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addy landzaat View Drop Down
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Post Options Post Options   Quote addy landzaat Quote  Post ReplyReply Direct Link To This Post Posted: 19 June 2017 at 19:39
Originally posted by kefkafloyd kefkafloyd wrote:

The E-mount's throat is wider than Nikon F and Minolta SR (and is similar to some other FF 35mm mounts). Leica's SL mirrorless is only moderately (by 2mm) wider.
Interesting, jut checked Wikipedia and the Leica M is 44mm throat with 27.8mm flange focal distance. Sony (F)E-mount is 46.1mm throat with 18mm flange focal distance.
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Post Options Post Options   Quote artuk Quote  Post ReplyReply Direct Link To This Post Posted: 19 June 2017 at 21:43
Originally posted by QuietOC QuietOC wrote:

What advantage could there be to increasing the flange distance other than possibly making some lens bodies shorter? Lenses with empty tubes at the back like the FE 50/1.8 are not problems.


The further the lens rear elements are from the sensor plane, the easier it is to make the light strike the sensor at 90 degrees, the ideal for the light to pass through the microlens on the sensel and penetrate the well with the receptor inside to be registered as electrical charge. As lenses get closer to the sensor, and the lens throat / rear element is smaller, the more difficult it is to get light on the edges and corners of the frame to do this. So the light reaches the sensor at an angle, and yoi get problems with softness, colour shifts, vignetting and other issues. "Telecentric" lens designs try to beam the light onto the sensor at near the ideal 90 degrees. Short flange depths male this difficult, without forming an image deep inside the lens, having a large air gap between the rear elements and the sensor, and therefore forcing telecentricity. The smaller the lens mount, the harder to do this as you don't illuminate the edges and corners properly so are forced to make the light hit the sensor at an angle, causing the problems mentioned above. It's why older Leica lenses are terrible om digital and need lots of camera corrections and a specially designed sensor with sensels at an angle to face the central.axis through the lens to try and make sure they are illuminated correctly.
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kefkafloyd View Drop Down
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Post Options Post Options   Quote kefkafloyd Quote  Post ReplyReply Direct Link To This Post Posted: 19 June 2017 at 22:33
Originally posted by artuk artuk wrote:

Originally posted by QuietOC QuietOC wrote:

What advantage could there be to increasing the flange distance other than possibly making some lens bodies shorter? Lenses with empty tubes at the back like the FE 50/1.8 are not problems.


The further the lens rear elements are from the sensor plane, the easier it is to make the light strike the sensor at 90 degrees, the ideal for the light to pass through the microlens on the sensel and penetrate the well with the receptor inside to be registered as electrical charge. As lenses get closer to the sensor, and the lens throat / rear element is smaller, the more difficult it is to get light on the edges and corners of the frame to do this. So the light reaches the sensor at an angle, and yoi get problems with softness, colour shifts, vignetting and other issues. "Telecentric" lens designs try to beam the light onto the sensor at near the ideal 90 degrees. Short flange depths male this difficult, without forming an image deep inside the lens, having a large air gap between the rear elements and the sensor, and therefore forcing telecentricity. The smaller the lens mount, the harder to do this as you don't illuminate the edges and corners properly so are forced to make the light hit the sensor at an angle, causing the problems mentioned above. It's why older Leica lenses are terrible om digital and need lots of camera corrections and a specially designed sensor with sensels at an angle to face the central.axis through the lens to try and make sure they are illuminated correctly.


Note that this is more of a problem with sensor technology, toppings, etc than necessarily optics. The optics are trying to get around problems with the sensor.

If the sensor can be tailored to the lens (and vice versa), you'll have almost no distance between the two, like on the RX cameras.

There may be a sensor technology in the future (curved sensors) or other tech that negate the disadvantages that current sensor designs have with off-axis light.
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Cliff View Drop Down
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Post Options Post Options   Quote Cliff Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 15:16
"Note that this is more of a problem with sensor technology, toppings, etc than necessarily optics."

Seems this was an issue with film technology too. Common SLR flange distances ran from Konica at 40.7mm to Nikon at 46.5mm. Minolta A is in the middle of the pack at 44.5mm (mc/md @ 43.5mm). SLR makers seemed to favor 42mm throats, there are many at that diameter including Minolta.

Question, when did flange distance replace the registration distance nomenclature I learned years ago?
ContaxRF, Min7000i, Sony A100, A65, Nex5T, A7ii, A6500. 2 many lenses, mostly ordinary Minolta & 3rd party A, MC/D, other mf, vintage Vivitars & cats, LA-EA2,3,4 E16-50&55-210mm
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Post Options Post Options   Quote kefkafloyd Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 15:35
Originally posted by Cliff Cliff wrote:

"Note that this is more of a problem with sensor technology, toppings, etc than necessarily optics."

