This is the third of three instalments on the comparison of three sets of macro extension tubes for MFT cameras: Macro extension tubes (description), Macro extension tubes (glare), and Macro extension tubes (lens mount).
Disclaimer: I have no connection to any of the suppliers of the items compared in this test. I bought them from different on-line sellers. Although some of the products I bought have serious design flaws I have tested only one copy of each, bought in July 2017 (Kenko), June 2017 (COMIX), October 2015 (PIXCO). The items in production at the time you read this post may be of an updated design or quality. It is also necessary to be aware that in the case of some Chinese brands, cheap and expensive versions of an item may exist.
As yesterday’s tests showed that the 45 mm f/1.8 general-purpose prime lens had, when used at high magnification, rather bad performance in the corners and edges of the image, I used the M.Zuiko 60 mm f/2.8 macro for the two tests described here.
In the second and third tests, described in this post, my aim was to test the lens mounts, first for light leaks, and second for mechanical fit.
For the second test the two LEDs were positioned one on each side of the tubes at the position of the mount between the two tubes in each pair. The lens cap on the lens, and room in almost darkness except for the two LEDs. Camera set to ISO 25600 and exposure time 10 s (f/11, but this is irrelevant as the lens cap was on and no light passing through the lens). The results of this test were good. The mounts in all three sets did not allow light through.
For the third and fourth tests both LEDs were positioned pointing downwards towards the target. The camera was as before carefully levelled and I assessed whether any gross focus problems were visible in the images. To my eyes, there were none. It should be remembered, though, that with the lens pointing downwards, the possible effect of the weight of the lens on axial misalignment was minimised. I do see slight overall softness with the COMIX tubes, but it is likely to be caused by internal reflections, still degrading image quality in a situation where glare was not expected, as no strong off-axis light source was included in the setup.
Differences in sharpness anyway are very small and not detectable reliably with this simple test. The slight softness due to glare, seems to be a small but consistent effect under this test.
In the last test I looked at the play in the mounts. Inserting two tubes between camera and lens, add three new possible sources for play and misalignment. Tubes are used to increase image magnification, and consequently also decrease depth of field. For this test I simply very gently push the lens while keeping the tripod as steady as possible.
I was not sure on how to show how play in the mounts affects the image when working at rather high magnification, so I recorded a short video (hosted at YouTube because of wordpress.com free account restrictions), while moving the objective by softly pushing it and moving in the mount while keeping the camera and the photographed SD card adapter still (there was slight vibration due to camera shake, but it was very little compared to how much the play in the mount displaced the image projected on the camera sensor). To give an idea of how much play there was, by lightly pushing the lens “nose” it was possible to move it by a few millimetres while keeping the camera steady.
While the Kenko and PIXCO tubes have little play in the mounts, not causing trouble, the COMIX set has an awful lot of play, so much as to make this set of tubes completely useless. The surface of the mounts in the PIXCO is rough, while in the Kenko ones smoth, and in the COMIX shinny and smooth. When a lens is mounted on the PIXCO adapter a gentle grinding vibration and noise are felt. The surface of the tube has developed some use marks, so it could potentially be a source of dust particles.
CONCLUSION: Extension tubes are hollow tubes, but they still differ dramatically in how usable they are! The amount of play in the mounts of the COMIX tubes is so extreme and the springs so weak as to make them unable to keep any objective at a repeatable position, which is a requirement for successful macro photography. Do take this into account when buying cheap pieces of optical equipment.
All illustrations, text and measurements are of my own authorship, and copyrighted.
(c) 2017 Pedro J. Aphalo