Help w/ Sigma Lens Aperture & Canon 10d

[stevenlmas]

I have a Sigma 28-105mm F2.8 Lens for my Canon 10D that I bought used from B&H last Spring. The lens was (and still is) in excellent condition and appears to be fairly new. The lens was working fine when I bought it and through most of the year. A couple of weeks ago I was shooting in manual mode and tried to set the aperture to 2.8 but the lens would not open past 4.0.

I've tried:
Turning the barrel all the way in and out a few times
Turning off the camera and re-seating the lens
Cleaning the contacts w/ an eraser
Cleaning the contacts with alcohol
Formatting CF/Using different CF cards

All without success...
Any ideas or similar experiences/resolutions would be most appreciated.

Cheers!
Steve

[Trevor Ash]

That lens is a variable aperture lens. The max aperture at wide angle is different that the max available aperture at full zoom.

Try this experiment:

1. Set the camera to manual metering.
2. Set the lens to 28mm and set the aperture to 2.8
3. Set the lens to 105mm and look at what happened to the aperture.

If you tell me that after setting the lens to manual and 28mm that you then coudln't set it to f/2.8 then my guess is that there's something wrong with the lens or camera.

[stevenlmas]

Thanks for taking the time to respond, Trevor. I tried this experiment before but to be certain I tried it again last night following your instructions exactly, and I am still unable to get the aperture to 2.8.

What was that you said about Nikon??? ; ). Unfortunately I recently invested in two more Canon mount lenses so I'm not going to ba able to switch anytime soon...

Season's Greetings...
Steve

That lens is a variable aperture lens. The max aperture at wide angle is different that the max available aperture at full zoom.

Try this experiment:

1. Set the camera to manual metering.
2. Set the lens to 28mm and set the aperture to 2.8
3. Set the lens to 105mm and look at what happened to the aperture.

If you tell me that after setting the lens to manual and 28mm that you then coudln't set it to f/2.8 then my guess is that there's something wrong with the lens or camera.

[paulnj]

I think Trevor is RIGHT about the lens actually being a 28-105 VARIABLE aperture lens with F2.8 being available at shorter (wider) focal lengths and F4 being wide open at 105. Tamron is the ONLY maker of a true 28-105 F2.8 lens that I KNOW off.

Is this your lens?

http://www.bhphotovideo.com/bnh/cont...=129503&is=USA

IF not a 28-105 F2.8 constant lens would cost over that new lens's price SIGNIFICANTLY in even OK condition ;)

IF you can not get your lens to 28MM F2.8 then YES the camera / lens has a problem.

REMOVE THE LENS FROM CAMERA If you unlock the aperture ring(most lock) and MANUALLY can move the aperture to F2.8 setting WHILE at the 28MM focal length then we know your ring and blades are good. That would leave THE ELECTRICAL CONNECTIONS between camera and lens(meaning either ones electronics) mostlikely. We need to leave that 1% user error that ALL of us run into at times though ;)

[stevenlmas]

Thanks, Paul. I'll give that a crack when I get home. I'm pretty sure the lens you linked to is the one I have.

[stevenlmas]

I can't manually change the aperture with the lens unmounted. I think the problem may be electronic...

Arrrgh. Guess I'm going to have to try to contact Sigma.

[paulnj]

"I can't manually change the aperture with the lens unmounted"

Yes you can

there is a lock on the RIGHT side of the aperture ring.

the aperture ring itself has grooves going long ways and the lock has grooves the other way

move that lock towards the lens mount and the ring will click into each stop freely.

remember to relock the ring at the smallest aperture when you are done though, as that setting is what your camera needs to open and close the aperture automaticly .

THIS WILL NOT IN ANYWAY HARM YOUR LENS BTW

Sigma tech service will tell you just what I have I bet and they are quite helpful from my experience.

[Lionheart]

What was that you said about Nikon??? ; ). Unfortunately I recently invested in two more Canon mount lenses so I'm not going to ba able to switch anytime soon...

Season's Greetings...
Steve

Oh, you can always switch. There's always e-bay and someone waiting just for the items you have now.
... and this from a Canon user ;)