Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

Started Jun 16, 2014 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

Just another Canon shooter wrote:

Anders W wrote:

As to diffraction, the larger format has an advantage when comparing at the same (rather than equivalent) f-stops. At equivalent f-stops, there is no difference at all, and the impact of diffraction is generally trifling at wide apertures.

At equivalent stops, the smaller format lens can NOT be a scaled down version version of the larger one.

Of course it can. For example, the MFT 25/1.8 at f/1.8 would be equivalent to the FF 50/1.8 from which it was scaled down at f/3.6.

But 25/1.8 is NOT a down scaled version of the 50/3.6! Your scaling argument falls apart at equivalent settings. You need to scale the whole world, wavelength and light density included for that.

I am not arguing that the smaller format can keep up with the larger at equivalent apertures no matter where across the aperture range we compare. It can keep up well enough for my standards in the range I am interested in using, i.e., primes with a max speed somewhere between f/1.7 and f/2 (if it is FLs within the standard range we are talking about) and that's all I care about.

My point is that the "enlargement theory" proposed in the OP of this thread is wrong. Whatever advantages the larger format has, that's not the way it gains them. Rather, the simple truth is that it is easier, regardless of sensor size, to make an f/2.8 normal lens that performs well wide open than to make an f/1.4 normal lens that performs similarly well wide open. The aberrations you have to correct for decent performance are simply smaller at f/2.8 than at f/1.4 and that's it.

The lowly Canon 50/1.4 at f/4 beats the Panasonic 25/1.4 at f/2 by a comfortable margin (PZ) both in the center and at the borders,

Did you see the big sign on PZ's home page saying that their results are not comparable across sensors/platforms? Here is my previous example augmented with the PL 25/1.4 and the Canon 50/1.4 based on reasonably comparable data. Personally, I prefer the 20/1.7 to the 25/1.4. Note that the 20/1.7 at f/1.7 is roughly on a par with the Canon 50/1.4 at f/2.8, and significantly sharper at f/2.8 than the Canon at f/4, in spite of the lower pixel count of the sensor.

The figures are line pairs per image height at MTF-50, center/average, based on unsharpened output from RAW files.

Panasonic 20/1.7 on E-M5 (16 MP)

1.7 870/735

2.8 1050/875

4.0 1075/880

Panasonic 25/1.4 on E-M5 (16 MP)

1.4 690/590

2.8 960/820

4.0 980/850

Leica Summilux 50/1.4 on M9 (18 MP, no AA filter)

1.4 600/530

2.0 950/740

2.8 1025/860

4.0 1110/980

Canon 50/1.4 on 5D2 (21 MP)

1.4 650/530

2.0 790/660

2.8 920/690

4.0 960/890

and I am not even mentioning the new Sigma 50 here which might very well be sharper wide open than anything you own at any aperture.

While the Sigma is a nice lens, I don't think it would be sharper wide open than anything I own at any aperture. I wouldn't be interested in it anyway. As I said, I don't find much need for the shallow DoF that comes with a 50/1.4 wide open on FF and the lens is big and heavy. I'd much rather have the FL control (more lenses in my bag rather than in a drawer back home) that I get with MFT.

 Anders W's gear list:Anders W's gear list
Panasonic Lumix DMC-G1 Olympus OM-D E-M5 Olympus E-M1 Panasonic Lumix G Vario 14-45mm F3.5-5.6 ASPH OIS Panasonic Lumix G Vario 7-14mm F4 ASPH +28 more
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