RogerBW's Blog

Extension tubes 13 September 2017

Thanks to a blog reader, I borrowed some more macro equipment.

This time I used an actual scale; here's a wooden ruler, numbered in cm, mm graduations. This uses the 14-45 kit lens, zoomed in to 45mm, as do most of the following. 41 pixels/mm.

With the 16mm extension tube (from a Kenko DG extension tube set). I had to lift the ruler off the table. 95 pixels/mm.

With the +10 macro lens, lifted again. I think the lens photo looks sharper than the tube one, though there's no particular reason why that should happen. 78 pixels/mm.

The full 26mm of tube. 150 pixels/mm.

+17 dioptres of macro lens plus 26mm of tube on the 45mm. This actually works surprisingly well. 195 pixels/mm.

Everything! +17 dioptres of macro lens, 26mm of tube, and 200mm main lens. (I was moving the subject to try to get it in something like focus. With a more flexible tripod system so that both camera and subject could be braced at the right distance from each other, this would probably work better.) 857 pixels/mm. Which is scarily close to optical limits: visible light wavelengths are conventionally 400-700nm, so there are only about 1½ to 3 wavelengths per pixel here.

Compared with the lenses, the tubes are about as bulky to store, quicker to get on and off (I'm very impressed with the manufacturing quality), but don't seem to be any better in terms of image quality. The lenses are more flexible, since there are four of them, and explore the lower-magnification side of things more effectively. The tubes are also about five times the price of the lenses; oh well.

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  1. Posted by Owen Smith at 02:29pm on 13 September 2017

    They're my extension tubes, and I didn't pay Amazon's £100 price. I'm sure they were more like £60, I bought them from an online photographic specialist retailer though I can't remember which one.

    There is a reason the extra lenses might be sharper than the extension tube for the same magnification (you actually used a bit less magnification with the lenses). As I commented on your last blog post on this, Micro Four Thirds lenses are not geometrically correct and the camera corrects for that plus chromatic aberrations in software. The camera still thinks you are at 45mm focal length, but it's all thrown off by the extension tube so the edges of the sensor are seeing light from nearer the middle of the lens than they would normally and the camera is still applying the corrections for the edge of the lens. How much that matters I don't know.

    The add on macro lenses by contrast still have the light from the main lens striking the parts of the sensor that they are supposed to so the right corrections are applied, just nothing extra is being applied for the macro lens.

    I note neither Panasonic nor Olympus sell extension tubes for Micro Four Thirds. This potential problem with the software corrections may be why. Either that or they'd rather sell you a macro lens at more cost and profit than a set of extension tubes.

    I agree the mechanics of these extension tubes feels exceptionally good. I found no looseness of the entire combo, even with both tubes mounted and a big lens.

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