Seems this was an issue with film technology too. Common SLR flange distances ran from Konica at 40.7mm to Nikon at 46.5mm. Minolta A is in the middle of the pack at 44.5mm (mc/md @ 43.5mm). SLR makers seemed to favor 42mm throats, there are many at that diameter including Minolta.

Question, when did flange distance replace the registration distance nomenclature I learned years ago?


Common SLR flange distances were there because there was a mirror box in the way. Rangefinder flange distances were far shorter.

"Flange Distance" refers to the actual bayonet flanges of the mount, which may or may not be where the lens' backfocus actually registers. You could have rear elements that protruded into the mirror box for a closer registration distance, but you'd be forced to lock the mirror up (c.f. the Nikon ultrawide fisheyes).
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 17:06
Originally posted by kefkafloyd kefkafloyd wrote:

Common SLR flange distances were there because there was a mirror box in the way. Rangefinder flange distances were far shorter.

But they were never as short as the E-mount distance. Again, I assume there was a recognized 'happy medium' distance range that allowed the most flexibility in lens design. Even Micro 4/3 is longer!
 



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Post Options Post Options   Quote Bob J Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 17:18
One of the limiting factors for 35 rangefinder cameras was the depth of the film cassette. If you think about it, they would have had to do special fabrication to cope with a body depth at the left of the camera that was greater than at the mount.

Not a huge need to go much below that as they were not using really short focal lengths. Stuff that doesn't work so well on digital tends to go very deep into rangefinder camera bodies (like my Zeiss Biotar 28/2.8, which has a very protruding bulbous rear element).
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Post Options Post Options   Quote addy landzaat Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 17:22
Originally posted by Cliff Cliff wrote:

Seems this was an issue with film technology too. Common SLR flange distances ran from Konica at 40.7mm to Nikon at 46.5mm. Minolta A is in the middle of the pack at 44.5mm (mc/md @ 43.5mm). SLR makers seemed to favor 42mm throats, there are many at that diameter including Minolta.
From the link in my previous post it says the throat for A-mount is 49.7mm, SR mount (MC/MD) is 44.97mm. If the bayonet mouth is 42mm, M42 lenses wouldn't fit.
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Post Options Post Options   Quote Cliff Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 17:32
The article I was looking at had a surprising number of mounts at 42mm. Should have made me suspicious. But it was on the web, how could it be wrong? Interesting, that makes mc/md close to E in diameter.

On registration distances, my old Contax RF was 34.85mm, a little more than half way between E and A mounts.

Edited by Cliff - 20 June 2017 at 17:37
ContaxRF, Min7000i, Sony A100, A65, Nex5T, A7ii, A6500. 2 many lenses, mostly ordinary Minolta & 3rd party A, MC/D, other mf, vintage Vivitars & cats, LA-EA2,3,4 E16-50&55-210mm
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addy landzaat View Drop Down
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Post Options Post Options   Quote addy landzaat Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 17:46
Well, Wikipedia isn't flawless either, but at least it can be corrected by people in the know - and then again by people who don't know
Das Bild ist ein Modell der Wirklichkeit - Wittgenstein
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Post Options Post Options   Quote artuk Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 18:14
Originally posted by kefkafloyd kefkafloyd wrote:

Originally posted by artuk artuk wrote:

Originally posted by QuietOC QuietOC wrote:

What advantage could there be to increasing the flange distance other than possibly making some lens bodies shorter? Lenses with empty tubes at the back like the FE 50/1.8 are not problems.


The further the lens rear elements are from the sensor plane, the easier it is to make the light strike the sensor at 90 degrees, the ideal for the light to pass through the microlens on the sensel and penetrate the well with the receptor inside to be registered as electrical charge. As lenses get closer to the sensor, and the lens throat / rear element is smaller, the more difficult it is to get light on the edges and corners of the frame to do this. So the light reaches the sensor at an angle, and yoi get problems with softness, colour shifts, vignetting and other issues. "Telecentric" lens designs try to beam the light onto the sensor at near the ideal 90 degrees. Short flange depths male this difficult, without forming an image deep inside the lens, having a large air gap between the rear elements and the sensor, and therefore forcing telecentricity. The smaller the lens mount, the harder to do this as you don't illuminate the edges and corners properly so are forced to make the light hit the sensor at an angle, causing the problems mentioned above. It's why older Leica lenses are terrible om digital and need lots of camera corrections and a specially designed sensor with sensels at an angle to face the central.axis through the lens to try and make sure they are illuminated correctly.


Note that this is more of a problem with sensor technology, toppings, etc than necessarily optics. The optics are trying to get around problems with the sensor.

If the sensor can be tailored to the lens (and vice versa), you'll have almost no distance between the two, like on the RX cameras.

There may be a sensor technology in the future (curved sensors) or other tech that negate the disadvantages that current sensor designs have with off-axis light.


