2 Canon 24-70 f/4 L IS with different exposure readings

Tried two different Canon 24-70 f/4 L IS at a local,shop.
Both had different exposure readings.
Manual mode, constant aperture, meter is set to "Proper Exposure" no compensation.
Difference is 1/3 Stop brighter.
Shutter 1/50 compared to 1/40 for example.
Does this new lens tend to run a bit brighter.
Thanks.

curious how were you testing two lenses at the same time with the exact same framing?

Tripod, swap lenses back and fort, not just one reading per lens. Readings at 24, 50 and 70. Not the most scientific, but consistent readings.

I can't imagine how this could possibly affect anything. You will likely never be using the same two exact lenses, on one body, pointed at the same subject at the same time. Every scene you will ever point your camera at will be different than the last. Expose accordingly. I have several lenses that seem to give best exposures at +1/3EC. Some not. Nothing consistent, though. Then again, maybe its not the lenses.

Buy the brighter one. It's centered better.

Nick5 wrote in post #17823452
Tripod, swap lenses back and fort, not just one reading per lens. Readings at 24, 50 and 70. Not the most scientific, but consistent readings.

gotcha. interesting, but keep in mind it could be a very insignificant difference and rounding "errors" forced one camera up and one down. What I mean is that the two lenses could be 1/10 of a stop different but one lens is just a tiny, tiny bit different in it's light transmission.


no window light at all?

To really find out, shoot two picks, one with lens and use the same settings. Then compare the RGB values at the exact same location in the image and you can see if there is a real transmission difference.

That's way better than trying to use the light meter as a measure.

JeffreyG wrote in post #17823728
To really find out, shoot two picks, one with lens and use the same settings. Then compare the RGB values at the exact same location in the image and you can see if there is a real transmission difference.

That's way better than trying to use the light meter as a measure.

To what end? In the first place, it is quite impossible to control the light. Even if it only takes seconds to change the lens, the light may change. You have no control over that. Even if it were possible to discover that one of the lenses has a slightly different transmissivity (pretty sure I just made that up), what do you do with that information? The only real solution is to test a large enough sample (30+) of 24-70 f/4L lenses to find out what the mean and SD are for transmissivity of these lenses. Then what? You still can't DO anything with that information. Statistics only tell you about the population (of lenses) in general. All of that work will provide no information about any specific lens coming off the production line. The only reasonable recourse is to shoot the lens you have. How all the others behave really is quite irrelevant to any specific shooter's outcome. Seems a bit like chasing unicorns.

Well, to me it sounded like the OP was curious. So the purpose of the test would be to see if there really is a detectable difference.

Light level variability is easily managed by testing on a clear day. Light levels during daytime hours, using only daylight, will not change shot to shot.

It's an easy test. I once tested all of the Canon lenses I owned to see what the transmission loss differences were. It was interesting.

Oh, and you can do the test inside with artificial lights too, but you need to use long shutter opening times to average the AC cycles.

Sorry for not replying earlier.
The next day I took back the lens in question and compared to the other lens in stock.
The lens in question not only read a third stop brighter, but the histogram and image showed as well.
The stock unit compared favorably to others in my Arsenal.
The new Stock unit is working just fine.