what are the symptoms of sticking aperture blades?

on my recent road trip to and through Utah I noticed my 24-70L II intermittantly would throw a severely underexposed frame followed by one that was way overexposed. and then it would perform normally for awhile.

the problem could be worse in the heat because it seems like in the 100-degree days it was worse and in the 50 or so frames I shot in death valley the problem occurred maybe three times.

the lens is going in today but do these symptoms sound familiar to anyone? thanks.

Have you put on another lens since and see if it happened with any other lens? I wonder if it could be a failing shutter.

Weird that you wouldn't get an error message if it was the lens like "Error 01" or something. If no other lens does this, it would likely be the lens then.

Invertalon wrote in post #16991651
Have you put on another lens since and see if it happened with any other lens? I wonder if it could be a failing shutter.

Weird that you wouldn't get an error message if it was the lens like "Error 01" or something. If no other lens does this, it would likely be the lens then.

it's only with that lens. but I hadn't considered the weirdness of not giving error messages something that even my car does these days

You should try to replicate the problem with another lens. That would help to isolate the problem to either the lens or the body. Make sure the lens electrical contacts are clean and the buttons (for want of a better word) springy.

joedlh wrote in post #16991680
You should try to replicate the problem with another lens. That would help to isolate the problem to either the lens or the body. Make sure the lens electrical contacts are clean and the buttons (for want of a better word) springy.

I shot more than 3000 frames using all my lenses. the problem only occurs with the 24-70L II.

The easy way to test it is to stop the lens down to it's smallest aperture, then look down the lens from the front and push the DOF preview button a number of times to see if the blades are functioning properly.

EverydayGetaway wrote in post #16992153
The easy way to test it is to stop the lens down to it's smallest aperture, then look down the lens from the front and push the DOF preview button a number of times to see if the blades are functioning properly.

It would be, if the problem were repeatable. Ed suspects it was due to the high temperatures in Death Valley. He can't repeat them in SF and I will be the last to recommend heating up the lens in an oven!...

MakisM1 wrote in post #16992522
It would be, if the problem were repeatable. Ed suspects it was due to the high temperatures in Death Valley. He can't repeat them in SF and I will be the last to recommend heating up the lens in an oven!...

It would still eliminate the lens as being faulty in general. My first copy of the Samyang 85mm had sticky aperture occasionally and it was pretty easy to see looking down the lens.

EverydayGetaway wrote in post #16992539
It would still eliminate the lens as being faulty in general. My first copy of the Samyang 85mm had sticky aperture occasionally and it was pretty easy to see looking down the lens.

it's an intermittent problem, and I know from my day job those are the toughest to diagnose.

the bad news is I see where I had the problem once while using my fisheye. I don't know what to think now, dammit

ed rader wrote in post #16991609
on my recent road trip to and through Utah I noticed my 24-70L II intermittently would throw a severely underexposed frame followed by one that was way overexposed. and then it would perform normally for awhile.

the problem could be worse in the heat because it seems like in the 100-degree days it was worse and in the 50 or so frames I shot in death valley the problem occurred maybe three times.

the lens is going in today but do these symptoms sound familiar to anyone? thanks.

This is exactly the symptoms of a failing aperture diaphragm. I had this on my Sigma 28-300 on a very hot day in the sun. Sometimes after taking a shot stopped down, the iris wouldn't re-open although the camera thought that it had. The viewfinder is a bit dimmer of course but on a sunny day you don't always notice. The next shot is then metered with the iris partly closed but the camera thinks it is open so when you take the next shot, it is overexposed. After it cooled, it seemed ok.

You can check for it by putting the camera in Av or M mode and pressing the depth of field preview button repeatedly while looking into the end of the lens and trying different f-stops. It should be snappy and always reopening all the way at every f-stop. If not, you may want to get the aperture replaced.

I had a lens on my old film camera that was eventually diagnosed with sticking aperture blades. The symptoms were over exposed shots when shooting at any aperture smaller than f/5.6. The smaller the aperture that was required for the shot, the more over exposed the result would be. All down to the fact that the aperture blades would only close down to f/5.6 and then stick. Only shots requiring smaller apertures were affected, so initially it looked like an intermittent fault.

I had overexposure from sticking aperture blades in my old 35F2. The Canon repair ran me $109. The big deal was that this happened right before a birthday party. Now, the old 35F2 gets used as a travel lens when I want to go light or as a backup to,the IS version.
I should probably just sell the lens, but it is so sharp that I hate to part with it.

ed rader wrote in post #16992822
it's an intermittent problem, and I know from my day job those are the toughest to diagnose.

the bad news is I see where I had the problem once while using my fisheye. I don't know what to think now, dammit

So you did the DoF preview/small aperture test, and are not able to see any abnormalities at all? May have to try it next time you're in hot weather.

waterrockets wrote in post #16993373
So you did the DoF preview/small aperture test, and are not able to see any abnormalities at all? May have to try it next time you're in hot weather.

I shipped the lens off to canon and you know they'll change the assembly whether it needs it or not.

I have the 16-35L f5 IS coming Friday. what i'll do is use the hell out of that lens and see if the problems reoccurs. if so I have a camera issue.

ed rader wrote in post #16993564
I shipped the lens off to canon and you know they'll change the assembly whether it needs it or not.

I have the 16-35L f5 IS coming Friday. what i'll do is use the hell out of that lens and see if the problems reoccurs. if so I have a camera issue.

Good plan. Please let us know what you discover.