A few words on Equivalence and comparing systems

Started Apr 2, 2013 | Discussions thread
Great Bustard
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Re: On "f/2.8 = f/2.8" and "being anal"
In reply to Alumna Gorp, Apr 2, 2013

Alumna Gorp wrote:

Great Bustard wrote:

Alumna Gorp wrote:

"in other words, simply because 35-100mm f/2.8 on mFT is equivalent to 70-200mm f/5.6 on FF"

Jeez man, not again, a 2.8`s, a 2.8 unless your being anal.

Saying "f/2.8 = f/2.8" is no more or less true than saying "50mm = 50mm".  In other words, it makes no more sense to compare f/2.8 on mFT to f/2.8 on FF than it does to compare 50mm on mFT to 50mm on FF.

Nope a 2.8 is a 2.8, any light meter will tell you so

50mm = 50mm -- any lens will tell you so.

But your going on about DOF, a totaly different ball game.

Not just DOF, but the total amount of light projected on the sensor for a given shutter speed.  For example, 50mm f/2.8 1/100 projects four times as much light on the sensor as 25mm f/2.8 1/100 on mFT (resulting in half the noise for equally efficient sensors), or, alternatively, 50mm f/5.6 1/100 on FF projects the same total amount of light on the sensor as 25mm f/2.8 1/100 on mFT (which will result in the same noise for equally efficient sensors).

So, instead of quoting numbers without knowing what these numbers have to do with the visual properties of the final photo, you might wish to instead consider how these numbers relate to the visual properties of the final photo.

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