There are many small improvements in the Sony alpha 7II over the alpha 7 which it replaces. There is one big one: the in-body stabilization system (IBIS), which Sony calls SteadyShot. It has the potential to reduce the effects of camera motion somewhat when used with lenses that have optical stabilization, and a lot in lenses that don’t.
How well does it work?
I employed a test protocol based on one I developed some time ago for measuring the effect of shutter vibration on handheld image sharpness.
- The camera: the Sony a7II.
- The lens: the Sony/Zeiss (aka Zony) 55mm f/1.8 Sonnar FE.
- The filter: Heliopan 77mm variable neutral density.
- The lighting: a single Fotodiox LED-200WA-56 daylight balanced flood.
- ISO set to 800, f-stop set to 8,
- Focusing in single shot AF mode with the medium focus area setting,
- Drive set to single
- EFCS on
- Manual exposure mode.
- Hold the camera in the “Pete Souza” grip: left palm under base, left fingers bracing the underside of the front part of the lens, elbows against chest.
- Exposure protocol: ND filter to minimum attenuation,, shutter to 1/250 second, make 16 exposures with new focusing for each, ND filter down a stop, make 16 exposures… until you get to 1/15 of a second or so.
- Inhale, exhale, brace, think calm thoughts, squeeze the shutter release, remembering to “pull through”.
- Develop in Lightroom 5.7.1 with standard settings.
- Crop, export as TIFFs, analyze for horizontal edge and vertical edge MTF50 in Imatest.
- Export the results to Excel, crunch the stats, and graph.
The envelope, please:
The vertical axis is the MTF50 for the image: the point where, as the spatial frequency of the subject matter increases, the response on the sensor is reduced to half its very-low-frequency value. The units of spatial frequency are cycles per picture height. Since the a7II has a picture height of 4000 pixels, the highest that the MTF50 should ever get is under 2000 cycles per picture height. 1500 is exemplary performance. Lr does do some deconvolution filtering, which increases MTF50.
The horizontal axis is the shutter duration. 0.004 seconds, the number at the left edge, is 1/250 second. 0.064 is 1/15 second.
The heavy lines are the average for all 16 exposures. The red is with IBIS on, and the blue is with it off. The light lines are the average plus one standard deviation and the average minus one standard deviation. If the statistics for handheld MTF50 turn out to be Gaussian, about two thirds of the images will fall between the two narrow lines.
The top curve is horizontal resolution (vertical edges), and the bottom for the vertical resolution (horizontal edges) I held the camera in landscape orientation. The reason the vertical numbers are larger than the horizontal ones is that the Sony a7II, like the a7, has an anti-aliasing filter that is stronger horizontally than vertically. In fact, in both cameras, it doesn’t seem like the AA filter does much of anything vertically.
What are we to conclude from these curves? Here’s what I think
1/15 second is marginal with SteadyShot on, and just plain soft with it off.
1/30 second is OK with SteadyShot on, and just plain soft with it off.
1/60 second is good with SteadyShot on, and just marginal with it off
When we get to 1/125 and 1/250 second, SteadyShot makes a small improvement in the average image sharpness. But look at the difference in the spread between the mean-plus-standard-deviation and mean-minus-standard-deviation lines! Steady shot provides a lot more confidence that any given expose will be tack sharp. That’s worth a lot
Two thumbs up.