April 25 2011 - Photo Jottings

April 25 2011


Will cheap APS-C only lenses handle 24mp resolution?

Some people are asking if the fictitious A700 replacement camera, (announced well over a year ago, and now known as the A77) which uses a new 24mp APS-C sensor, will be too much for the older APS-C only lenses, which were designed for 6mp, 10mp, and 12mp sensors, depending on how far back you want to go.

The answer, based on some simple tests with the 24mp Sony A900 is yes, most lenses should be able to show more resolution. Obviously, all the lens’ optical faults will be more noticeable, but that’s just the way it is.  I find the newer APS-C lenses seem better than the rebadged Sony full frame lenses, and much cheaper.  Look at the newest Sony “DT” lenses, like the excellent 35/1.8; its performance in some ways is superior to the (equivalent FF coverage) 50/1.4, which is better built, but a little outdated and more expensive.  So what I’m trying to say here is; just because a lens was designed for a smaller sensor, doesn’t mean it’s inferior to a full frame compatible lens.

Below are two crops from full size images, the top crop is from the Sony 16.2mp A580 and the bottom crop from the Sony 24mp A900. The lens used is the Tamron 60mm F/2 macro, which is for APS-C cameras only.  Note; I also tested the Sigma 10-20mm F/4-5.6, which responded about the same way as the Tamron.  I matched both APS-C and full frame capture areas by moving the camera and tripod, that’s why the perspective is different, and done this way replicates a 24mp APS-C sensor.  Bracket focusing (focus point is the “Grand Canyon” dream catcher on the cap) was used until the sharpest image was produced for each camera.  The A900 APS-C size capture feature is turned off of course.  Both images are from RAW.  The A580 crop has been upsized to match the A900 size, which makes it easy to see the differences.  The A900 has a slight disadvantage here, as the final capture area was a little smaller than the A580, but not really enough to be noticeable. It may look like there is a depth of field issue at the top of the cap, but that’s not the case, it’s the smaller detail in that areas that’s more apparent with the 24mp sensor, that’s why I used the cap with a fine weave.  I used F/5.6, 1/4 sec, WB 3100k trimmed to M3, ISO 200.

A580 with Tamron 60mm F/2 macro.
A900 with Tamron 60mm F/2 macro
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