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Equipment & Techniques => Digital Cameras & Shooting Techniques => Topic started by: EinstStein on November 01, 2013, 11:17:06 PM

Title: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: EinstStein on November 01, 2013, 11:17:06 PM
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?




 
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: ErikKaffehr on November 02, 2013, 12:21:53 AM
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?




 
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: EinstStein on November 02, 2013, 01:02:58 PM
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 .

Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: uaiomex on November 03, 2013, 12:04:34 AM
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 .


Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: Jim Kasson on November 03, 2013, 12:08:10 AM
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
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: EinstStein on November 03, 2013, 11:43:26 AM
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.
Title: shorter flange only adds options; some sacrifice quality for size, but not all
Post by: BJL on November 03, 2013, 02:31:47 PM
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.
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: EinstStein on November 03, 2013, 03:57:36 PM
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?
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: ErikKaffehr on November 03, 2013, 03:58:46 PM
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.
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: EinstStein on November 03, 2013, 04:19:08 PM
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.

Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: BJL on November 03, 2013, 05:06:43 PM
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.
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: EinstStein on November 03, 2013, 07:08:33 PM
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.
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: EinstStein on November 03, 2013, 07:27:23 PM
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.
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: Glenn NK on November 03, 2013, 08:11:21 PM
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  8).
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: BJL on November 03, 2013, 09:38:11 PM
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 ...
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: EinstStein on November 03, 2013, 10:21:55 PM
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!
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: xpatUSA on November 05, 2013, 10:44:33 PM
If you can't face the truth, so be it!

Hopefully the end of this inane thread. Let it be so!
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: AreBee on November 06, 2013, 07:59:40 AM
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  8).

1. Use a Canon body.

2. Use a Canon body.

3. Use a Canon body.

Job done. ;)
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: Vladimirovich on November 06, 2013, 10:17:56 AM
Glen,

1. Use a Canon body.

2. Use a Canon body.

3. Use a Canon body.

Job done. ;)

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
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: Glenn NK on November 07, 2013, 04:11:36 PM
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).
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: scooby70 on November 11, 2013, 09:40:23 AM
Glen,

1. Use a Canon body.

2. Use a Canon body.

3. Use a Canon body.

Job done. ;)

There's also the issue of bulk and weight.

I have a 5D which I hardly ever use as I prefer using a CSC. The Sony A7 I've ordered will give me better ultimate IQ than I get from both my current CSC and 5D in a much more compact and lighter body and lens combo than my Canon gear.
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: ErikKaffehr on November 11, 2013, 03:02:08 PM
I found out that the Alpha 99 I have also has offset micro lenses. I guess hat may help a bit with large aperture lenses, too.

Best regards
Erik


There's also the issue of bulk and weight.

I have a 5D which I hardly ever use as I prefer using a CSC. The Sony A7 I've ordered will give me better ultimate IQ than I get from both my current CSC and 5D in a much more compact and lighter body and lens combo than my Canon gear.
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: Christoph C. Feldhaim on November 11, 2013, 03:15:35 PM
The main advantage of this short flange distance/exit pupil to sensor distance thing is the ability to use Biogon (symmetric) design wideangles. These lenses autocorrect due to their symmetry many aberrations (especially distortion) much better than Distagon (reverted telelens) designs.

In times of lens profile based autocorrection of Vignette, CA, distortion and purple fringing in Raw developers it can be argued if this design is still direly needed, the opposite is true: symmetric short focal length designs cause a whole lot of problems on digital sensors. Some lens / Digiback combos simply don't work because of this, even if you take correction shots for LCC profiles.

