70-200mm shooting too light

[sooziesundlun]

So I am a professional photographer, using a Canon 70mm-200mm lens in my studio and at weddings.  I've noticed a severe lightness when using the lens that hasn't been there before.  In the past few days, I've noticed the photos being slightly overexposed, while when I use my normal wide-angle lens, the settings look perfect.  Does anyone have any insight into what could be causing this?

[hsbn]

do you have sample images? what program do you use to process your photo? See if Peripheral Illumination Correction has been turned on for the 70-200 lens

[TCampbell]

We would really need to be able to see some sample images for both lenses in the identical lighting and with EXIF data included.

It's easy to fool a built-in light meter because it has to rely on "reflected" light from the subject. Some materials are obviously more reflective than others.

The metering mode (evaluative vs. center weighted vs. spot metering) will also make a tremendous difference as well.

If I shoot a concert (typically extremely dark except for bright lights on the performers) then an "evaluative" metering mode will tend to over-expose because it's trying to improve all the blackness ... and this tends to blow out the well-illuminated performers. But if I use "spot" metering and put the spot on a critical element (such as the performer's face) to lock the exposure in, I'll get a completely different result -- and this is normal.

[amfoto1]

How old is the lens? It is possible the lens aperture is sluggish and not closing quickly enough to give a correct setting at the instant of exposure.

There are several possible reasons for this...

The easiest thing would be if the lens' electronic contacts just need a cleaning. Try wiping them with a clean, lint free rag lightly dampened with a few drops of isopropyl (rubbing) alcohol. Often this is all that's needed. Hopefully that's the case with yours, too... since it's a quick, easy fix that you can do yourself.

But there are other things that can effect the aperture's performance.

Oil on the blades is the classic and most common problem with all lenses that utilize the type of diaphragm that Canon (and most DSLR) lenses use. The oil "migrates" from elsewhere in the lens, perhaps from the grease used on the focusing or zoom mechanisms, and might be due to the lens getting hot in the sun or just from age. The aperture blades are designed to run dry, without any lubrication. Any oil on them makes them sticky and sluggish, causing exposure errors.  

It also can be failing electronics... either those that actuate the aperture itself or the connectivity between the lens and camera. Since other lenses seem to be working okay, I'd suspect it's your lens at fault and not your camera.  

These latter two issues would require a trip to Canon repair facility to have the lens checked and, if needed, serviced.

But hopefully it's just that the electronic contacts need cleaning.

***********
Alan Myers

San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
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