The Recent F/stop Controversy

Started 1 month ago | Discussions thread
fferreres Senior Member • Posts: 1,587
Re: The Recent F/stop Controversy

Great Bustard wrote:

Indeed. However, an important lesson that Equivalence explains is that, for a given DOF and exposure time, the same total amount of light is projected on the sensor for *all* systems.

Correct (except the part "important lesson")

So, for a larger format to have a light gathering advantage over a smaller format, the larger format *must* use a more narrow DOF or a longer exposure time. That's worth knowing, methinks, even if one is otherwise uninterested in other Equivalence related topics.

And the "important lesson" ends in embarrassment, methinks, because it could actually very well be the case that the larger format may not need to do ANYTHING to have a light gathering advantage, because it may spread that light over a larger sensor, and the smaller format may need to increase the DOF or reduce exposure time to actually not clip all the highlights.

So no. It may need to do it. Or it may not need to do it....

Equivalently, really just depends.

** Epilogue **

Equivalence is to Numbers, as Analogy is to Concepts. It works only across a subset of the argument, and thus cannot be stated as Equal. Because it's not Equal, it's just an "Accountants" approach photography, dealing with equivalences that only work " in some ways and fail in some others.

Even things that you can consider result in the same thing, produce results that are NOT equivalent, regardless of your light accounting best practices. A 50mm f1.4 lens will never be a 25mm f1.4. Actually, no lens half the FL and same aperture is same. It cannot be equivalent, because each will have different optical characteristics. But for the Equivalence scientist they are all and indistinguishable ---> depending on what sensor you put behind.

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