However up to the time where this technology became available short exit pupil/sensor(film) distance made a LOT of sense in terms of image quality.
Title: High exit pupil with rear elements near the sensor is also useful
Post by: BJL on November 11, 2013, 04:18:39 PM
The main advantage of this short flange distance/exit pupil to sensor distance thing is the ability to use Biogon (symmetric) design wide angles.
Those days, a low flange distance is not only for short focal length symmetric lenses: some of the best near-telecentric designs also have rear elements very close to the focal plane, despite having a high exit pupil, so they are not like the classic inverted telephoto retro-focus designs first developed for movie cameras and then for SLRs. For example, the Sony RX1 reportedly has its rear lens elements very close to the sensor, as did its ancestors from a decade ago, the Sony F707, F717 and F828; those old cameras definitely did not use offset micro-lenses.
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: hjulenissen on November 11, 2013, 04:24:51 PM
Obviously, any designated MILF lens _could_ include the equivalent of a converter bolted on. Thus, anything that is possible (optically) when you design a DSLR camera + DSLR lens, is also possible when you design a MILF camera + MILF lens. What you gain is the possibility of designing lenses that could never have been used on a DSLR due to the mirror: lenses that include optical elements very close to the sensor.

It is safe to assume that having more freedom to design something is never negative. It seems that in this case, for certain designs, it allows some features that are positive for image quality, compactness etc. But if you take advantage of those features, you also get some drawbacks.

Why is it that film could accept wide angles of incoming light while digital cannot? Is this a fundamental property of ccd/cmos sensors, or is it some trade-off (perhaps with micro-lenses/sensitivity)?

-h
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: Christoph C. Feldhaim on November 11, 2013, 04:34:05 PM
Why is it that film could accept wide angles of incoming light while digital cannot? Is this a fundamental property of ccd/cmos sensors, or is it some trade-off (perhaps with sensitivity)?



From http://www.luminous-landscape.com/tutorials/vignetting.shtml
Quote
The second issue is that the photo sites (individual pixels) on a sensor do not lay on the surface of the chip, but rather, in shallow wells. This means that the light hitting the ones toward the corners of the image area lose some photons, because these are blocked by the sides of the well. Less photons, less exposure. Less exposure of the corners vs the center = vignetting.
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: EinstStein on November 12, 2013, 11:48:22 AM
It is correct that a lens designed for a longer flange distance  can be mounted on a short flange distance body, subject to a proper mountinng adapter, if everything else is equal.
But it is no longer true if the sensor on the short flange body is not compatible. Tilted or offset  microlens can be one of the cause.
If the body need the offset microlens, the flange distance is too short. It can still be good if the lens is design to take this advantage or to tolerate this disadvantage,but it will loose image quality for the lenses that were designed for the plain straight sensor.
It can even cause trouble for the lenses designed for a offset microlens with less offset. Actually, an sensor with offset microlens can be more picky than a straight sensor.
Any compensation can have the troubles of overcompensation for ones that do not need compensation.
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: Christoph C. Feldhaim on November 12, 2013, 12:02:23 PM
Those days, a low flange distance is not only for short focal length symmetric lenses: some of the best near-telecentric designs also have rear elements very close to the focal plane, despite having a high exit pupil, so they are not like the classic inverted telephoto retro-focus designs first developed for movie cameras and then for SLRs. For example, the Sony RX1 reportedly has its rear lens elements very close to the sensor, as did its ancestors from a decade ago, the Sony F707, F717 and F828; those old cameras definitely did not use offset micro-lenses.

It is correct that a lens designed for a longer flange distance  can be mounted on a short flange distance body, subject to a proper mountinng adapter, if everything else is equal.
But it is no longer true if the sensor on the short flange body is not compatible. Tilted or offset  microlens can be one of the cause.
If the body need the offset microlens, the flange distance is too short. It can still be good if the lens is design to take this advantage or to tolerate this disadvantage,but it will loose image quality for the lenses that were designed for the plain straight sensor.
Any compensation can have the trouble of overcompensation for ones that do not need compensation.

Long story short:
Short exit pupil-sensor distance can cause much more problems on digital sensors than on film,
but still is definitely not obsolete as the example of the Sony RX 1 clearly shows.

And now for something completely different ....
http://www.youtube.com/watch?v=KDPTC-yAmgo
:D

Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: scooby70 on November 12, 2013, 07:37:56 PM
Is digital v film a fair comparison any more?

Forgive me if I'm on the wrong track but did we look at film shots so very closely? Was film flat in the camera? Is it fair to complain if something in a digital camera is 1 micron out of alignment and we can detect it when looking at 400% on screen?

