There was a recent post on DPR that showed dramatic effects on bokeh of EFCS. It was a apples/oranges comparison, with the mechanical and EFCS shutter speed different from each other, and the EFCS set to 1/8000, which is clearly out of the range where EFCS usually works well.
Still, it got me thinking, and I ran a quick test with a Sony a7RII and the Sony 90mm f/2.8 macro lens. I set the lens wide open, and the ISO to 640. I lit the subject with a Westcott LED panel, with color temperature set to 5000K and output on full. That gave me 1/1000 second shutter speed. I made exposures with EFCS on and off. Then I turned the light down a stop, and did the same at 1/500 second. I continued along those lines until I got to 1/60 second.
I developed the images in the current version of Lr CC, with default settings except the WB was set to 5000K/0, and a slight exposure boost.
Here are the images:
There are some exposure variations at higher speeds. We expect this. The bokeh differences appear to be minimal to me. However, in theory, there should be bokeh effects of EFCS at high speeds, since the electronic first curtain is in a different plane than the mechanical first and second curtains. Thus, depending on the characteristics of the lens the subject distance, the f-stop, and the place where you look in the image, we should see some differences. They don’t appear to be important here — the exposure variation is more noticeable — but they probably would be at higher shutter speeds.
That’s moot, because we probably wouldn’t use those speeds due to exposure variation. I’ll make some more tests with other lenses.
Lynn Allan says
I don’t see any difference either.
Was the expectation that the light waves “flowing past the diaphragm blades” would be different with the shutter itself in a slightly different plane?
Isn’t the diaphragm in the same place, regardless of EFCS or not?
Some of the article was “over my head” … less so than many articles, but I especially don’t understand the concluding statement:
> That’s moot, because we probably wouldn’t use those speeds due to exposure variation. I’ll make some more tests with other lenses.
And again: the blog shows “One Thought”, but I don’t see any comments. Your’s missing? I tend to be especially interested in blog articles with one or several comments. I really doubt you are trying to “click bait” me 🙂
The difference is that the two shutter curtains are in different planes when EFCS is selected, and the symmetry of the shadows of the two curtains in fully mechanical shutter is lost. Horshack did a good post on this on dpr. Maybe I can find it.
Lynn Allan says
My bad? in previous comment. I don’t really understand bokeh, and may have confused it with diffraction at closed apertures like f11 and more closed.
Maybe put me on the blog’s “ignore filter”? 🙁
You’ll be pleased to know that I don’t have an ignore filter, except Akismet.
Lynn Allan says
Just curious … right now my browser shows 4 comments instead of 3, before I submit this one. Will your browser show an accurate number of 4 once this comment is accepted?
This glitch also happens with Chrome, IE-11, and Edge on Win-10. Am I the only experiencing this?
Another OT question: Have you submitted this series to any of the DPR forums? It doesn’t “fit” for the Sony e-mount forum that I am most active on. I do occasionally check “Science and Tech”, Printing, Retouching, Canon full-frame, and Nikon One.
It does seem your blog articles get a lot more participation on the HUGE DPR forum, which makes sense, but has mixed benefits.
After approving your comment, and before posting this reply, I see five comments, one of which is a pingback. Maybe you’re not counting the pingbacks?