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Recently I've asked about the difference between two lenses on open apertures: Why do two lenses with the same F-number give different amount of light?

We realized that DSLRs gain the real ISO without letting us to know, when we shooting on open apertures. Matt Grum has linked to DxO article: http://www.dxomark.com/Reviews/F-stop-blues

And here's the chart from this article showing how many stops different cameras lose when we take pictures on f/1.2:

ΔEV at f/1.2 function of pixel pitch

We can see here, for example, that classic Canon 5D has a better performance on open apertures than Canon 5D Mark II.

In that question, we also realized that the camera's ISO gain function doesn't work when we use a manual lens (without electric contacts with camera) or when we use a common lens and turn it around itself (so the camera loses contacts with the lens and doesn't know what aperture set on the lens). If the camera doesn't know anything about the aperture, it doesn't gain ISO at all, even if we really open the aperture (for example, f/1.2 or f/1.4) on our manual lens.

My wish is to verify, is that real that these two cameras has difference performance on open apertures.

Therefore I want to ask somebody who has both classic 5D and 5D Mark II and manual fast lens to make the real test of these two cameras. You need to take two shots using the same lens, shutter speed, aperture (f/1.4, f/1.2 or faster), ISO, focusing distance and distance to the object, but different cameras (5D and 5D Mark II). It also would be great if you has a tripod.

If you don't have fast manual lens, you can use a common fast lens, but you need to turn the lens slightly around itself in order to take away the electric contacts from the place where they should be.

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    While I only have the 5D Mark iii, I would ask about what you are hoping to gain from the information. The EV decrease is smaller on the 5D, but the pixel pitch is also much larger. This is because of the difference in resolution of the sensors which also means that the light wells are wider. This is probably why it has such a significant advantage, but it also means that there is a significant disadvantage in terms of resolution. – AJ Henderson Oct 25 '13 at 17:22
  • I know that this difference is a result of a difference in pixel pitch. What I want is an obvious comparison, when we can see this difference by ourselves. – Sunny Reborn Pony Oct 25 '13 at 19:31
  • What is the best way to title this question? What words should I use? – Sunny Reborn Pony Oct 25 '13 at 19:31
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I only have odd numbered 5Ds, but the pixel pitch is very similar between the 5DmkII and 5D mkIII so the results ought to hold up.

Here's the same scene shot using a tripod under the same lighting, 1/8s exposure ISO 100, f/1.2 (using the Canon 85L). RAW, converted with ACR with the same settings (everything on zero with a linear tonecurve).

I shot pairs of images with each camera, the first with the lens mounted normally and the second with the lens twisted slightly to break contact and hide the aperture info from the camera body:

http://www.mattgrum.com/photo_se/f1_2/5D.gif

5D


http://www.mattgrum.com/photo_se/f1_2/5D_mkIII.gif

5D mkIII


The luminance values for the lightest grey patch with and without aperture information were 76 : 73 for the 5D and 75 : 70 for the 5D mkIII

As expected the difference in exposure is greatest with the 5DmkIII due to it's smaller pixels (the markIII loses more light with ultra-fast lenses).

However the difference between the actual and camera-adjusted images seems less than the 0.4EV and 0.65EV suggested by the DXO chart. So either the loses aren't as bad as DXO states or the camera is not adjusting the images by as much as it should do. Unfortunately I don't have the necessary equipment to say for sure.

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I recently had a fairly lengthy debate about the whole issue of pixel pitch, ISO performance, and aperture on the Canon Rumors forums. Suffice it to say, while I did not necessarily change my opinion (my angle on the debate was different than that of my opponent), I found the following article on "Equivalence" to be quite enlightening, and expanded my opinion on the subject:

Equivalence, by Joseph James

One of the most important quotes from this article would be from the MYTHS AND COMMON MISUNDERSTANDINGS section:

The reason that the total amount of light falling on the sensor, as opposed to the density of light falling on the sensor (exposure), is the relevant measure is because the total amount of light falling on the sensor, combined with the sensor efficiency, determines the amount of noise and DR (dynamic range) of the photo.

For a given scene, perspective (subject-camera distance), framing (AOV), and shutter speed, both the DOF and the total amount of light falling on the sensor are determined by the diameter of the aperture. For example, 80mm on FF, 50mm on 1.6x, and 40mm on 4/3 will have the same AOV (40mm x 2 = 50mm x 1.6 = 80mm). Likewise, 80mm f/4, 50mm f/2.5, and 40mm f/2 will have the same aperture diameter (80mm / 4 = 50mm / 2.5 = 40mm / 2 = 20mm). Thus, if we took a pic of the same scene from the same position with those settings, all three systems would produce a photo with the same perspective, framing, DOF, and put the same total amount of light on the sensor, which would result in the same total noise for equally efficient sensors (the role of the ISO in all this is simply to adjust the brightness of the LCD playback and/or OOC jpg).

Thus, settings that have the same AOV and aperture diameter are called "Equivalent" since they result in Equivalent photos. Hence, saying f/2 on one format is the same as f/2 on another format is just like saying that 50mm on one format is the same as 50mm on another format.

We all know that a 50mm on FF is NOT the same as a 50mm on APS-C...hence the importance of understanding equivalence. This applies to sensors of the same size but different pixel pitch as well, since it effectively becomes a non-factor when the total sensor area is taken into account (only sensor efficiency, which boils down to read noise, really matters.)

This is probably one of the most informative articles on what REALLY MATTERS when it comes to exposure in photography. There are a lot of debates about pixel pitch, ISO and true sensor sensitivity, etc. But when you boil it all down, equivalence is really what matters, and everything else is just fluff. Before you comment, it is important that you read everything in the article at least up to the noise section, and preferably read the ENTIRE article (yes, I know its very long, but it once you finish it, you'll probably find you don't need to ask this kind of question.)

  • I'm very familiar with the Joseph James equivalence essay, however the pixel pitch does matter even with sensors of the same size since it affects the angular efficiency which is important with very fast lenses. The total light falling into the sensor might be the same but the total light reaching the photosensitive silicon at the very bottom of the sensor is different, and the experimental results back this up. – Matt Grum Oct 25 '13 at 23:44
  • @Matt: Sure, I don't dispute that. However there are a number of technologies these days that affect that, and the differences with microlenses, double-layer microlenses, offset microlenses, color spitting, etc. are all rather minor in the grand scheme of things. Angular efficiency ultimately boils down to a factor of "sensor efficiency", which Joseph covers in this article. The point of linking the article is to demonstrate that in the context of any given sensor size, differences in pixel pitch and the impact on exposure don't matter as much as the total amount of light gathered. – jrista Oct 26 '13 at 21:07
  • Both the 5D III and 5DC are going to gather roughly the same amount of total light for any given lens and aperture, even if per-pixel exposure and ISO might differ by a small amount (less than a third of a stop...differences in lens transmission can vary buy that much.) In the end, the 5D III and 5D C sensors are both going to take quality photos, and the differences don't matter unless you are enlarging to gargantuan proportions. (There are other differences that make the 5D III a vastly superior camera, but those are external to the sensor.) – jrista Oct 26 '13 at 21:09

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