Rethinking 4/3 Depth Of Field

Started Apr 11, 2013 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: Lovely pix and excellent presentation of your argument

Great Bustard wrote:

Anders W wrote:

Great Bustard wrote:

Anders W wrote:

Great Bustard wrote:

Anders W wrote:

Great Bustard wrote:

There are quite a few fast primes for FF that aren't particularly expensive:  35 / 2, 50 / 1.8, 50 / 1.4, 85 / 1.8, 100 / 2.

On the other hand, many of those that aren't particularly expensive aren't very good wide open and thereabout. I am not saying that exceptions do not exist, but they are hardly frequent. Most of the fast Oly & Pany MFT primes, by contrast, do very well already from the get-go, and at least some of them are quite affordable too (20/1.7, 45/1.8).

Well, I guess it depends on what you mean by "aren't very good wide open" -- I found the 50 / 1.4:

85 / 1.8:

and 100 / 2:

more than "good enough", although that's not to say that I would not be against paying more for better still.  Indeed, I paid a lot more for the 50 / 1.2L:

but I have to wonder how many, if anyone, appreciates the difference.

My definition of "not very good" is something like "significantly worse than peak performance".

Hmm.  My definition of "not very good" would be more like "doesn't deliver desired results".

I am not sure the two definitions are very different.

I'm thinking they're rather different, actually.  For example, consider two lenses:  a 50 / 1.4 and a 50 / 2.8.  Both lenses peak at f/4 and have the same resolution stop-for-stop, but the 50 / 1.4 is significantly softer wide open than the 50 / 2.8.  It seems to me that your definition of of "not very good" would make the 50 / 2.8 a superior lens to the 50 / 1.4, whereas I would consider the 50 / 1.4 the superior lens, since it could do everything the 50 / 2.8 could do, and more.

I think you "derailed" a bit here Joe. What we were talking about was not my definition of "not very good" but my definition of "not very good wide open". While the 50/2.8 would be better than the 50/1.4 wide open although not necessarily a better lens for the reason you point out, that's slightly beside the point here. So let's backtrack.

Hen3ry said that you needed expensive lenses for that razor-thin DoF with FF. You objected that there were quite a few fast primes for FF that aren't particularly expensive. And I objected that many of those were'nt very good wide open whereas most of those available for MFT are. So we're talking about differences between fast primes, not fast versus slower primes.

Have a look at these

versus these

That said, as your images convincingly demonstrate, it is certainly possible to take excellent pictures with the not so expensive Canon lenses you exemplify, at least under certain conditions. One reason why I have become more picky when it comes to wide-open performance is that with MFT, the likelihood that I would want to shoot wide open is, for obvious reasons, significantly greater than it was when I shot FF (film).

Most MFT lenses are just marginally worse wide open than at peak, which they typically reach at f/4 in the center and at f/4 or f/5.6 at the edges. Since I want to use the really wide apertures far more often with MFT, due to the DoF "bonus", this is a blessing (and one of the things that convinced me to take the plunge).

I think in terms of the resolution of the final photo for a given DOF.  That is, if f/4 on mFT outperforms f/8 on FF, or f/2 on mFT outperforms f/4 on FF, then I would consider the mFT combo to be superior.

Outperforms and outperforms. How about roughly equivalent.

I wouldn't even say "roughly equivalent" -- it would depend on the particular lenses we are comparing.

Of course it would. What I said was tounge-in-cheek (as indicated by the smiley). I don't think that MFT at f/4, as a rule, would outperform FF at f/8, though I don't think there would be much of an FF advantage either, especially if sensor resolution were kept constant. At f/2 versus f/4, FF would probably win most of the time, but again, the difference wouldn't be all that pronounced thanks, primarily, to the pretty convincing f/2-performance of many of the fast MFT primes.

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