I'm just asking :D
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: BJL on November 12, 2013, 08:16:17 PM
Long story short:
Short exit pupil-sensor distance can cause much more problems on digital sensors than on film,
but still is definitely not obsolete as the example of the Sony RX 1 clearly shows.
One more time: "short exit pupil" is not the same as "short back focus", which means "rear lens elements close to the focal plane". A lens design can have a reasonably high exit pupil (near-telecentric design) even though its rear-most lens element is very close to the focal plane, as illustrated by cameras like the Sony F707 from 2001, which had rear elements very close to the focal plane and no offset microlenses yet had no major problems with "microlens vignetting" because the lens design had an adequately high exit pupil.

The RX1 lens has short back-focus, but is there any evidence that it has a low exit pupil? If I am remembering correctly, the lens did not look anything like a symmetrical design in the picture I saw.
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: EinstStein on November 12, 2013, 09:09:34 PM
Short exit pupil or short back focus do not reveal the basic problem. While geometrical optics is a good approximation, a more precise view is the wave optics. The wave optics better describes the fact that the image is the Integrated result of the light from every point at the "boundary". (Huygen's theory").
Here the boundary can be seen as the rear most lens element. If the rear most element is too close to the image plain, there will be sever ray angle, measured from the outer most edge of the lens to the opposite farthest edge of the sensor. So, the ray angle problem is really the function of the distance from the dearest lens to the sensor.
A lens design can reduce the effect if the amount of light from the other edge of the lens is weighted And reduced,so that the ray angle problem is compressed,but this also means an inferior lens design. Basically it means the diameter of there rear element can be reduced because it can be seen, practically, redundant.

Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: BJL on November 12, 2013, 09:27:37 PM
If the rear most element is too close to the image plain, there will be sever ray angle, measured from the outer most edge of the lens to the opposite farthest edge of the sensor. So, the ray angle problem is really the function of the distance from the dearest lens to the sensor.
Not necessarily: you assume that some significant amount of light has to travel from one edge of the rear element to the opposite edge of the sensor, but the existence of lenses with exit pupil well inside the lens and the chief rays striking the lens nearly perpendicular despite the rear element being close to the sensor shows that this is not true. With those lenses, light exiting near one edge of the lens is going almost entirely to that side of the sensor, and not only the chief ray but the whole light cone arriving near an edge of the sensor comes from the part of the rear element near that side.

The difference between wave optics and the geometrical optics approximation is rather unimportant to this topic, and certainly is at large enough aperture sizes (small enough f-stops) where diffraction is a minor effect --- diffraction being the main manifestation of the imperfection in the geometric optics approximation. At small apertures instead, the light cone (of geometrical optics) is narrow, and close to the chief ray, and so it is even more true that the entire light cone reaching a point near the edge of the sensor comes from a part of the rear element close to the same edge.

As far as I know, geometric optics and computational ray tracing is still the way that camera lens design is done, but if you have evidence to the contrary, please let me know.

P. S. There are some useful illustrations at http://www.edmundoptics.com/technical-resources-center/imaging/telecentricity-and-telecentric-lenses-in-machine-vision/
Image space telecentricity is what matters for sensors, and figure 3 makes the situation clearest.
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: EinstStein on November 12, 2013, 10:26:29 PM
Let's see two examples.
1. imaging you are standing in front of a 4m x 4m glass window to watch a moon. I bet you can see any difference in the clarity if you cover most of the glass but leave only a peek hole of a quarter coin. You will not experience any ray angle problem.
2. Imaging again you are watching the moon through a high quality, large telescope, yo'll know every mm of the glass matters for the brightness and the image clarity. Now try to put the image on a picture.
How do you explain the difference between the example 1 and 2?
The 2nd example shows what matters for a high quality optical system and the 1st example is a low quality optical system.


Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: BartvanderWolf on November 13, 2013, 05:36:38 AM
Not necessarily: you assume that some significant amount of light has to travel from one edge of the rear element to the opposite edge of the sensor, but the existence of lenses with exit pupil well inside the lens and the chief rays striking the lens nearly perpendicular despite the rear element being close to the sensor shows that this is not true. With those lenses, light exiting near one edge of the lens is going almost entirely to that side of the sensor, and not only the chief ray but the whole light cone arriving near an edge of the sensor comes from the part of the rear element near that side.

