence of the incoming light to the sensor, and so angling each microlens towards the center of the lens by an angle that is proportional to how far it is from the center. You cannot possibly measure the angles needed and the effect of those angles on lenses with higher exit pupil from some measure of the amount of corner vignetting, which anyway is different for each lens. For one thing you need to know the acceptance angle of the microlenses ...

If you can't face the truth, so be it!
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xpatUSA
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« Reply #16 on: November 05, 2013, 09:44:33 PM »
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If you can't face the truth, so be it!

Hopefully the end of this inane thread. Let it be so!
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best regards,

Ted
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« Reply #17 on: November 06, 2013, 06:59:40 AM »
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Glen,

Quote
1)  Because Canon has a wide range of very good lenses (who makes the best TS lens?).

2)  Because Sony doesn't have many lenses.

3)  It will take quite a while for Sony to catch up with lenses (maybe they'll get Canon to make lenses for them and Canon will get to use Sony sensors  Cool.

1. Use a Canon body.

2. Use a Canon body.

3. Use a Canon body.

Job done. Wink
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Vladimirovich
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« Reply #18 on: November 06, 2013, 09:17:56 AM »
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Glen,

1. Use a Canon body.

2. Use a Canon body.

3. Use a Canon body.

Job done. Wink

somebody probably wants to have FF, 36mp, high DR @ base ISO camera for his landscape shot with T/S lenses...  and Canon does not deliver (yet) the camera, but does offer a good lens... and no - I do not want to spend time with PhotoAcute for superresolution/DR out of several Canon raws, sorry
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Glenn NK
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« Reply #19 on: November 07, 2013, 03:11:36 PM »
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somebody probably wants to have FF, 36mp, high DR @ base ISO camera for his landscape shot with T/S lenses...  and Canon does not deliver (yet) the camera, but does offer a good lens... and no - I do not want to spend time with PhotoAcute for superresolution/DR out of several Canon raws, sorry

I'm familiar with a "pretty good" photog that stitches with his D800E body:

http://www.naturescapes.net/forums/viewtopic.php?f=4&t=238262

(three vertical frames with a 28 mm + D800E).
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