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FORUMS Photography Talk by Genre General Photography Talk
Thread started 13 Apr 2017 (Thursday) 12:33
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Understanding meter vs. exposure for your camera

 
Wilt
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Post has been last edited 13 days ago by Wilt. 6 edits done in total.
Apr 13, 2017 12:33 |  #1

In another forum, a discussion was started by someone trying to understand why four cameras (3 film, 1 digital) had meters which did not agree. He had exposed a roll of film, and had not yet posted scans of the resulting negatives from that camera. In participating in that discussion, I did a quick test of 4 cameras and a handheld reflected light meter, to see if they matched. The results:

  • OM-1: ISO1600 1/250 f/2.8
  • Minolta Spotmeter F: ISO1600 1/400 f/2.8
  • Canon 40D: ISO1600 1/400 f/2.8
  • Canon 5D: ISO1600 1/400 f/2.8
  • Canon 7DII: ISO1600 1/320 f/2.8


In looking at the histograms in Lightroom (with zero adjustment to exposure) I noted that


  1. the 7DII exposes so that histogram peaks exactly at the middle of the histogram, whereas
  2. the peaks on the 40D and 5D are about 0.33EV-0.5EV below midpoint


IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/Principles/7DII_zpsinazlx7e.jpg
7DII

IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/Principles/40D_zpsmo7mjtqh.jpg
40D

...so I conclude that my 7DII exposes more as I would expect the reflected light meter to behave...that is, putting the metered surface at the midpoint of the histogram. And if I compensate the 40D and 5D meters to peak at mid-histogram, their meters match the 7DII.

I knew my 5D and 40D matched each other for suggested exposure. I had not compared them to my recently acquired (used) 7DII. It was only in this comparison that I noted the different behavior in the recording by 5D/40D vs. where the 7DII placed its histogram peak. My initial reaction to this is "the 7DII seems to behave as I expect". I had not really pondered about why in LR3 my prior exposures with 5D and 40D all mostly seemed to need +0.33EV exposure adjustment in LR, it was simply 'a fact'...and now I understand why! In installing LR5 to support the 7DII, I had set up some presets for the 7DII starting with 'neutral' (no adjustment) values to various LR settings in LR5.7...and not I can see how this would better work for the 7DII than for the 4D/5D shots!

My point to this post is that prior to this comparison, I had not really noted the placement of the suggested exposure vs. what the camera recorded. It seems to be a very good exercise for others to point their cameras at a uniformly illuminated, uniformly colored wall, let the camera expose where the meter suggests, and then look at a histogram of the shot 'as shot' with no adjustments. You might well become 'enlightened' in doing so, as I was. All Canon cameras do not behave similarly in the 'as shot' results...I knew that from the past, I got verification of that once again.

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groundloop
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Post has been edited 13 days ago by groundloop.
Apr 13, 2017 12:59 |  #2

And to think that all along I'd been assuming that Canon engineers were smarter than the guy who wrote the laws of physics. :lol:

Thanks for this post, it's good information.




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TeamSpeed
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Post has been last edited 13 days ago by TeamSpeed. 2 edits done in total.
Apr 13, 2017 13:40 |  #3

It does seem Canon has been working out some exposure "kinks" or legacy behavior with newer bodies. The same rules of EC I had to use with older bodies don't apply to the newer ones, like the 7D2 and even now the 5D4.


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Tom ­ Reichner
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Apr 14, 2017 13:19 |  #4

Thanks for sharing these insights, Wilt.

I have always thought as meters as something that gives a recommendation, or an approximation, of what the exposure should be. I do not think that light meters should be used as an absolute standard whereby 'correct' exposure is determined.

This has popped up in a couple of other threads recently, where one member seems to be confusing metering problems with exposure problems. If people see meter readings as nothing more than suggestions that are to be experimented with and adjusted, then these misconceptions wouldn't be so common.

.


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MalVeauX
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Apr 14, 2017 15:18 |  #5

My older Canons, I generally have to use +1/3rd to +2/3rd EC to get exposure where I want it.

My 7D, the first time I did that with +1/3rd EC assuming it would need it to, over-exposed and blew highlights on whites. I have to run it at 0 EC, or even sometimes a hair negative!

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Wilt
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Wilt is an old fart who has extensive experience with many brands and many formats of cameras, and extensive lighting knowledge of both studio lighting and speedlights
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Post has been edited 11 days ago by Wilt.
Apr 14, 2017 15:35 |  #6

MalVeauX wrote in post #18327978 (external link)
My older Canons, I generally have to use +1/3rd to +2/3rd EC to get exposure where I want it.

My 7D, the first time I did that with +1/3rd EC assuming it would need it to, over-exposed and blew highlights on whites. I have to run it at 0 EC, or even sometimes a hair negative!

Very best,

Perhaps Canon has decided that simply building in a factor in the metering, to reduce the need for ETTR adjustment, was a wiser way to expose especially in view of user beefs in the past about pushed exposure noise compared to the Sony sensor?!


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Understanding meter vs. exposure for your camera
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