20-35mm 3.5-4.5 USM underexposes 1/3 stop

[chachi_arcola]

I just bought a 20-35 USM second hand and did a head-to-head test

with my 24/2.8 Canon lens at all apertures. Used an EOS 5, MLU,

Bogen 3021 tripod, Arca Swiss B1 head, ambient light. No filters,

dedicated lens hoods on both. Provia 100 shot at 100 and processed

normally at A&I here in L.A. Used evaluative metering, AF set to

center focusing point. Shot the side of my apartment building, a

flat subject, about 20 feet away. Both lenses autofocused to

infinity.

 

Here's what I found out. At 24mm, sharpness of the zoom at f/8 -f/11

was too close to the prime (at the same apertures) to differentiate.

Many straight lines in the photo, but distortion on both lenses was

negligible. Contrast maybe a bit better on the prime, but not

considerably so. The zoom looked a touch warm compared to the prime,

as though it had an skylight or 81A filter on it. Not objectionable,

but it was there.

 

What surprised me the most is that the zoom looked to be about 1/3

stop underexposed on about 1/2 the slides. I have heard reports of

this same phenomenon with this lens, and seen a head-to-head test vs.

the 16-35L which also showed the 20-35 to underexpose.

 

Has anyone else experienced this? If so, with what bodies? The lens

is good enough that I'm tempted just to dial in an extra half-stop of

compensation and forget about it.

[jbq]

Out of curiosity - did you meter TTL or did you just manually dial in the same EV for both lenses?

 

It's possible (I just said possible) that the zoom may lose more light than the prime at the same aperture because of the extra surfaces (i.e. extra reflections).

[canon man]

If its consistant the nset exposure comp when using that lens.