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07-30-2012, 01:23 AM   #1
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Why have my DA lenses still the aperture simulator pin

All DA lenses I own, mostly the kit zooms, still have the aperture simulator pin.
It is fixed in the smallest aperture position, so an older film body from before the A contacts generation gets the right exposure information, but that is rather silly, these DA lenses are quite useless on bodies who can't control the aperture.
No DSLR can read this pin on DA lenses, but you need to have a hole there, to prevent damage when mounted on older converters and extension tubes etc. but thats it, no need to make a long slit for communicating the smallest aperture.

So, if these lenses are useless on camera's which need that pin, and have no functions on the 'crippled KAF' mount DSLR bodies,
knowing that manufacturers strip anything whats not there for a function or marketing, why is this information pin still there ?

07-30-2012, 01:35 AM   #2
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If it's the stop-down lever you are refering to, then it's used to stop down the lens on all Pentax K-mount cameras, including DSLR and K-01.
07-30-2012, 02:06 AM   #3
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QuoteOriginally posted by Fogel70 Quote
If it's the stop-down lever you are refering to, then it's used to stop down the lens on all Pentax K-mount cameras, including DSLR and K-01.
No, I mean the aperture simulator pin.

To prevent further confusion, this pin :


To comparre with an aps-c sigma lens:


Sigma clearly thought, why bother, just a small hole to prevent damage when mounted on something its useless on.
07-30-2012, 02:32 AM   #4
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Ok that one. I guess Pentax done this not risking damage putting the lens on a "uncrippled" K-mount camera.

07-30-2012, 06:08 AM   #5
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As glasbak already said, it's not merely to "prevent damage", as just an empty slot would suffice for that purpose. The "pin" in the slot is obviously there to communicate an actual aperture to a camera with a non-crippled mount. The extra "holes" the pin could be put in suggests that the plastic part with the holes is used (or was expected to be used) in several lenses with different apertures. It can't be moved without dismantling the mount, so I'm guessing it's not there to allow customization of the reported aperture.
I've always thought this pin was interesting too. I really can't come up with any explanation that works. Allowing Av operation on very old (pre-KA) film cameras (or newer ones using no-contacts tubes etc) seems like far more trouble than it's worth. I'm not sure if newer film cameras depend on the aperture lever being in the smallest position when the aperture ring is in the A position, but maybe some do. Either way, you'd only be able to be able to shoot fully stopped down, and they are crop lenses anyway, so pretty useless for film.
All Pentax digital K-mount cameras (other than the prototype) have had a crippled mount, so this pin can't be for them. Even if they weren't crippled, the aperture information is transferred digitally, making the pin redundant.
07-30-2012, 07:19 AM   #6
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Another reason could be that they don't want to introduce a new version of the mount. Screwdrive lenses without the pin would be something like "double crippled" KAF2 mount. BTW the Sigma lens is a KAF3 mount lens as it don't have screwdrive, maybe Pentax KAF3 mount lenses is done the same way?
07-30-2012, 09:05 AM   #7
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QuoteOriginally posted by glasbak Quote
All DA lenses I own, mostly the kit zooms, still have the aperture simulator pin.
It is fixed in the smallest aperture position, so an older film body from before the A contacts generation gets the right exposure information, but that is rather silly, these DA lenses are quite useless on bodies who can't control the aperture.
No DSLR can read this pin on DA lenses, but you need to have a hole there, to prevent damage when mounted on older converters and extension tubes etc. but thats it, no need to make a long slit for communicating the smallest aperture.

So, if these lenses are useless on camera's which need that pin, and have no functions on the 'crippled KAF' mount DSLR bodies,
knowing that manufacturers strip anything whats not there for a function or marketing, why is this information pin still there ?
its there so that even the most basic camera like a K1000 will at least meter correctly.

if it was not there, then open aperture metering on K&M cameras would get it wrong.
07-30-2012, 12:36 PM   #8
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The pin is where it would be if the lens had an aperture ring and it was in the A position. So I think some older cameras with aperture simulators might expect that behavior. The simulator is spring-loaded and with no pin, the camera would not think the lens is in the A position. The pin might help my P3n work in program mode with a DA lens.

The DA series shouldn't need most of the aperture contacts either, as the aperture information is sent through one pin now. I don't have a lot of new lenses but I think the mounts might be standardized now. Maybe it would cost more to change the tooling than eliminate unnecessary pins.

07-30-2012, 12:57 PM   #9
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I have wondered this myself. Legacy stuff for sure.
07-30-2012, 01:40 PM   #10
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QuoteOriginally posted by Just1MoreDave Quote
The pin is where it would be if the lens had an aperture ring and it was in the A position. So I think some older cameras with aperture simulators might expect that behavior. The simulator is spring-loaded and with no pin, the camera would not think the lens is in the A position. The pin might help my P3n work in program mode with a DA lens.
I am not so sure about cameras checking for the A position, but more that cameras with no A setting absolutely need to know minimum aperture which is whwre the A setting puts them
QuoteQuote:

The DA series shouldn't need most of the aperture contacts either, as the aperture information is sent through one pin now.
no it is sent through 6 pins, the single data pin is for focal length, lens information, and focusing data for the AF
QuoteQuote:
I don't have a lot of new lenses but I think the mounts might be standardized now. Maybe it would cost more to change the tooling than eliminate unnecessary pins.
aside from that it is for minimum usability on older bodies.
07-30-2012, 02:11 PM   #11
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Aperture information must be transmitted digitally too - minimum and maximum aperture can both change when zooming.
07-30-2012, 02:23 PM   #12
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The A position is signaled by one of the contacts shorted to ground.
I am fully aware that this pin on the right position is required for correct metering on pre-A bodies, but they will only work on those bodies at the smallest aperture, and even apart from the too small APS-C image circle, this makes the lenses without aperture ring practically useless on these bodies
So, I do not understand why Pentax maintains this backward compatibility pin, when there is no practically use for it.

About the lens contacts,I suspect dual use of the classical A contacts, Aperture information for the older bodies, digital serial communication for the later generations.
The extra pin introduced in the KAF mount is probably the power line for the chips in the lens.
07-30-2012, 03:03 PM   #13
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QuoteOriginally posted by Lowell Goudge Quote
no it is sent through 6 pins, the single data pin is for focal length, lens information, and focusing data for the AF
The actual aperture information is sent through the seventh pin, along with the focal length, MTF (where supported), etc. You need this pin on a variable aperture zoom to communicate the wide-open aperture, otherwise your DSLR will think your 2.8-5.6 lens is always a 2.8, where the 2.8 is signaled through a few of the first 6 pins. The first 6 pins are old technology, only the 7th pin is really digital.
07-31-2012, 01:58 AM   #14
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I have used my DA16-45 for night shots on an ME body, so I'm glad they didn't make it completely useless (because I had a K5 with me as well, and didn't bring a film wide). I also think it's quite likely that bodies like the MZ-S will meter incorrectly in A mode if the pin is not in the right position.

And regarding the pins glasbak is right and several people are wrong, I am completely sure several old pins (not just the new one) are used for digital communication. (Try isolating them on your DSLR and notice that no digital communication works.)
07-31-2012, 05:11 AM   #15
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QuoteOriginally posted by drougge Quote
I have used my DA16-45 for night shots on an ME body, so I'm glad they didn't make it completely useless
Nightshots at F22, or daytime shots which look like nightshots because of the F22.
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