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12-31-2011, 02:34 PM   #16
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QuoteOriginally posted by violini Quote
Therefore, on a crippled lens mount of a DSLR, if the aperture ring of a A (or FA) lens is not set at "A" position, then it works just like a K or M lens and would need to use green button for metering (am I correct?).
Yes...this is correct.


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12-31-2011, 03:47 PM   #17
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Thanks, Steve for the answer. Another question I have is: when the lens is set at "A" position, which one controls the aperture, 1. the mechanical linkage at 9 O'clock position (when viewed from the front) of the crippled lens mount, or 2. the single electrical contact to the lens?
12-31-2011, 04:13 PM   #18
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The mechanical lever opens and closes the aperture always.
In the A position, the body stops the level in a calculated midway position that corresponds to the selected (in the body) aperture.
In non A position, the lens sets the limit and when the body releases the level all the way, it stops where the lens has set it.
12-31-2011, 04:25 PM   #19
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QuoteOriginally posted by violini Quote
Thanks, Steve for the answer. Another question I have is: when the lens is set at "A" position, which one controls the aperture, 1. the mechanical linkage at 9 O'clock position (when viewed from the front) of the crippled lens mount, or 2. the single electrical contact to the lens?
The mechanical linkage. This engages the "flipper" lever on the lens to stop down the iris diaphragm. As noted above by Demp10, the degree of lever movement varies according to body aperture setting when an "A-contact" lens is detected and is full range when not.


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01-01-2012, 04:19 AM   #20
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QuoteOriginally posted by stevebrot Quote
the degree of lever movement varies according to body aperture setting
I have always thought that using this could allow the camera to detect aperture setting without having to have another lever to go with the "real" aperture position lever on the lens. But perhaps these aperture-control levers vary too much between lenses to be useful for aperture-detection. The difference in position between settings can be tiny too. Oh well, I doubt there's any chance of them uncrippling the mount now anyway.
01-01-2012, 04:25 PM   #21
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QuoteOriginally posted by stevebrot Quote
I couldn't have said it better myself, though it is important to restate (forcefully) that even with an A-contact lens, the lens does not tell the camera what the current aperture setting is, only the max and min. As a result, when the aperture ring is off the A setting, the camera no longer controls the aperture and has nothing to display to the user except the shutter speed.

The lens NEVER communicates the set aperture to the camera except as the offset from maximum and that only on bodies without the crippled mount and by the mechanical linkage and not by the A contacts.
I don't see how this makes sense. The lens tells the body what the maximum aperture is (with A and newer lenses), and it tells the body how far from maximum aperture it is set. How is this not telling the body what aperture it is set at?

(Sure, it needs (trivial) math, and it's part electronic and part mechanical, but I refuse to believe this is a problem. My MZ-S agrees with me, showing me the selected aperture when I use the aperture ring on modern lenses. Even if it's only for F and newer lenses, but I believe this is for marketing reasons. The matrix meter works with A lenses when not in the A position on most MZ series cameras, and I could certainly make the firmware bits needed to make it display the aperture, so I must assume Pentax could too.)
01-01-2012, 05:05 PM   #22
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QuoteOriginally posted by drougge Quote
I don't see how this makes sense. The lens tells the body what the maximum aperture is (with A and newer lenses), and it tells the body how far from maximum aperture it is set. How is this not telling the body what aperture it is set at?
The body uses the A pin (#3 from left to right as you look at the camera mount) as a switch for the existence of binary pins that encode max/min aperture. K and M lenses do not have that pin so the camera always treats them as manual aperture lenses.

If an A, F or FA lens has the aperture set at the "A" marking, the A pin is engaged and connects with the body telling it, that this is an A lens with contacts. The body reads the binary pattern and ignores the aperture coupling ring; f-stops are controlled by the body via the aperture lever.

If the A pin is not engaged (as in all non "A" aperture positions) on an A, F, or FA lens, the camera thinks that this is an manual aperture lens and then ignores the pins and uses the aperture coupler.

Lenses without an aperture ring (like DA) have the A pin permanently engaged, therefore forcing the camera to treat them as Auto aperture lenses all the time.

You can test this yourself by using a K or M lens and shorting the third pin from the left with a bit of aluminum foil. The pin is a bit below the surface of the mount, so a manual lens does not make contact with it. The manual lens will make contact will all the other pins though and singe the mount is all metal, it will short them providing a "11 111" bit pattern to the body. This tells the body that this is lens with max F/1.2 and min F/22 no matter which lens is mounted. You can now "control" the aperture from the body but it will be all wrong exept at full open or full closed.
01-01-2012, 09:30 PM   #23
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QuoteOriginally posted by drougge Quote
My MZ-S agrees with me, showing me the selected aperture when I use the aperture ring on modern lenses.
Fascinating...I don't own an MZ-S, but according to the manual, the body will provide approximate f/stop setting for F and FA lenses. You learn something new every day. Does anybody know if this is the general case for KAF and KAF2 bodies (AF with non-crippled mount)?


