Rethinking 4/3 Depth Of Field

Started Apr 11, 2013 | Discussions thread
Great Bustard Forum Pro • Posts: 40,876
It really isn't.

Rriley wrote:

Great Bustard wrote:

Alumna Gorp wrote:

Great Bustard wrote:

Alumna Gorp wrote:

Have a read at this.

...and made a few notes on some of his opinions:

No bleeding you again

That's right -- I had forgotten we had crossed paths before:

By the way, here's a current case-in-point as to why an understanding of Equivalence is useful for many:

Seems that f/2.8 isn't f/2.8 after all, eh? 

at some point some lenses will
where DoF is settled to be satisfactory as opposed to absolute, and 2.8 (in this case) is the minimum aperture a lens offers, 2.8 does indeed = 2.8

No, it's just the best that it can do.

astro is a good example, where stars are so far away that f/2.8 lens can be set to infinity and no closer DoF need be considered. And as it happens there is a shutter speed limit of 20 seconds before stars becomes lines or streaks.

Exposure is dominant in such a calculation, and DoF is deemed achievable and satisfactory

But even when DOF doesn't matter (either because we don't care, or the whole of the scene is well within the DOF even at wide apertures), it's still not about exposure, but about the total amount of light collected:

Total Light Collected = Exposure x Effective Sensor Area x QE

So, exposure is relevant only inasmuch as it is a component of the total light collected.

If for some reason greater DoF is required (including part of a landscape) smaller sensors are likely to benefit from this restraint having inherently greater DoF, for a given shutter speed and limited widest aperture (f/2.8).

Smaller sensor systems have not "inherently greater DOF" except when we are in apertures deep into diffraction territory (past f/22 equivalent on FF).  For example, if someone is shooting f/8 on mFT for DOF reasons, then the FF photographer would simply shoot f/16.

On the other hand, if the mFT photographer was shooting f/22, the FF photographer cannot shoot f/44 (f/45), so the mFT system would have a DOF advantage.  That said, if "high IQ" is important, then both the mFT and FF photographers would make use of focus stacking, which, incidentally, was just discussed in a nice article here on DPR:

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