A week or so ago, a reader asked if I could try to find out if there’s any vibration difference between a heavy carbon fiber tripod with the skinny legs extended first, or the fat legs extended first. I was doubtful that there would be any difference, and first tried to find out if there was measurable vibration with the skinny-leg-first regime.
I mounted the Zeiss 135mm f/2 Apo-Sonnar to a Nikon D810. I mounted a RRS L-plate, clipped it in landscape orientation into an Arca Swiss C1 head which was attached to a set of RRS TVC-44 legs. There are four leg sections in this tripod; three nested in the one that’s attached to the top plate. I extended the two skinniest legs.
I lit an Imatest SFRPlus target with a Paul Buff Einstein strobe set to 2.5 watt-seconds, which gives a 1/13000 second strobe duration. I set the ISO to 100, the shutter speed to 1/250 second, the shutter mode to 3-second delay and electronic first curtain shutter (EFCS), set the mode to mirror up, focused wide open, and set the aperture to f/5.6. I double tapped the shutter release 16 times. That gave me a set of baseline images with no — or at least minimal — vibration-induced blur.
Then I lit the target with a Fotodiox variable-output 5500K LED light. I set the power to max, and made 16 exposures at 1/125 second. I dialed the light down a stop, and made 16 exposures at 1/69 second. I kept doung that until I got through the 1/15 second sequence. I developed the images in Lightroom 5.7.1 with sharpening and noise reduction turned off, exported them as TIFFs, and measured on-axis MTF50 in both the vertical and horizontal direction.
The top graph is for horizontal lines, and the second is for vertical ones. The thick lines are the mean values, and the thin ones are three standard deviations higher and lower. You can see that the higher shutter speeds are more problematical than the lower ones, though the differences are small. That’s because the time the second curtain is moving is a larger portion of the time the shutter is open when the shutter speeds are shorter.
You can also see that, since the shutter moves up and down, it affects the horizontal lines a bit more than the vertical ones.
You can also see that the effects are very small. One day, we’ll have global shutters, and the curves will be virtually flat.
But back to the issue at hand. It looks like there’s maybe a statistically significant worsening in the spread in the horizontal sharpness of the 1/125 second exposure over the strobe-lit one, even if the mean is about the same. The mean values for the two slower shutter speeds, both vertically and horizontally, are actually fractionally better than the strobe-lit case.
I dunno. I’m thinking that there will be too much variation introduced by taking the camera off the tripod, adjusting the legs, putting it back on the tripod in as close to the same place as the first time, refocusing, and making a new sequence to answer the original question. And anyway, from the tiny differences between the strobe-lit and continuously lit cases, if there is any difference, it’s unimportant in this case.
By the way, 1700 cycles/picture height is 0.344 cycles per pixel. That’s a very sharp lens!
Note the over and undershoot from the Lr default sharpening, which makes the MTF50 higher than it would be if there were no sharpening.