As I've already commented, some sensors angle the sensels towards the edges and corners towards the Central axis of the lens to get around this problem. It's best done where the sensor.and lens are a fixed pair, since trying to correct for a wide variety of interchangeable lenses may be rather non optimal (e.g. Makes telecenteic lenses worse!). The "problem" with small mounts is that the actual throat of the mount is rather smaller than the mount - in Full frame E mount, looking through the mount you can barely see the corners of the sensor - and therefore yoi have to "squeeze" the image through, meaning with short flange depth plus small throat telecentricity is poor without air gaps inside the lens to simulate a longer flange depth.
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Post Options Post Options   Quote artuk Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 18:16
Originally posted by sybersitizen sybersitizen wrote:

Originally posted by kefkafloyd kefkafloyd wrote:

Common SLR flange distances were there because there was a mirror box in the way. Rangefinder flange distances were far shorter.

But they were never as short as the E-mount distance. Again, I assume there was a recognized 'happy medium' distance range that allowed the most flexibility in lens design. Even Micro 4/3 is longer!


Quite - the 10mm difference between E mount and Leica M is substantial in this context. I am sure E mount was designed that way for the smallest possible body, as that seemed to be the design goal of several generations of NEX cameras.
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Post Options Post Options   Quote kefkafloyd Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 18:55
Originally posted by artuk artuk wrote:

Originally posted by sybersitizen sybersitizen wrote:

Originally posted by kefkafloyd kefkafloyd wrote:

Common SLR flange distances were there because there was a mirror box in the way. Rangefinder flange distances were far shorter.

But they were never as short as the E-mount distance. Again, I assume there was a recognized 'happy medium' distance range that allowed the most flexibility in lens design. Even Micro 4/3 is longer!


Quite - the 10mm difference between E mount and Leica M is substantial in this context. I am sure E mount was designed that way for the smallest possible body, as that seemed to be the design goal of several generations of NEX cameras.


Yes, but if you look at the construction of a Leica M film camera, there had to be room in the body for film and transport, which affects how you can construct the lens mount. Digital bodies have no need for that. And yes, Sony clearly went with what could be done with the smallest body, but Canon EF-M and Leica SL are within the ballpark for both flange distance and diameter. 2 mm difference (for either the throat or registration) is minor. It's still a difference, yeah, but it's not like the difference between Canon's EF mount throat and F-mount. Canon EF-M mirrorless may not be doing full-frame today, but since it's within the ballpark of E-mount it should be able to handle FF just fine.

Leica's flange distance also doesn't control the position of the rear element, either.. There are plenty of M lenses where the rear element sticks in farther than the bayonet. Look at the Leica 24mm f/3.8.

You can always make the rear of a lens longer, but you can't take away a mirror box or body constraints once it's baked in to the system. This, of course, is true for the flipside - you can never make a lens mount wider.

I don't see anything inherently wrong with an airgap in the back of the lens except for the fact that it makes the lens a little longer. That airgap also doesn't have to be exactly the length of what the mirror box used to be, it can be shorter. Obviously E-mount is supposed to bring size benefits, but it's not going to universally make every lens smaller. It just means that if you have the chance to make the lens smaller, you can take it versus being constricted up front like on A-mount. And if better sensors give better corner performance, then it's less of an issue.

I'm not saying the E-mount doesn't have challenges or complications, just that the "oh, the throat is SO NARROW!" is overblown.

Edited by kefkafloyd - 20 June 2017 at 19:08
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 19:29
Originally posted by kefkafloyd kefkafloyd wrote:

You can always make the rear of a lens longer, but you can't take away a mirror box or body constraints once it's baked in to the system. This, of course, is true for the flipside - you can never make a lens mount wider.

I don't see anything inherently wrong with an airgap in the back of the lens except for the fact that it makes the lens a little longer.

Different lenses require different physical dimensions. When you say you can always make the rear of a lens longer, that's something you might prefer to avoid especially if the lens is going to be kind of large to begin with. In essence, a short flange distance allows short lenses to be shorter, but probably requires long lenses to be even longer. If you have a few such long lenses, it would be beneficial to have that 'gap' built into the camera only one time instead. If you instead have several short lenses, the camera gap could be considered unnecessary and annoying.

This summary of standards has some interesting stuff on the flange distance decision for Micro 4/3:

'The flange back length has been reduced to about 1/2 that of the Four Thirds System. This is considered short enough to allow radical reductions in size and thickness, without causing problems with the lens drive and while still reserving space for accommodating the devices indispensable for digital SLRs such as the low-pass filter and the dust reduction mechanism, as well as devices likely to be adopted in the future.

This, together with the reduction of the lens mount diameter, has made it possible to reduce the thickness and size of SLR cameras without compromising the high picture quality.'


I haven't seen a corresponding statement from Sony concerning E-mount.
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