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07-31-2012, 05:38 AM   #16
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QuoteOriginally posted by drougge Quote
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.)
Well, that isn't isn't really conclusive. Did you isolate them one at a time or all together?
There must be some connection that provides power to the lens. I'm guessing all the pins are pulled high, with the camera detecting when they are held low by the lens. Presumably any of them could be used for power by the lens, but each individual lens might use only one, or several. Isolating whatever it does use would mean no power, and hence no digital communication.

07-31-2012, 05:56 AM   #17
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QuoteOriginally posted by Moo Quote
Aperture information must be transmitted digitally too - minimum and maximum aperture can both change when zooming.
While it is possible to do this, and I can't obviously comment on the data pin protocol, they had variable aperture lenses long before the 7th / data pin appeared, and many of these had aperture contact arrangements that changed when zooming. it was possible because of the way the coding was done, for the first 6 pins, that they could with sliding switches change the aperture as the zoom changed. I took apart one scrap AF sigma lens that I bought to get the mount, that had this arrangement, where it would recode the pins as you zoomed.
07-31-2012, 06:39 AM   #18
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QuoteOriginally posted by Lowell Goudge Quote
it was possible because of the way the coding was done, for the first 6 pins, that they could with sliding switches change the aperture as the zoom changed.
I was wondering about that, but this is the first mention I've seen of it being used. Is it a third-party-only "trick" or do Pentax use it too?
07-31-2012, 07:08 AM   #19
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There is lot of incorrect assumptions in this thread on how the original 6 contacts work. Please look at Bojidar Dimitrovs pages on this. In short, one of them signal the A position (yes or no). Five of them constitute a binary code for the min and max aperture. But non of them transmit any signal. It is a simple matter of conduction or non-conduction. Remember that non of the A generation lenses contain any electronics. In some sense this technical solution is more mechanical than electronic. It is the position of the pins and the material that is important.

The 7th contact was introduced with the KAF mount and is the only contact that actually transfer a signal, which use a serial signal protocol. I've seen some people claim that it is hybrid of digital and analog signal since in some part of the signal cycle the actual voltage level matters. The actual exact aperture setting is included in this signal. From the F generation lenses all lenses include a chip that communicate with the camera through this 7th contact.

Power is transferred through the two contacts that was introduced for the power zoom lenses, which are no longer used to power the zoom but to power the focus.

07-31-2012, 07:39 AM   #20
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No, no... I don't mean power for focus, which is what the power zoom contacts are used for now. I mean power for the chip you mention. This must (IMHO) be provided by one or more of the original 6 contacts.
07-31-2012, 07:46 AM   #21
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QuoteOriginally posted by Moo Quote
No, no... I don't mean power for focus, which is what the power zoom contacts are used for now. I mean power for the chip you mention. This must (IMHO) be provided by one or more of the original 6 contacts.
There is no power sent through the six (or five) A contacts. If you mean to be taken seriously on this, please show a measurement of this power.
07-31-2012, 07:56 AM   #22
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I will when I get a chance... But if the power does not come from those contacts, where does it come from? Do you not agree that the chip must be powered somehow? There isn't a battery in the lens, so the power must come from the camera. Also in order to detect the status of those original pins in pre-digital cameras, there must be some power, if only a tiny amount.
07-31-2012, 08:28 AM   #23
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QuoteOriginally posted by Moo Quote
I was wondering about that, but this is the first mention I've seen of it being used. Is it a third-party-only "trick" or do Pentax use it too?
I am not sure what all went on with variable aperture A lenses, as I have none.

I tried bypassing the data pin only on my Da18-55 and it shows up as F-- so on the DA they definitely use data pin for transmission of aperture as you zoom.and this goes back to the FA series as far as I can test

07-31-2012, 09:47 AM   #24
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QuoteOriginally posted by Moo Quote
Also in order to detect the status of those original pins in pre-digital cameras, there must be some power, if only a tiny amount.
Are you serious?
07-31-2012, 10:05 AM   #25
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QuoteOriginally posted by Douglas_of_Sweden Quote
Are you serious?
Yes... How else could it test for electrical conductivity (which I hope we agree is how the pins function) without the flow of some electricity?
07-31-2012, 10:06 AM   #26
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I find it unlikely that a variable zoom from whatever generation changes te classical A contacts aperture range/value information during zooming, no pentax variable zoom from the A series I have ever encountered does that, so it is probably not needed for correct operation.

Several years ago I measured the current the bayonet contacts of a SFXn could deliver when shorted to the bayonet metal.
The F series extra pin could supply significant more current than any of the classical A pins, so this is very likely the power source for the chip in the lens, and consequently not the serial data pin, that could be one or more of the other pins (in/out/clock who knows?).
I posted this info on a Pentax forum, maybe even this one, I will have to search.
07-31-2012, 11:25 AM   #27
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QuoteOriginally posted by Moo Quote
Well, that isn't isn't really conclusive. Did you isolate them one at a time or all together?
There must be some connection that provides power to the lens. I'm guessing all the pins are pulled high, with the camera detecting when they are held low by the lens. Presumably any of them could be used for power by the lens, but each individual lens might use only one, or several. Isolating whatever it does use would mean no power, and hence no digital communication.
I isolated them individually, and also tried shorting them. Not all are required, but more than just the new one and one more.

And as I pointed out in another thread, also with people for some reason not believing me, the MZ-60 (which is not to be confused with any other MZ camera) features exactly five contacts on the lens mount, and does not support A lenses. Since it does not support A lenses (or earlier), why would it have five contacts if not all five were used on modern lenses? (I think one of these might be ground, because the mount is plastic.)

QuoteOriginally posted by Douglas_of_Sweden Quote
There is no power sent through the six (or five) A contacts. If you mean to be taken seriously on this, please show a measurement of this power.
As has been pointed out there needs to be a pullup to detect if they are shorted. It measures between 0.01V and 0.08V on my K20, which is surprisingly low. Possibly it pulses a higher currect, I don't have a scope available to check.

And obviously one of them will be power for the chip in the lens once the camera determines that such a chip exists. (And just as obviously, it's not going to be wasting that power by letting it be shorted to ground when an old lens is attached.)
07-31-2012, 12:03 PM   #28
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QuoteOriginally posted by drougge Quote
It measures between 0.01V and 0.08V on my K20, which is surprisingly low. Possibly it pulses a higher currect, I don't have a scope available to check.
Did you tap the exposure button just before measuring ?
07-31-2012, 12:07 PM   #29
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QuoteOriginally posted by glasbak Quote
Did you tap the exposure button just before measuring ?
Of course I did. (Doesn't seem to make any difference though.)

Last edited by drougge; 07-31-2012 at 12:07 PM. Reason: spelling
07-31-2012, 12:28 PM   #30
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QuoteOriginally posted by drougge Quote
And as I pointed out in another thread, also with people for some reason not believing me, the MZ-60 (which is not to be confused with any other MZ camera) features exactly five contacts on the lens mount, and does not support A lenses. Since it does not support A lenses (or earlier), why would it have five contacts if not all five were used on modern lenses? (I think one of these might be ground, because the mount is plastic.)
Very interesting. It's m1 and m2 that are missing, the ones that would determine the minimum aperture on an A lens.
I agree... As they removed other contacts for this camera, and it doesn't support the old lenses, it follows that the remaining pins must be necessary in one way or another for "digital" F lenses.
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