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Archive 2014 · Should the 16-35/4 IS underexpose like this?

  
 
memoria
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p.1 #1 · p.1 #1 · Should the 16-35/4 IS underexpose like this?


So UPS delivered the 16-35/4 friday and I've been testing it a bit during the weekend. The lens is sharp as hell and contrasty as expected - however I noticed that it appeared a bit "dark and muddy" compared to my other L's. I thought it might just be the light but then I ran quick test and it confirmed that the lens is indeed darker, almost 1 stop. If not more in certain scenarios.

The attached images might show what I mean. I used the 40/2.8 as a reference this time (it behaves like my other L's in terms of brightness). I stopped the 16-35 down more in order to get rid of vignetting

Notice how the 16-35 is almost 1 stop underexposed?

Is it a lemon? Am I missing something?

40/2.8
http://s27.postimg.org/y85397fxv/40mm.jpg

16-35/4
http://s28.postimg.org/vfdwm8j7x/16_35.jpg

Edited on Sep 29, 2014 at 08:54 AM · View previous versions



Sep 29, 2014 at 08:42 AM
Ian.Dobinson
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p.1 #2 · p.1 #2 · Should the 16-35/4 IS underexpose like this?


probably should have all the same settings for both . but it wouldnt surprise me if the T stop of the 16-35/4 was not just 1 stop slower than the T stop of the 40/2.8


Sep 29, 2014 at 08:51 AM
ccho
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p.1 #3 · p.1 #3 · Should the 16-35/4 IS underexpose like this?


Ian's explanation sounds plausible -- in case you're wondering what a T-stop is, read this thread:

http://photo.stackexchange.com/questions/21940/what-is-t-number-t-stop



Sep 29, 2014 at 08:58 AM
memoria
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p.1 #4 · p.1 #4 · Should the 16-35/4 IS underexpose like this?


I re-ran the test, all manual with same settings and the difference is smaller, perhaps 1/3 of a stop. So it seems the autoexposure is being tricked by the T-stop forcing an unwanted underexposure.

Note to Canon: please include exposure micro adjustment on lenses as well (similar to the AF adjustment).

It's weird though...why is the lens so different? I own (or have owned) the 16-35/2.8 II, 24-70 2.8L, 35L, 40/2.8, 50L, 85L, 100L Macro, 135L, 70-200L IS - the have NEVER ever been like this on autoexposure. If I need to dial in +1 everytime I put the 16-35 on, it's going back to the store. The L series should be somewhat consistent

Edited on Sep 29, 2014 at 09:14 AM · View previous versions



Sep 29, 2014 at 09:06 AM
gse53
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p.1 #5 · p.1 #5 · Should the 16-35/4 IS underexpose like this?


Very interesting topic.

Just for yucks, I checked DXOmark T-stop scores for both lenses. I always wondered the significance of those scores.

40mm STM = 2.8T

16-35mm F4 = 4.5T

Ian, I think you nailed the reason.

Another thing to consider when buying a lens.

Note to Canon: please include exposure micro adjustment on lenses as well (similar to the AF adjustment).

Isn't that what the +/-ev setting is?



Sep 29, 2014 at 09:13 AM
memoria
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p.1 #6 · p.1 #6 · Should the 16-35/4 IS underexpose like this?


gse53 wrote:
Isn't that what the +/-ev setting is?


Not quite...that setting is global for the light meter. If a particular lens for some reason forces the camera to underexpose, I would like to fine-tune that specific lens/body combination.



Sep 29, 2014 at 09:56 AM
kezeka
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p.1 #7 · p.1 #7 · Should the 16-35/4 IS underexpose like this?


It's unusual that the 40/2.8 has the same f number as t number. Usually the f number is 1/3 to 1/2 stop slower. That would explain the difference in metering. For what it's worth, I have to meter to he right for all of my lenses.


Sep 29, 2014 at 10:40 AM
Photonadave
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p.1 #8 · p.1 #8 · Should the 16-35/4 IS underexpose like this?


memoria wrote:
I re-ran the test, all manual with same settings and the difference is smaller, perhaps 1/3 of a stop. So it seems the autoexposure is being tricked by the T-stop forcing an unwanted underexposure.

