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Thread started 03 Jan 2015 (Saturday) 19:49
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Has anyone found some exposure issues with the 6D?

 
britinjapan
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Jan 06, 2015 07:32 |  #16

Ah, thanks, thats a good point, I had not thought of the 63 zone metering. What had me worried was less the slight differences mentioned above, but I did get a few shots that were clearly over or under exposed in extreme conditions - sudden shots taken soon after turning the camera on, and in extreme lighting - this Ive never had with Nikon - is this something that can happen, or does the camera always technically get exposure pretty much correct?


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Jan 06, 2015 10:11 |  #17

britinjapan wrote in post #17368661 (external link)
is this something that can happen, or does the camera always technically get exposure pretty much correct?

Yes.:!:


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Jan 06, 2015 14:09 |  #18

britinjapan wrote in post #17368661 (external link)
- is this something that can happen, or does the camera always technically get exposure pretty much correct?

No, the camera doesn't always get exposure correct, that isn't how the meter works. The meter aims to average all the tones to a mid-grey (typically between 14-18% grey) so depending on the tones in the scene, it may expose badly. If you have a lot of white in the scene, a snowy landscape for instance, then the camera will see all that white and try and make it grey, so underexpose significantly. If you want white snow you will need to add between 1 and 2 stops of exposure to the metered exposure. When I shoot, my actual exposure may be a couple of stops more or less than the camera suggests.

If you photograph a black card and a white card, at the metered settings, they will come out looking much the same, a mid grey tone. The black card will have been significantly overexposed and the white one significantly underexposed. The meter has done its job perfectly in both cases, it is up to the photographer to compensate for significant bright or dark areas that may affect the reading. If the scene has a good spread of tones, with few bright or dark areas, then the exposure will be pretty good as metered, but the camera will adjust the exposure up or down as you recompose, as you may be including more or less bright or dark areas. This is when manual is good, as you ascertain the correct exposure and set it, then all the fluctuations are ignored.

The meter is a tool to help you assess the exposure you need to give, it does not know whether your metered subject/scene is black, white or grey and will always expose to make it grey. If you are uncertain, then take a test shot and check the histogram, then adjust exposure accordingly.




  
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artyH
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Jan 06, 2015 18:09 |  #19

I thought that the camera routinely underexposed by 1/3 stop. Not so, but it does benefit from +1/3 stop exposure compensation at higher ISOs. Under fluourescent light, or even incandescent lighting and higher ISOs, +1/3 helps.
In bright light, adding 1/3 will often overexpose a bit.




  
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Jan 07, 2015 11:57 |  #20

I found my 7D vs. 5D III are about 2/3 a stop apart. Whereas I would normally leave the EC right at 0 to maybe +1/3 on my 7D I have to set it to 2/3 usually in order to get the same exposure. Why? I don't know but apparently its not an issue as a quick search turns up a billion threads on this.


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Jan 09, 2015 00:18 |  #21

I've found that my 6D will get confused a little bit, when there happens to be a very bright highlight in the frame. Some sunlight reflecting off a chrome car bumper for example. It will wildly underexpose. Like 1-1.5 stops at times. My EOS M doesn't exhibit the same behavior in similar conditions, but there's nothing wrong. They are both just different.




  
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britinjapan
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Post edited over 4 years ago by britinjapan. (5 edits in all)
     
Jan 09, 2015 19:23 |  #22

Thanks for all the great information. Ive tried to play around and recreate what prompted this thread. I set my camera in P mode and shot at the very center - that table leg. It was slightly darker at the middle, so the camera overexposes (or rather over exposes compared to the brighter next shot) - that makes sense. Its darker at the middle, so brings in more light. Changing the focus point to the brighter area on the left by an inch or so, brings the F stop to 2.5 from 1.6. Makes sense.

But if I change to MANUAL FOCUS and do the same thing, the almost exact exposure (in terms of look - by this I mean brightness of photograph) happens in both....why should changing to manual focus change this?

Here are my pics below:

All focus points were roughly at middle of pic, evaluative metering for all

1. Middle auto focus, 1/60, F1.6

IMAGE: https://farm8.staticflickr.com/7520/16216001876_20b9021d1e_b.jpg
IMAGE LINK: https://flic.kr/p/qGXf​pf  (external link) Middle auto focus 1/60 F1.6 (external link) by daizawaguy (external link), on Flickr

2. Slightly left auto focus (P setting) on brighter area, 1/60 F2.5

IMAGE: https://farm9.staticflickr.com/8619/16240040001_a3fa318298_b.jpg
IMAGE LINK: https://flic.kr/p/qK5s​6F  (external link) Left auto focus 1/60 F2.5 (external link) by daizawaguy (external link), on Flickr

3 and 4 are the same but at manual focus -(P mode)

3. F2.5

IMAGE: https://farm9.staticflickr.com/8597/15622025623_312fa80766_b.jpg
IMAGE LINK: https://flic.kr/p/pNsX​Xn  (external link) Manual focus left 1/60 F2.5 (external link) by daizawaguy (external link), on Flickr

4. F2.8

IMAGE: https://farm8.staticflickr.com/7489/16054510020_826b783833_b.jpg
IMAGE LINK: https://flic.kr/p/qsFy​uU  (external link) Manual middle focus 1/60 F2.5 (external link) by daizawaguy (external link), on Flickr

Does autofocus have an effect on exposure? If not, what happened above?

The exposure is different under autofocus and manual focus in exactly same camera settings and environment.

And if all were at 1/60, why would the exposures of F stops selected have been so different under manual and autofocus?

