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09-28-2013, 12:54 PM   #1
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Lens adapters can be useful things sometimes, letting you mount one brand of lens on another brand of camera.

One thing that has always bothered me, though, is the idea of doubling the number of lens-mount interfaces. When you look at the thick metal pieces on the front of the camera and the back of the lens, and then consider that they have to be lined up exactly parallel to the image sensor, it’s kind of amazing it works.

Although it doesn’t always work. Lloyd Chambers first reported years ago that with high-quality, wide-angle lenses you could detect very small misalignments in the camera-lens mount. Misalignment of 10 microns from side-to-side was enough to cause blur on the sides of the image. Since then a lot of other people have confirmed the same thing.

So when I hear people cavalierly talking about putting an adapter on their camera I tend to cringe. When a single camera-lens interface has enough variability to sometimes be visible, adding another large piece of metal with another mount interface seems a recipe for problems.

Don’t get me wrong. Generally, they’re acceptable or people wouldn’t use them. But I always am curious about what acceptable looks like in the lab.

09-28-2013, 01:07 PM   #2
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Wonder how many reports of soft on the edge or other issues are caused by the camera mount being off a smidge one way and the lens mount being off a smidge someplace else. One of those things I just took for granted but the tolerances should be very tight on this. I've noticed that Limited lenses seem to be harder to turn in the mount, possibly the mount is built to tighter spec? I've also noted that Sigma lenses seem to be fairly 'loose' in the mount compared to Pentax.
09-28-2013, 01:16 PM   #3
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True. I notice this with my m42 adapter and lenses with narrow base, like Helios 44. the genuine Pentax adapter has a little wobble, which can make one part of the photo less sharp, because it is wobbled differently as you are focusing and composing, than it is when you press the shutter. And the focus plane being off is almost like a tilt lens lol
Similarly, I think my Samyang 14mm is a little off, the left side is not perfectly sharp when I take photos of stars (stars look like lines, but only on the left half of the photo) - I assume its because either one of the elements or the mount is just a little misaligned. Not 100% parallel, and with 14mm, that becomes noticeable

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