"Equivalence" demonstrated: Canon 5D and Panasonic GX1

Started Apr 27, 2013 | Discussions thread
Great Bustard Forum Pro • Posts: 42,264
Defining "Equivalent"

Amin Sabet wrote:

I recently took all my cameras and shot some photos of the same subject from the same distance with them.

These were my settings:

Leica M9 and 35mm lens at f/8, 1/60s, ISO 6400 (2500 pushed 1.3 stops in Lightroom)

Sony NEX-5N and 24mm lens at f/3.2, 1/60s, ISO 1000

Fuji X-E1 and 24mm lens at f/5, 1/60s, ISO 2500

Olympus E-PM2 and 17mm lens at f/4, 1/60s, ISO 1600

I resized all of those to the same diagonal pixel dimension and showed them to a bunch of family and friends, asking the simple question "Which of these images look equivalent to you?"  When pressed to explain what I meant by equivalent, I offered the guidance "Similar in visual properties".

Good test.

According to Joe's proposed definition of "equivalent images", the Leica, Fuji, and Olympus images were equivalent, and the Sony not equivalent.  Indeed, I could tell that the Sony image had less DOF than the others.  Yet everyone picked the Sony, Fuji, and Oly shots as equivalent, noting that the obvious difference in visual properties was how noisy the Leica image looked.  The second most common observation had to do with slight differences in color rendition.  No one commented on the DOF differences, including my wife who often complains about a photo being blurry when I use a narrow DOF.

So, is it fair to say that your conclusion is that noise and color are more significant than DOF?  I would certainly agree, depending on the differences between noise, color, and DOF.  Same goes with other elements of IQ, such as detail, bokeh, moire, etc.,

To some people, a 35/1.4 on a Leica M9 doesn't produce an image equivalent to one made with a 35/1.4 on a D800.  To this guy, a Canon 35/1.4 on a 5D III doesn't produce an image equivalent to one made with a Sigma 35/1.4 on a D800.

Of course, "equivalent" does not mean "equal".

Arguing about what is equivalent is like arguing about what is compact.  There is no accepted definition other than the common use as pertains to focal length equivalents.  There is a proposed definition of "equivalent image" but not an accepted one.

Equivalent photos, as I define them, are photos with the same perspective, framing, DOF, shutter speed, and display size.  They are independent of the technology used to capture the photo.  Other elements of IQ, such as detail, noise, dynamic range, color, etc., all may matter more than any of the five parameters of Equivalence, depending on the scene in question.

What I find interesting is that no one would object to Equivalence being defined as "same AOV and exposure".  I dare say, you'd never have bothered with the test if Equivalence had been defined in such a manner.

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