Interesting test! Could you post some downsized images to show how you determine this? I think others would find it interesting (as well as myself).
Have you taken into account the LED's own cycle time? As with all devices, they all suffer from a "lag" of one sort or another. You might want to research online the response time of the particular LEDs that you are using. This could help you to determine a little more accuracy by taking their "fudge factor" into account.
This is why testing for such high speeds is proving difficult. I still haven't pulled my old silly-scope out of storage (not only because it's -20 F. outside lately) because I am certain that the phosphor lag on the display would again prove useless for a test of this nature.
One more thing. Have you tried using long-zoom settings and using the aperture override too, to see if you can obtain even faster speeds at f/11 (or higher?).
Also, I'm not sure what you mean when you say, "Especially the shots taken with 100% image size suffer from significant shutter distortion." Since none of these cameras use a focal-plane shutter there are no shutter distortion effects. What are you referring to here?
(p.s. Have you thought about focusing with the room lights on first? Big Grin The more "point source" your lights the more easy it will be to have their light show up on the CCD's pixels and therefor be more accurate to tell when they are fully lit or only beginning or ending their ramping or decaying light cycle.)
e2b? I'm curious on why you would create a display of white and black lines at an angle like that? Does that make it easier to count the lines?
Howver, there is also a problem with certain ways that CCDs are read-out. Some of them are read in linear banks or bands. Which, surprisingly, can cause focal-plane shutter distortions too in an electronic shutter.
Fudgey, thanks for posting all that. MOST interesting. It's odd how at such fast speeds everyone is having a difficult time trying to pin-down exactly what is happening when. I sometimes even suspect it might have to deal with ambient camera temperatures affecting shutter speeds.
From what I understand, the shutters in these cameras are both electronic and aperture working together. There should be no lowering of light levels at the edges of the frame as the aperture opens and closes to expose the CCD (which in turn is also turned on and off rapidly in sync with the opening and closing of the leaf-shutter). This is why these types of shutters are so highly prized in the range-finder style of cameras that don't depend on the slow focal-plane shutter with all their inherent exposure problems of a narrow slit moving slow over the recording media. In a leaf-shutter system, the concentrically arranged blades of the shutter open and close concentrically, just like an iris-diaphragm (and indeed in digital cameras they are usually one in the same). This diaphragm/shutter assembly is situated in the optics so that as it opens and closes all light from the lens passes through it evenly. Meaning there should be no vignetting in any area of the exposed frame. And ... just as you can set your aperture for f/2.x or f/8.0 you will see that the full frame is evenly lit, no vignetting. So the same will hold true when it is also acting as a shutter.
Howver, there is also a problem with certain ways that CCDs are read-out. Some of them are read in linear banks or bands. Which, surprisingly, can cause focal-plane shutter distortions too in an electronic shutter. I've seen some images from digicams similar to the helicopter photo that I posted, where instead of the whole blade being distorted, an airplane's prop is cut up into small bands of curved distortion, as each band of the CCD is read out too slowly. It all depends on how the data is pushed off of the CCD as it is being read. I'll have to try to find that image online again to show others an example of this electronic shutter distotion (I may have even saved it to my hard-drive, I can repost it if I find it). I don't think this affects these cameras though. I've found no evidence of this in any high-speed images I've taken to date.
Now, onto the interpretation of the partially lit LEDs ... this is indeed a head-scratcher. The first thought that came to mind is that at such high speeds, the capacitance of the wires themselves are causing the delay in the LED response time. As voltage is applied to a wire, it slowly ramps up in voltage until the wire's own capacitance has been reached and then the LED lights proportionately as the peak voltage happens. Then the reverse takes place when it is turned off. If those LEDs do indeed have such a short response time, then it can only be a capacitance problem that is causing the slowly lighting and dimming of the lights.
I find it interesting that you aren't getting the higher shutter speeds that I suspect are happening in my S3. At such high speeds, I'm thinking that not only is it dependent on very minor differences in the camera, and what settings are used (as you have seen they are also f/stop dependent), but that each make and model of camera might be able to also affect what shutter speeds are available. I'm still convinced, by looking at histograms and other tests I've done that I can get at least 1/40,000th of a second, and perhaps even 1/64,000th of a second on the S3.
Looking forward to seeing any other tests you might find (if you tackle it more). And thanks for posting what you have so far. It's nice to know that I'm not alone in trying to find an easy and definitive way to test exactly what is going on. If nothing else, I'm so glad to now have shutter speeds that will stop a hummingbird's wings without using flash. I'm an available light addict. Nothing I hate more than ruining an image by having to result to using flash. These new shutter speeds will open up nature-photography doors that I didn't even get to peek through in the past.
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