Note to Canon: please include exposure micro adjustment on lenses as well (similar to the AF adjustment).

It's weird though...why is the lens so different? I own (or have owned) the 16-35/2.8 II, 24-70 2.8L, 35L, 40/2.8, 50L, 85L, 100L Macro, 135L, 70-200L IS - the have NEVER ever been like this on autoexposure. If I need to dial in +1 everytime I put the 16-35 on,
...Show more

Your manual test makes sense to me.

In the case of TTL metering the camera's auto exposure metering mode should normally adjust for the T-stop variation between lenses. Less light making it to the metering sensors in the camera due to T-stop = camera automatically selecting a wider aperture letting more light in, thus compensating for T-stop, and then relaying that command to the lens. I suspect that the aperture is mechanically out of adjustment stopping down too much on that particular lens.

Thus:

+1 on the your request for Canon adding an exposure micro adjustment feature. I'm thinking this feature would reside in camera like AF Micro Adjustment which I think is probably what you meant. ("for" instead of "on").



Sep 29, 2014 at 11:42 AM
RobDickinson
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p.1 #9 · p.1 #9 · Should the 16-35/4 IS underexpose like this?


The camera meters the light once it is through the lens, should compensate in any auto mode


Sep 29, 2014 at 12:39 PM
willis
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p.1 #10 · p.1 #10 · Should the 16-35/4 IS underexpose like this?


In the example shown I think it's more likley that the multi pattern metering is just interpreting the scene differently. The framing doesnt match exactly and the sky is close to 50% of the scene but probably not easily recongised as sky by the metering programme because the "horizon" is so irregular. It's likley that in the first the meter has exposed more for the sky and in the second for the buildings. Have you tried it with a uniform subject or spot metering?
I dont understand how the T stop would be relevant for AE modes. The meter reads transmitted light not nominal aperture.



Sep 29, 2014 at 12:55 PM
gse53
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p.1 #11 · p.1 #11 · Should the 16-35/4 IS underexpose like this?


The framing doesn't match exactly

Very good point. The test should be on a tripod showing the exact same composition. The eval metering might be making adjustments based on the field of view. That being said, look closely at the two photos. The front wall on the first is way too hot. The second seems to have a better exposure. Just my 2 pennies.

I would test more before sending it back.

Then again, you cannot get the same photo on a tripod as the Canon does not go to 40mm. Oh well.



Sep 29, 2014 at 01:12 PM
PaulB
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p.1 #12 · p.1 #12 · Should the 16-35/4 IS underexpose like this?


It could be difficult to get the 16-35/4 to compose the scene exactly as the 40/2.8............
Greater area of sky and light walls on 35mm are making the difference to the metering.



Sep 29, 2014 at 01:25 PM
unclechuck
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p.1 #13 · p.1 #13 · Should the 16-35/4 IS underexpose like this?


Folks

I have learned more about photography in 4 1/2 years on FM than in the 40 before: this T stop is ALL new to me.

Without fully understanding T here's what I would have done:

I'd set up well lit sky shot, nothing but sky as this isn't about focus.

With the camera on a tripod at ISO100 I'd mount the 40mm and shoot at f/4, infinity

The switch to 16-35 f/4 L infinity.

Would those two images give a baseline of the difference?

Charles



Sep 29, 2014 at 01:44 PM
Glenn NK
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p.1 #14 · p.1 #14 · Should the 16-35/4 IS underexpose like this?


PaulB wrote:
It could be difficult to get the 16-35/4 to compose the scene exactly as the 40/2.8............
Greater area of sky and light walls on 35mm are making the difference to the metering.


This stuff is a bit beyond my comprehension, but it was brought up on another forum and explained by an astrophysicist (who is also a photographer):

http://en.wikipedia.org/wiki/Etendue



Sep 29, 2014 at 02:59 PM
Photonadave
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p.1 #15 · p.1 #15 · Should the 16-35/4 IS underexpose like this?


willis wrote:
In the example shown I think it's more likley that the multi pattern metering is just interpreting the scene differently. The framing doesnt match exactly and the sky is close to 50% of the scene but probably not easily recongised as sky by the metering programme because the "horizon" is so irregular. It's likley that in the first the meter has exposed more for the sky and in the second for the buildings. Have you tried it with a uniform subject or spot metering?
I dont understand how the T stop would be relevant for AE modes. The meter reads transmitted
...Show more

Good point about the framing mismatch effect on metering!

