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03-18-2008, 08:49 PM   #1
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How does an "A" lens indicate its ID?

There are two parts to my question:

(1) How does an "A" lens indicate its ID?
Looking at the rear of my A50/1.7 lens it has one single pin/contact. Twist it on, camera instantly knows what lens it is. How does the lens tell my camera three separate bits of info (50mm, A, 1.7) with just one pin? Is it a series of digital pulses, or one analogue pulse, or three analogue pulses in sequence? Or some mechanical means?

(2) Coupled this lens to my 2x teleconverter:
Despite TC having 6-7 pins it can't tell camera anything about the lens. Have to manually indicate 50mm, Av mode doesn't work (coz camera doesn't recognize it's an "A" lens), etc ... What gives, how come 6-7 pins cannot transmit whatever on the 1 pin on lens?

Thanks.

03-19-2008, 12:58 AM   #2
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For the contacts see here:

Features and Operation of the Ka Mount
(scroll down a bit for the table)

It does not transmit the focal length, which you have to enter by hand, only the min/max apertures.

Why the TC does not work, don't know. Clean the contacts, perhaps.
Try mounting the TC first on the lens and then on the camera.
03-19-2008, 01:49 AM   #3
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My A lens has two contacts.

Also keep in mind that the mount itself can be considered a contact.
03-19-2008, 05:43 AM   #4
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Thanks for the link, good reading.
However it doesn't gel with my tests. For example it talks about a pin is raised or lowered according to aperture ring on or out of "A", but I tried with two lenses: no pins moved at all.

Anyway ... I'll keep exploring.

03-19-2008, 05:47 AM   #5
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QuoteOriginally posted by Kguru Quote
Thanks for the link, good reading.
However it doesn't gel with my tests. For example it talks about a pin is raised or lowered according to aperture ring on or out of "A", but I tried with two lenses: no pins moved at all.

Anyway ... I'll keep exploring.
There IS a pin which moves up and down according to aperture ring setting, on my third-party A-lens.

Maybe on newer versions, there's an internal contact that touches the "A" pin, instead of moving the entire pin...
03-19-2008, 06:04 AM   #6
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The table gives for f1.7-22: "101*11"
This means that you can see two "pins" on your lens bajonett.
r2 ("0") is a plastic isolation and the * is the A-Pin. The others are just shortened by the metal bajonet itself.

This is an image of the A50/1.7 I found on ebay:
The little ball (the A-pin) should move up and down when you move the aperture ring out of the A-position.
03-19-2008, 06:53 AM   #7
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Thanks again Wieland & ftpaddict; it starts to make sense for me.

Maybe due to internal contact instead of pushing out the pin for "A", it doesn't connect with the recessed * pin on my TC hence camera doesn't know it's an A lens. Will try packing something into the recess to force contact.
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