Canon EOS EF mount pin readout!
 

Ever wondered if there are any ways to use the marvelous 85mm at f1.2? I mean not in the lowest of lights but outdoors etc.
As many of you already know twisting method will disable any focusing with many ring type USM lenses and using ND's seemed to be the only option and still valid for getting normal shutter speeds.

I've been wondering that with just placing a small transparent piece of tape on the last 3 pins of the lens will discard/disable aperture data but the focusing power will remain.
The tape should be placed on the right hand side of the lens when looking at it, if I'm not mistaken. At least so you can lock the aperture but use focusing motor on those fly-by-wire "L" series like the magical 85mm f1.2.

So, the Canon EOS EF mount pin readout at the camera body is:
(Left to right, looking at the front of the body)

1. VBAT
2. P-GND 3. P-GND (pins 2 & 3 are common on the lens)
4. VDD
5. DCL
6. DLC
7. LCLK
8. D_GND

Pin Functions explained:

VBAT - Motor power
P_GND - Motor power ground
VDD - Logic circuitry power
D_GND - Logic circuitry ground
DCL - Data from body to lens
DLC - Data from lens to body
LCLK - Clock

Data protocol: Motorola SPI; 8 bit serial; Such as the protocol used with the 68HC05 chip. (hint hint for FF makers) I assume the few RED EF mount makers use the same chip.

Experiment on a cheap lens first, as this so far is only in theory!

Cheers,
T

Thank you for the info. Maybe you can post a small photo of the tape as you've applied it? We will make this into a real cinema camera! :)

I tried some tape on a cheap lens. And then it disappeared. I hope it's not in the camera.

I won't be applying any more tape, unless there's a way to ensure that it stays put.

lol...that first statement was just worded in the most hilarious way.

I would seriously be tearing apart my camera looking for that piece of tape. Things like that bug me. I lost a lens cap once in my bag and after 5 minutes of tearing the thing apart I found it.

Jon: Sux .. most likely, when you mount the lens there is a friction point and the tape probably dislodged. Most likely, it's in your camera body.

I hope not. So far, there's no trace.

I tried it every way and it didn't work with 85mm 1.2L, no focusing power.

:(

So are you saying that this "taping method" would at least allow you to use the lens at 1.2, but with manual focus? That would be OK... similar to the twist method, but at least the lens is locked in place.

that is if the tape stays on... sorry John....

Oh, and a note to the wise... if you come across the old 85mm1.2 L going cheap, it had power assisted manual focus, so taping/twisting, means no focus on that baby...

New version, MKII 85 1.2 has also power assisted manual focus if I'm not mistaken, I have that EF 85mm 1.2 MKI and my colleague has MKII and this too can not manually focus on DOF adaptor for example...

T

thanks for the clarification. I was just going off the specs here

Canon Australia - EF 85mm f/1.2L II USM

that mention full time mechanical focusing. Shame.. looks like it will be the nikkor...

I've been thinking of getting some thin mylar, cutting it to just cover all the pins, and then punching holes where the GND pins are (2, 3, & 8). I'm hoping those three holes would keep it in place. Any thoughts?

I now have a better idea for how to use the mylar that involves no holes and will be much easier to insert and remove. If interested see http://www.dvinfo.net/conf/1002979-post13.html