I was shooting with my DRebel and Sigma 170-500mm f/5-6.3 today. I was shooting wide open, at 500mm so my max aperture should have been f/6.3. I looked in my viewfinder and it said I was shooting at f/5.6. (Exif data also says 500mm @ f/5.6.) I zoomed back to 170mm oped it all the way and it said I was at f/5.0 as expected.

So then I stuck that same lens on my Elan 7N to see if it said the same thing. At 500mm I got the same reading, f/5.6. Then I zoomed back to 170mm and checked the aperture and it said f/4.5. Still using the Elan, I zoomed out to 500mm and it said I was at f/5.6 and I tried to stop down ot f/6.3, and the next click down went to f/6.7, whats up with that? When I do this with the DRebel it goes from f/5.6 to f/6.3.

Have I lost you yet?

Next I zoomed out to 500mm and set the apperture to f/6.3 with the DRebel, and pressed the DOF preview button, and it stopped the lens down. If f/6.3 is the max, according to the lens, I shouldn't have noticed a change in the viewfinder when I pressed the DOF preview button, but I did. I zoomed back to 170mm, and set the apperture to f/5 and pressed the DOP preview button, and again, it stopped down.

So how did my lens magically go from an f/5-6.3 to a f5.0-5.6 on my DRebel, and to an f/4.5-5.6 on my Elan 7N?

Maybe the Sigma lens isn't talking to the Canon properly.
Perhaps the contacts on the lens?

Maybe the Sigma lens isn't talking to the Canon properly.
Perhaps the contacts on the lens?


I thought about that last night, but I was too tired to experiment with it. I will try cleaning the contacts today and see if that helps. Thanks PAul!

I cleaned the contacts, on both the lens, and the camera and it still says the same thing. I cleaned them with a pencil eraser, and with some alcohol... The lens seems to be working and meeting fine, so it's not a huge deal at the moment. Just curiouse as to what would cause this. It's never been dropped or mistreated in any way.

I cleaned the contacts, on both the lens, and the camera and it still says the same thing. I cleaned them with a pencil eraser, and with some alcohol... The lens seems to be working and meeting fine, so it's not a huge deal at the moment. Just curiouse as to what would cause this. It's never been dropped or mistreated in any way.

Just a wild guess here... Sigma, for some reason, has to do a lot of "rechipping" to make their lenses work properly with Canon cameras. It may be that the lens is just a little too old for these cameras and is not speaking to them correctly. Rechipping is easy for Sigma to do and they usually do it for free. The downside is that the lens has to be sent to them.

I don't know, maybe?

I have thought about that too, but have not contacted sigma about it yet. I plan to tho. I have had the lens for a few years now, and this is the first time I have ever noticed this. Not that that means anything tho. I have heard of people using Sigma lenses and everything works fine, then that one time...

I had a (for a very short time...) Sigma 500 f7.2, or something like that. It read wrong, or differently at least, on my Nikon. I didn't really worry about it too much because it seemed to expose properly for whatever reason. Like in your case it was pretty close, but not exactly what it said it was.

I had a (for a very short time...) Sigma 500 f7.2, or something like that. It read wrong, or differently at least, on my Nikon. I didn't really worry about it too much because it seemed to expose properly for whatever reason. Like in your case it was pretty close, but not exactly what it said it was.

Yeah, I'm not too worried about it since it seems to be working fine. I did write to Sigma to see what they have to say about it and I'll post the responce I get here. I dought I will send it in to get if rechipped (if that's the problem), unless they offer to do it for free, or if they say that it's the start of something serious that could lead to a major problem.

It took a while to get a reply from Sigma, but here is what they had to say about it.

If the camera and this lens are performing together differently now than before, we don’t know why there should be a change. But, if the camera and this lens have always performed this way, we would say it is normal, probably a limitation of the digital aperture display. The important thing is that the pictures are properly exposed.