Jeepers Creepers, Where'd Ya Get Those Peepers? Part 2.

The saga continues...

Previously on Jeeper Creepers: A young lad in North Dakota discovers the allure of photography when he finds his father's Kodak "Pocket" camera and learns about aperture and shutter speeds by opening the back of the camera and watching what happens when the shutter release is pressed (more here). Later he graduates to a Brownie Hawkeye, then a 35mm rangefinder, and then a SLR with interchangeable lenses. He is hooked...

In my last post, I described some unexpected results when comparing a micro four thirds camera (Olympus OM-D E-M10) and an APS-C camera (Sony A77II). It might be fairer to say I am comparing lenses, namely, the Olympus M.Zuiko 75-300mm f/4.8-6.7 II MSC ED zoom and the Sigma 120-400mm f/4.5-5.6 APO DG HSM. All I wanted to know was, how much difference is there between MFT and APS-C. I got more than I bargained for...

In my earlier comparisons I was surprised that the smaller sensor E-M10 images appeared to be sharper than the larger APS-C sensor images (for more on sensors, click here). But, I was trying to recreate a realistic shooting environment by handholding and using a fairly fast shutter speed. I decided that I needed to be a little more disciplined if just good image quality was my sole objective.

I tried a number of things, with use of a tripod probably being the most important. Although, quite frankly, with the image stabilization built in to both the E-M10 body and the A77II body, I'm not sure it really made that much difference, particularly when using shutter speeds of 1/500 sec and faster. Still, using a tripod took the camera shake variable out of the picture (pardon the pun). Even with a tripod, however, there are a couple of other considerations, which we will explore as we go along.

First let's agree on some fixed constant. Most photographers would agree that the best image quality should be at some aperture other than wide open (subject to spherical aberration, coma and astigmatism) or closed down to the minimum (diffraction reduces sharpness). It's simple physics. A lens can not be optimized across its entire surface, so in almost all cases the optimum image quality is somewhere in the middle aperture range, in fact usually one or two stops smaller than the maximum in order to allow the most light possible while providing the optimum lens corrections. For example, here is the difference between f/6.7 and f/11 on the E-M10:

Olympus 75-300mm f6.7 vs f/11 @300mm (100% crop)

F/16 looks marginally better, but interestingly f/22 is less sharp. As the lens approaches its smallest opening diffraction rears its ugly head and IQ suffers. For our purposes let's stay at f/11.

So, how much difference does a tripod make? When I compare the Olympus handheld shot at 1/2000 sec against a tripod shot at the same f stop but a shutter speed of 1/500 sec, I see virtually no difference at max zoom (300mm). I would hope I never shoot at any less than 1/500 sec except for extreme cases. However, for the sake of argument, let's compare the shots on a tripod. Oops. We already did. The comparison shots above were taken on a tripod.

Next comes the argument that shooting on a tripod can be worse UNLESS you disable the IS (image stabilization) feature. I have seen some pretty extreme examples - supposedly any movement is picked up by the IS and an anti-movement adjustment mechanism goes into a loop, picking up the movement caused by the mechanism. I don't see this with these two cameras.

So, we are down to lenses, or more properly, the Sigma lens. Here is just the Sigma compared at max aperture (f/5.6) and close to optimum (f/11):

Sigma 120-400mm f/5.6 vs f/11 @400mm (100% crop)

There is some kind of strange aliasing going on in the f/11 shot. Like a double exposure or something. And, it gets worse at f/16! The mystery only deepens...

Any suggestions? The only thing I can think to do is get my hands on another 400mm and see what kind of results I get.