The example shot taken with the new lens data says that it received 1/3rd stop less exposure by the camera settings compared to the 40mm lens test shot. That's caused by 1/3 stop more exposure by 1/1600 shutter speed - 2/3 stop less by smaller f/6.3 aperture= 1/3 stop total less exposure probably due to what you say. When I look at the comparisons of all shots at the bottom it looks like more than 1/3rd stop difference to me on my calibrated editing monitor.


To OP memoria:

I suggest that you re-take the test shots with the various lenses while the camera is locked down on a tripod (as suggested by another poster) without moving anything. Set the camera in AV auto exposure mode with all lenses set at the same aperture. To eliminate influences from the small focal length variation between the lenses and also from varying subject detail use an evenly lit blank solid light color wall or the same area of clear blank sky, not anywhere near the sun and avoiding morning or evening time when the light is changing rapidly.

Edited on Sep 29, 2014 at 11:14 PM · View previous versions



Sep 29, 2014 at 05:20 PM
kevindar
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p.1 #16 · p.1 #16 · Should the 16-35/4 IS underexpose like this?


OK Gang.
So, this was shot in Av mode. Metering and comp here is not an issue desipite being shot in av mode. both are identical exposures, as far as the camera is concerned. both are iso 400, one is 1/1600 sec, f 6.3, and one is 1/2000 f5 (1/3 stop difference in apertaure compensated by 1/3 stop difference in shutter speed).
Now the difference in framing has probably led to camera choosing the same exposure in the two scenes. if the scenes were framed identically, the camera would have chosen 1/3 to 1/2 exposure longer for the 16-35 f4 lens, b/c of the t value of the lens (not that the camera knows about it, just think of it as having a .5 stop nd in front of the lens.

So, the t stop, does not lead to darker exposures, but longer exposure times, will all else being the same, compared to a lens with a lower t stop.



Sep 29, 2014 at 05:45 PM
timbop
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p.1 #17 · p.1 #17 · Should the 16-35/4 IS underexpose like this?


RobDickinson wrote:
The camera meters the light once it is through the lens, should compensate in any auto mode


exactly



Sep 29, 2014 at 07:44 PM
Photonadave
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p.1 #18 · p.1 #18 · Should the 16-35/4 IS underexpose like this?


RobDickinson wrote:
The camera meters the light once it is through the lens, should compensate in any auto mode


---------------------------------------------

timbop wrote:
exactly


Yes! All auto exposure modes! My example was for TV mode, one of several auto modes depending on camera model.



Sep 29, 2014 at 09:17 PM
kezeka
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p.1 #19 · p.1 #19 · Should the 16-35/4 IS underexpose like this?


kevindar wrote:
OK Gang.
So, this was shot in Av mode. Metering and comp here is not an issue desipite being shot in av mode. both are identical exposures, as far as the camera is concerned. both are iso 400, one is 1/1600 sec, f 6.3, and one is 1/2000 f5 (1/3 stop difference in apertaure compensated by 1/3 stop difference in shutter speed).
Now the difference in framing has probably led to camera choosing the same exposure in the two scenes. if the scenes were framed identically, the camera would have chosen 1/3 to 1/2 exposure longer for the 16-35 f4 lens,
...Show more

Metering is ALWAYS an issue when this test is not standardized. Canon evaluative metering does whatever the hell it pleases and gets it somewhat right most of the time, sometimes. A real test would be to show us the actual photos taken in full manual at the same settings with both lenses.

The actual answer is to just preset your metering to expose to the right.



Sep 29, 2014 at 09:23 PM
kevindar
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p.1 #20 · p.1 #20 · Should the 16-35/4 IS underexpose like this?


kezeka, read my post again. the two images should have identical luminosity in overlapped area, b/c they appear to have identical exposure in the exif. in reality, they dont. its b/c the f6.3 of the zoom lens, is really not f 6.3.
to test for true t value, you should shoot in manual mode, with identical settings. sure, having identical framing is nice, but this is not about camera metering, its about the true t stop of the lens.



Sep 29, 2014 at 10:39 PM
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