I fully agree with that. The exit pupil is what matters, and that determines the angle of incidence of the image forming rays, and then the microlenses reduce the angle of incidence even further to almost perpendicular (to reduce mask shielding and tunneling/crossover effects). Rear element distance is not very relevant (although there may be some correlation with the lens design).

To give an idea of what we're talking about, the Exit Pupil (approx. 17mm diameter) of my TS-E 24mm is approx. 74mm away from the sensor plane, and the Exit Pupil of the TS-E 45mm (approx. 25mm diameter) is even approx. 95mm away from the sensor plane (it apprears to be near the front of the lens). These will produce image rays that are approaching perpendicular incidence, and that angle will be hardly affected by the microlenses, regardless of their offset.

The slight radial micro-lens offset towards the center of the sensor array only helps to avoid focused light hitting more than one microlens and would potentially allow a different index of refraction and/or shape of the microlens material. Because of the spherical lens shape, the micro-lenses will redirect/condense the light coming from a variety of angles just fine, all becoming more perpendicular.

Cheers,
Bart
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: BartvanderWolf on November 13, 2013, 05:40:32 AM
How do you explain the difference between the example 1 and 2?

Micro-lenses are not an optical image forming device, they are condensers that change the angle of already focused incident light to become more perpendicular.

Cheers,
Bart
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: Jim Kasson on November 13, 2013, 11:05:13 AM
Micro-lenses are not an optical image forming device, they are condensers that change the angle of already focused incident light to become more perpendicular.

Bart, this is clearly stated (as usual for you), obvious (now, to me), and something I'd never thought of that way before.  Thank you for this insight.  And thanks for all you do for this forum.

Jim
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: BartvanderWolf on November 13, 2013, 11:56:36 AM
Bart, this is clearly stated (as usual for you), obvious (now, to me), and something I'd never thought of that way before.  Thank you for this insight.  And thanks for all you do for this forum.

Hi Jim,

You're welcome. I'm just trying to demystify some things, and explain them in terms of practical use.

This link (http://www.prolinx.co.jp/supplier/IDS/uEye_Manual_En/index.html?hw_fuellfaktor.html) explains the use of offset (no tilt involved) micro-lenses, including a slight color shift warning for truly telecentric lenses (constant magnification regardless of focus). Most lens designs are not truly telecentric though.

It's just that we do not know how much of a difference there is between the design of the Sony lenses (and their exit pupil distance), and OEM lenses. So there could be some effect, but there is also such a Color Cast effect with MF sensors without micro-lenses, and is handled by a Lens Cast Calibration applied during Raw conversion.

Cheers,
Bart
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: EinstStein on November 13, 2013, 07:31:52 PM
In the digital signal processing terminology the microlens is the sampler and integrator. It is OK too if you want to see it only the integrator part, ignore the sampler. This may better match your view that it is "only the condensor".
Back to your DSP 101 again, if you still have it, check out the window effect of the sampler and integrator, you should find the effect of the window functions. It matters a lot for the recovered signals, "reading, the final image".
Sorry for the boring engineering stuffs.
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: hjulenissen on November 14, 2013, 01:51:05 AM
In the digital signal processing terminology the microlens is the sampler and integrator. It is OK too if you want to see it only the integrator part, ignore the sampler. This may better match your view that it is "only the condensor".
Back to your DSP 101 again, if you still have it, check out the window effect of the sampler and integrator, you should find the effect of the window functions. It matters a lot for the recovered signals, "reading, the final image".
Sorry for the boring engineering stuffs.
I actually did "DSP 101" but I must admit that I don't get what you are trying to explain.

I see the sensel as a spatial sampler (turning continuous spatial data into a non-contiguous train of samples). I see the combined motion blur/lens PSF/diffraction/microlens/OLPF/sensel area as some spatial pre filter/integration. Are we discussing the same thing?

-h
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: hjulenissen on November 14, 2013, 01:55:32 AM
Micro-lenses are not an optical image forming device, they are condensers that change the angle of already focused incident light to become more perpendicular.

