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As someone who uses an NEX, I'd like to understand the background of the E- and A- mounts, where Sony is coming from, and to what ends each of these mounts was designed for, and what they do or not do well.

Do the mounts have anything to do with the camera technology? Can one have an E-mount SLT / SLR? An A-mount mirrorless camera (that's roughly as small as the E-mount mirrorless cameras)?

I'm aware that A-mount is compatible with lenses that are decades old, but what are the other pros and cons of A- mount as compared to E-mount?

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These are different designs, developed at different times. Forty years have gone between each was initially launched as the A-mount was simply acquired from Minolta which had by then fused into Konica-Minolta.

The A-mount introduces AF which worked by Phase-Detection and hence lenses for that mount are designed to focus that way. Over the years, they were optimized to provide better performance with Phase-Detection, moving the lens element a set distance faster.

The E-mount is all electronic and is built for lenses which have their own stepping motors to move the lens efficiently in tiny increments which is needed for Contrast-Detect AF. Of course, since a few NEX cameras offer Phase-Detect AF too, the new E-mount lenses are designed to work with both.

Optically the E-mount requires a much shorter flange distance which too small to accomodate the mirror needed by a DSLR and most-likely an SLT. This is why no DSLR uses the E-mount. Mirrorless cameras can use both since one can bridge the gap of flange distances by adding a simple tube with pass-through electrical contacts.

Sony has such adapters which some in two versions. One for manual focus, perhaps supporting SAM lenses (someone can correct this if this is wrong) and the other for autotocus. Those have a pelicle mirror and Phase-Detect AF built-in. Additionally, both these come in APS-C and Full-Frame variants but they respective advantages are the same.

  • Which is less likely to mis-focus under low light? I'm not talking about the time it takes to focus but the percentage of photos that end up mis-focused. I use an E-mount camera, the NEX-5R, and I occasionally get mis-focused photos, whether with the 19mm prime lens (contrast-detection only) or, less often, with the 35mm prime (hybrid AF). Is an SLT likely to perform better? – Vaddadi Kartick Jun 7 '14 at 5:21
  • Let me know if I should ask this as a separate question -- how accurate is the autofocus on E- and A-mount cameras fare under low-light? – Vaddadi Kartick Jun 7 '14 at 7:18
  • There is always some chances of missing focus and there is nothing in the mount which makes one more or less likely to do so. The brighter the lens though, the more light the AF system has to work with. – Itai Jun 7 '14 at 15:15
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    @KartickVaddadi - Contrast-Detect AF is actually more accurate and most hybrid cameras like the NEX-5R switch off Phase-Detect AF in favor of Contrast-Detect in low-light. This intentionally sacrifices speed of focus in favor of accuracy. – Itai Jun 7 '14 at 15:17

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