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01-02-2012, 08:44 AM   #24
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QuoteOriginally posted by stevebrot Quote
Fascinating...I don't own an MZ-S, but according to the manual, the body will provide approximate f/stop setting for F and FA lenses. You learn something new every day. Does anybody know if this is the general case for KAF and KAF2 bodies (AF with non-crippled mount)? Steve
F, FA and DA lenses have electronics in them and an additional pin for digital communications. The original A mount had only 6 pins: one for the A setting, and 5 for a binary pattern for max/min aperture. All the SFx, ZX-x, MZ-x and later bodies, including of course all digital, have the extra "digital" pin so they can communicate with the lens directly. I suppose the presence of the digital pin implies that the lens is an F, FA or DA and aperture can be set by the camera.

I am not sure if the actual f-stop dialed on the lens is transmitted digitally, but definitely the min and max f-stops are (that's why you get variable max on zoom lenses and weird values e.g. F/1.9; the old pins cannot encode that). If the mount is not crippled then it is trivial for the camera to estimate and display the f-stop set on the ring.
01-02-2012, 05:22 PM   #25
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QuoteOriginally posted by demp10 Quote
If the A pin is not engaged (as in all non "A" aperture positions) on an A, F, or FA lens, the camera thinks that this is an manual aperture lens and then ignores the pins and uses the aperture coupler.
But this just isn't true. The other pins are still there, they still tell the camera what aperture range the lens has. For anything slower than f/1.2 this is possible to distinguish from an older lens. (Or for F and newer regardless of aperture range.)

As I said, the matrix meter works with A lenses when using the aperture ring on the better film bodies. The matrix meter needs to know the actual aperture, so obviously, the camera knows this. And there are even instructions for modifying M lenses so the matrix meter works, even though this doesn't make them A lenses in any other way.
01-02-2012, 05:59 PM   #26
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QuoteOriginally posted by drougge Quote
But this just isn't true. The other pins are still there, they still tell the camera what aperture range the lens has. For anything slower than f/1.2 this is possible to distinguish from an older lens. (Or for F and newer regardless of aperture range.)

As I said, the matrix meter works with A lenses when using the aperture ring on the better film bodies. The matrix meter needs to know the actual aperture, so obviously, the camera knows this. And there are even instructions for modifying M lenses so the matrix meter works, even though this doesn't make them A lenses in any other way.
I was referring to newer digital bodies. They do not read the 5 pins with min/max data unless the A and the digital pins are shorted. I have modified several manual lenses and I speak from experience.

For late film bodies with un-crippled mounts it should be possible to meter correctly with A, F and FA lenses if they read the pins and use the aperture coupler, but I am not familiar with their operation. They would work though only with primes and constant aperture zooms lenses. If the max f-stop is different at various focal lengths, then, only the digital pin can convey that information.

Regarding the modification of a K or M lens to allow matrix metering it is a mixed bag. Technically the meter operates after the modification and it is accurate at the max and min f-stop but is off by more than one stop in some cases at the intermediate apertures. K and M lenses do not have linear aperture levers and the bodies use linear movements.
01-02-2012, 06:18 PM   #27
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On my MZ-6, the body knows the aperture setting on the ring in F and FA lenses including zooms, but not on A series of lenses. (DSLR s have crippled lens mounts, therefore won't know the setting on aperture ring. MZ-S cannot operate on Av-mode using ring-less lens.)

Last edited by violini; 01-02-2012 at 06:44 PM.
01-02-2012, 07:02 PM   #28
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QuoteOriginally posted by demp10 Quote
I was referring to newer digital bodies. They do not read the 5 pins with min/max data unless the A and the digital pins are shorted. I have modified several manual lenses and I speak from experience.
I'm well aware of the limitations of the crippled mounts. I was however not speaking of those. (As I thought was clear.)

QuoteOriginally posted by demp10 Quote
Regarding the modification of a K or M lens to allow matrix metering it is a mixed bag. Technically the meter operates after the modification and it is accurate at the max and min f-stop but is off by more than one stop in some cases at the intermediate apertures. K and M lenses do not have linear aperture levers and the bodies use linear movements.
This is not what I (or the page I linked to) am writing about. You are writing about modifying the lenses so the camera believed they are A lenses set to the A position. I am writing about modifying them so they are like A lenses set to some numeric aperture. The handling of this is completely different. The modification I am writing about makes no difference at all on a crippled mount camera, and works 100% perfectly on uncrippled mounts, because they will always release the aperture lever fully, stopping the lens down to the aperture set on the ring. Only meter operation is affected.

QuoteOriginally posted by violini Quote
On my MZ-6, the body knows the aperture setting on the ring in F and FA lenses including zooms, but not on A series of lenses. (DSLR s have crippled lens mounts, therefore won't know the setting on aperture ring. MZ-S cannot operate on Av-mode using ring-less lens.)
I don't have that camera, so it's possible you are right, but I'm making the argument that at least on the MZ-S the body does know the aperture on A lenses when using the aperture ring (except it might be wrong on variable aperture zooms), it just doesn't display it in the viewfinder. I believe this to be a decision made by marketing, not for any technical reasons.
01-02-2012, 09:33 PM   #29
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QuoteOriginally posted by drougge Quote
And there are even instructions for modifying M lenses so the matrix meter works, even though this doesn't make them A lenses in any other way.
Thank you for posting the link to Mark Robert's excellent discussion the subject. That page is one of the best references on the Web in regards to "A" contacts and what they do and do not do.


Steve
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