why not f/1.2 by Sony?

Started May 14, 2013 | Discussions thread
tomtom50 Veteran Member • Posts: 3,244
Re: why not f/1.2 by Sony?

forpetessake wrote:

ilza wrote:

The photons need to follow a path through the sensor, past wires (DSLR sensors are not BSI)  before they can be counted at the photodiode, and that path is sensitive to angle of incidence, more on some sensors that on others. Quantum efficiency is not a single number; it is dependent of the angle the light strikes the sensor/microlens system.

Shadows of the wires will be longer with oblique illumination indeed.  But since wires (as visible from the sensels) form a rectangular skyscraper landscape, would not this rectangularity be visible on the shape of bokeh?  (When everything settles down, bokeh is, AFAIU, only “the shadow of the entry pupil” on the sensor.  So everything which effectively affects the entry pupil should be visible on bokeh)

Until this relation with bokeh is clarified, I like my microlenses conjecture better.

Yep, it's been explained elsewhere that the effect on t-stop is due to heavy vignetting (compensated in software). Vignetting is both natural effect of the large aperture lens as well as microlens design. It's not pronounced in the old sensors without microlenses, nor in the new designs with shifted microlenses.

Since we are discussing Sony NEX design here, there are test pictures that show that there isn't a heavy vignetting even at f/0.85, much less at f/1.2:

Your picture does not quite answer the question. Loss of oblique rays on the way to the photodiode is not limited to the corners of the frame.

A test can be made pretty simply:

- Mount the 50mm f1.2 with a dumb adapter so lens information is not transferred to the camera (ISO spoofing defeated)

- Take 'equivalent exposures at 1/3 stop from f2.8 to full open at the same st ISO (for example f2.8@1/30, f2.5@1/40, f2.2@1/50, f2@1/60 all the way to wide open.

- The exposure in the center will drop as you get wider.

- Take a few underexposed shots at f2.8 (1/40, 1/50, 1/60). These can be used to benchmark just how ineffective the wide aperture was.

- Once determining that you f1.4 acts more like an f1.8 (or whatever), see if f1.4 actually gives much more bokeh than f1.8.

I will do this myself when I get my Nikon adapter, but i have the 16MP sensor which is less problematic than the sensor in the NEX 7

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