Cheers,
Bart
Is this what you are saying?:
(http://www.jiscdigitalmedia.ac.uk/images/microlens_big.gif)

Possibly irrelevant to this discussion:
Would you not say that the (multiple sensels) reading the signal from the micro-lens array in front of a plenoptic camera/the Canon 70D are part of an "optical image forming device"?
(http://home.eps.hw.ac.uk/~ryf1/T27_files/image004.jpg)
"The microlens array from a plenoptic camera is placed in front of a 20 pence coin to show scale, and the effect of repetitions that the array gives inside a camera.  Each microlens is 135microns in diameter, with a 0.5mm focal length."
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: BartvanderWolf on November 14, 2013, 05:42:33 AM
Is this what you are saying?:
(http://www.jiscdigitalmedia.ac.uk/images/microlens_big.gif)

Hi,

Yes, but it's only part of it. The simplified diagram shows tele-centric focused light, and the micro-lens helps to concentrate the light on the photosensitive areas instead of the supporting structures. When the chief ray angle is oblique, then the angle is changed more in the perpendicular direction as well.

In practice, there can also be a sort of aperture mask (perhaps simplified by just the 'walls' in the diagram) near the top of the sensel structure, which will cast a 'shadow' when light enters at an angle, and the micro-lens will reduce that by reducing the angle of light to become more perpendicular. More importantly, when the micro-lens is not centered above the sensel but rather somewhat offset in the direction of the center of the sensor array, it can be even more effective when the refractive index is closely matched to the amount of offset.

Quote
Possibly irrelevant to this discussion:

Plenoptic optics are indeed something different altogether.

Cheers,
Bart
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: EinstStein on November 17, 2013, 12:45:11 AM

Someone posted the following comparison.
Help yourself see how they perform.
 
//
The links below are from flickr courtesy of user ZhanQL

A7r

http://www.flickr.com/photos/inikon/sets/72157637668801615/

A7

http://www.flickr.com/photos/inikon/sets/72157637688730425/
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: ErikKaffehr on November 17, 2013, 01:52:36 AM
Hi,

According to Sony both A7 and A7r have tilted micro lenses.

The problem with the samples is not flange distance but lenses that are not calculated for digital sensors. Leica has the same issues, but they developed their own sensor with deeper wells and have bar codes on the lens that tell the camera about the lens they use and approximate aperture using a light metering trick.

The difference between the A7 and A7r is probably coming from the pixels being smaller on the A7r.

This has nothing to do with short flange distance nor to offset microlenses and a lot to do with distance of outlet pupil to sensor. Of course would the flange distance be significantly longer, they would not be able to viewfinder lenses on the camera, so problem would not arise. Leica R lenses, Canons, Nikons work just fine.

Best regards
Erik


Someone posted the following comparison.
Help yourself see how they perform.
 
//
The links below are from flickr courtesy of user ZhanQL

A7r

http://www.flickr.com/photos/inikon/sets/72157637668801615/

A7

http://www.flickr.com/photos/inikon/sets/72157637688730425/
Title: Re: Shorten the flange distance, then tilt micro-lens? why not just keep it longer
Post by: BartvanderWolf on November 17, 2013, 06:39:08 AM
Someone posted the following comparison.
Help yourself see how they perform.

Thanks for the examples. They are from lens designs made for film, not for digital sensors. Digital Leica cameras also have a problem with these lens designs, it would have been nice to see those as well (probably with even worse results than from the Sony's). Nothing to do with Sony (or Leica, or anybody else) in particular, just the wrong lens design for digital cameras.

Here (http://www.voigtlaender.de/cms/voigtlaender/voigtlaender_cms.nsf/id/pa_fdih7blk4u.html) you can see the optical design of the 21mm f/4 used in the sample images, a design for a very short flange to film distance with large negative lenses at the rear. Compare that to another 21mm (http://lenses.zeiss.com/camera-lenses/en_de/camera_lenses/slr-lenses/distagont2821.html) design, with positive elements at the rear, and proven usability with digital sensors in general. The Voigtländer 21mm f/1.8 also performs well on digital sensors, its design (http://www.voigtlaender.de/cms/voigtlaender/voigtlaender_cms.nsf/id/pa_21mm_f1_8_engl.html) has a number of positive lens elements at the rear.

Cheers,
Bart