"Equivalence" demonstrated: Canon 5D and Panasonic GX1

Started Apr 27, 2013 | Discussions thread
boggis the cat Veteran Member • Posts: 6,329
'Equivalent' can mean many different things

Great Bustard wrote:

They're all quantative.  We can quantify perspective (subject-camera distance).  We can quantify framing (width and height of the scene on the focal plane).  We can quantify DOF (total distance front and back of the focal plane that is within critical focus).  In other words, they are all quantative just like shutter speed and display size.

Here, let me ask you a question:  would anyone disagree that 25mm f/2.8 1/100 ISO 400 with the 14=54 / 2.8 on an Olympus E1 is equivalent to the same settings with the 12-35 / 2.8 on an Olympus EM5?

I would disagree.  The E-1 produces a very different photograph to the E-M5, even when using the same lens on both.

So I would say that such photos were "of the same subject" or even "the same photo, using two different cameras".  The point would actually be that they are not equivalent.  If they were, I could have saved a lot of money upgrading bodies to obtain a technically better photograph.

(Edit: OTOH, the E-1 may produce as perfectly good a result as the E-M5 for a given situation and end use.  It may be 'good enough'.)

I'm thinking no one would say they are not "equivalent", despite the fact that the noise, detail, dynamic range, etc., would all be quite different.

You have a very narrow idea of what 'equivalent' should mean -- or rather 'equivalent photographs', where you use 'equivalent' as a short-hand for that concept.

Because of this narrow idea, you then have trouble with the concept that a 50 mm f/2 lens on FT is equivalent to 100 mm f/2 on 135.  In this case, we'd be considering equivalent focal length in 135 terms: 100 mm EFL (where "EFL" is an 'industry standard' terminology using the 135 film system as a basis for comparison).

It is not in fact necessary to 'correct' such a statement to "50 mm f/2 lens on FT is equivalent to 100 mm f/4 on 135" if you are discussing EFL.  The advantage that a larger sensor has (or may have) is always 'present', and may be pointed out if relevant.

Thus, I see no reason not to use the word "equivalent" to describe photos that have the same perspective, framing, DOF, shutter speed, and display size even when other elements of IQ are not necessarily the same.

Once again, I suggest that you use 'equivalent photographs' as a clearer indication of what you are referring to in preference to your short-form usage of 'equivalent' or 'equivalence'.  This prevents confusion when, for example, you jump into a discussion comparing lenses where other 'equivalents' may already being discussed and essentially try to narrowly redefine the word 'equivalent'.  It is irrelevant to the point that you are making (about total light capture and sensor noise level) and may lead to unnecessary confusion and argument.

'Equivalent' does not have the narrow meaning that you may prefer it to have.

 boggis the cat's gear list:boggis the cat's gear list
Olympus E-5 Olympus E-M1 Olympus Zuiko Digital ED 12-60mm 1:2.8-4.0 SWD Olympus Zuiko Digital ED 50-200mm 1:2.8-3.5 SWD Olympus 12-40mm F2.8 +7 more
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