Does f1.4=f2.8 in reality?

Started Jun 27, 2010 | Discussions thread
boggis the cat
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Re: Not equal to -- equivalent to...
In reply to g r e e n p e a, Jun 30, 2010

g r e e n p e a wrote:

...where "equivalent to" means for the same:

  • perspective

  • framing

  • DOF

  • shutter speed

  • display dimensions

Although there is a slight niggle due to the difference in aspect ratio between 4/3 and 135.

There is another "slight niggle" in that you must adjust the ISO setting to maintain the exposure after adjusting the f-number to get an equivalent DOF.

For the benefit of the OP: some people use "equivalence" as a short-hand for "an equivalent photo" -- the same elements and framing at the same distance with the same apparent depth of field.

Nevertheless, f/2 is not equivalent to anything other than f/2 unless you explain what you are using as a reference -- in this case, the reference is depth of field. This is why we say 4/3 has twice the depth of field of 135* -- your f/1.4 lens on a 4/3 body will yield twice the depth of field as on a 135 body (such as a 35 mm film camera).

[* "135" was the designation of the film cartridge developed by Kodak that was used in 35 mm cameras. I prefer this term to "35 mm" or "full frame". It has no units that may cause confusion, and systems such as 4/3 are "full frame" as well.]

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