Putting it another way, the pink mat lying on the leg at the bottom of the photos clearly overexposed in the first. I understand this, as the point selected was darker in the first photo, but why would this difference not happen in manual focus?

Thanks

Canon 6D, 35mm F2 IS, 50mm F1.2L, 85mm 1.2L, 135mm F2L, 24-70 F4L, Tokyo, Japan

  
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britinjapan
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Jan 09, 2015 19:42 |  #23

Actually after posting the above I realized that I changed position a little, so Ive just tried setting aperture at say 2.8, and by not moving and just switching the button from manual to auto focus gives a significantly different picture. Im going to call Canon now...


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britinjapan
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Post edited over 4 years ago by britinjapan.
     
Jan 09, 2015 20:43 |  #24

When I first started this thread I swore there were exposure issues with my 6D. I listened to advice, but I didn't feel happy. The final acid test is that I leave my camera in the same mode, frozen on a table, and BY ONLY CHANGING THE AF/MF switch on the lens, the exposure changes. Ive spoken to Canon and they admit by this test (if the camera does not move), there has to be an issue. Down to the Canon center at Ginza, Tokyo this afternoon....

Stay tuned


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Jan 09, 2015 21:38 |  #25

britinjapan wrote in post #17374761 (external link)
When I first started this thread I swore there were exposure issues with my 6D. I listened to advice, but I didn't feel happy. The final acid test is that I leave my camera in the same mode, frozen on a table, and BY ONLY CHANGING THE AF/MF switch on the lens, the exposure changes. Ive spoken to Canon and they admit by this test (if the camera does not move), there has to be an issue. Down to the Canon center at Ginza, Tokyo this afternoon....

Stay tuned

Just found your Thread, You last post says it might be your camera, what lighting did you use?...............


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britinjapan
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Jan 10, 2015 06:59 |  #26

If by lighting you mean AWB, it was auto, in natural light. Just come back from Canon. They say there are no problems - the AF metering and MF metering is different, and will produce different settings. Im still not 100 pct happy - my Nikons never did this to this extreme. This last one is annoying. Ill try and post pics, but just by switching from AF to MF changed the exposure...what!!?? I mean you would think they would have this optimized no?


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Jan 10, 2015 08:59 |  #27

I can understand the difference between AF and MF. In evaluative mode it reads from the whole scene and uses algorithms to weight different areas and come up with (hopefully) an exposure that is roughly correct. One part of this is that it gives a significant weighting to the tones under the selected AF point, which is why exposure changes when you move that point from a dark tone to a lighter tone. If you switch to MF you are no longer using an AF point to focus so, I would presume, it doesn't weight the reading accordingly, this explains why it reacts differently in MF, you are using a different algorithm that doesn't weight to the AF point. It still reads from the whole scene though, and any camera movement will alter that scene and the meter reading may alter accordingly.

Your camera seems to be behaving as I would expect it to, the metering pattern changes when you switch to MF so the result will alter a little too. As I said earlier, the meter is a tool to help you judge exposure, it isn't there to always give perfect exposure, just get you close. It is up to the photographer to take appropriate meter readings, check the histogram if necessary, and decide on the appropriate exposure based on the subject and scene. You just need to understand your meter and take some responsibility for the exposure settings used.




  
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Post edited over 4 years ago by Wilt. (9 edits in all)
     
Jan 10, 2015 09:53 as a reply to  @ Sdiver2489's post |  #28

Sdiver2489 wrote:
I found my 7D vs. 5D III are about 2/3 a stop apart. Whereas I would normally leave the EC right at 0 to maybe +1/3 on my 7D I have to set it to 2/3 usually in order to get the same exposure. Why? I don't know but apparently its not an issue as a quick search turns up a billion threads on this.

Point both cameras at the same blank, uniformly illuminated wall, and verify that the indicated exposure is the same. That will prove to you that there is NOT a fundamental difference in meter calibration.

If there is a metering difference observed while in Evaluative mode, it is likely that any difference is caused by a difference in the distribution of the metering zones (different number of zones, different locations within the frame) so that the two cameras read the 'same scene' differently. And depending upon the programming of the meter by the engineers, perhaps one camera design gives a different weight to the biasing of the zones than the other design does. THAT is why you should start with comparing a blank, uniformly illuminated wall as I mentioned in the above paragraph.

Also, as mentioned by sandpiper, Evaluative biases metering to the AF zone(s) used yet still factors in all surrounding zones. So if the number of active AF zones is not identical (and refocusing with automatic AF zone selection will cause different AF zones to be used!), this can be another source of apparent 'metering difference'.

Lastly, unless all shots metered with Evaluative are taken with IDENTICAL framing -- using the camera set on a tripod from shot to shot -- any observations are inconclusive because the content of each of the metering zones in the frame are not necessarily the same...for example Frame 1 is not the same as Frame 2 is not the same as Frame 3 is not the same as Frame 4, in the above shots posted by britinjapan! So any change in exposure from shot to shot might simply be due 100% to framing!


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Jan 10, 2015 11:59 |  #29
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I didn't see a difference in britinjapan's last posting that could not be accounted for by a cloud drifting in front of the sun or someone walking by a window.


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britinjapan
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Jan 10, 2015 18:09 |  #30

Many thanks for everyones input. All very valuable. I understand there are no issues, and to mention again, all this is relative to my Nikon, where I have not noticed such differences in exposure. Sure, its a different system, different metering and algothythms, but have to give the points to Nikon on this one, and was expecting a bit more from my 6D. Im just a hobby photographist, but in some cases you can't go back and retake the photos nor have time to compensate for exposure, and this was really what prompted this thread. All very valuable inputs and what a great forum.


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