"Equivalence" demonstrated: Canon 5D and Panasonic GX1

Started Apr 27, 2013 | Discussions thread
Great Bustard Forum Pro • Posts: 39,716
Here you go:

walkaround wrote:

Great Bustard wrote:

All you've demonstrated is that the GX1 has a more efficient sensor than the 5D, and that the predictions of Equilvance are exactly as stated.

So, that's an epic fail on your part.

The problem mr bustard is that you pick a definition of "equivalent" for two photographs that incredibly does not include exposure which is the basis of photography. From your website essay:

"Equivalent photos are photos of a given scene that share the following five parameters:

•  Perspective •  Framing •  DOF •  Shutter Speed •  Display Dimensions

Equivalent images on different formats, by definition, will not have the same exposure, and this is the source of most all resistance to the concept."

Exactly correct.  This is because:


In terms of IQ, the total light is the relevant measure, because both the noise and DR (dynamic range) of a photo are a function of the total amount of light that falls on the sensor (along with the sensor efficiency, all discussed, in detail, in the next section).

You should have wrote "by my definition", because I can't imagine there are very many people outside of this forum who believe that two photos two stops apart in exposure are in any way "equivalent", and you choosing to define it such just makes your definition irrelevant.

The resistance to your "concept" that you note is because it doesn't make sense. I can write an article on cooking and state that the definition of good cooking does not include "taste", but who cares and who would want to read it?

Now this is all ok if you're just chatting with mom in the basement, but we now have threads here where people say "I'm going to buy the new Voigtlander f/0.95 because having an f/2.0 lens will still be fast enough for me." Sheesh.

I wouldn't expect someone with 15000 posts to ever say "you're right", but hopefully others will see that they can go out and buy that f0.95 lens and it will in fact still be an f0.95 lens when they get home and stick it on their m4/3 camera.

And if you are now claiming that the GX1 sensor is 4x more efficient than the 5D, please post a source for that information because I think it's nonsense.

I have an answer for all that, too:


Of course, sensors are not equally efficient (although often, but not always, close for a given generation).  However, that doesn't stop us from saying that a 50 / 1.4 on a Canon 5D is not equivalent to a 50 / 1.4 on a Nikon D600.  Nor are lenses equally sharp, have the same color, bokeh, or flare characteristics, but this does not stop us from saying that the Canon 50 / 1.4 is equivalent to the Nikon 50 / 1.4G which is equivalent to the Sigma 50 / 1.4.

Indeed, according to Webster's, the primary definition of "equivalent" is:

1: equal in force, amount, or value

So, "equivalent images" have equal perspective, equal framing, equal DOF ,equal shutter speeds, and equal display dimensions, although other characteristics, such as noise, detail, etc., may be equal under specific conditions.  The second and third definitions of "equivalent" also fits:

2a:  like in signification or import3:    corresponding or virtually identical especially in effect or function




Equivalent images on different formats, by definition, will not have the same exposure, and this is the source of most all resistance to the concept.  Many feel that exposure has been usurped with DOF, but this reflects not only a lack of understanding of what exposure actually is, but how much of a role DOF plays in a photo, even if DOF, per se, is not a consideration.  While the artistic value of DOF is subjective, the fact is that both the total light and the DOF are functions of the aperture diameter.  Larger aperture diameters admit more light, but they also introduce more aberrations from the lens.  Thus, DOF, noise, and sharpness are all intrinsically related through the aperture of the lens.

In short, you would be well served to understand what Equivalence says before posting threads like this one.

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