So far I've been very pleased with my new Kenko extension tubes. I'm glad that I bought this cheaper set rather than spending a similar amount on a single Canon tube. I've got far more flexibilty and as I've read elsewhere, Kenko air is just the same quality as Canon air.

Anyway this experiment was designed to help me understand more about the tubes and what selections I should make for any given shot. If anyone else finds it useful, that's a bonus.

The table below gives my approximate figures for how far away the lens needs to be from the subject and how much larger I can expect the image to look. These aren't what are claimed by the manufacturers. For example on the 50mm lens it cites a minimum of 45cm to focus. Perhaps I am rather less fussy than Canon enginineers about what is focused but I made this figure 35.5cm. Then again it might be (can anyone help?) something to do with my camera having a cropped sensor.

a b c d
a 50, b 0mm, c 35.5cm to ∞, d 1.0
a 50+12, b 12mm, c 14.5 to 22.5cm, d 2.6
a 50+20, b 20mm, c 13 to 15cm, d 2.9
a 50+12+20, b 32mm, c 9cm, d 4.5
a 50+36, b 36mm, c 7cm, d 5.1
a 50+12+36, b 48mm, c 5cm, d 6.5
a 50+20+36, b 56mm, c 5cm, d 6.6
a 50+12+20+36, b 68mm, c 4cm, d 8.0

a) Lens/Tube Combination
b) Total Tube Length
c) Approximate Focusing Distance
d) Approximate (Linear) Enlargement Ratio

Very interesting post :-) jet28 · 2008-12-06: 02:49

good test! I do not know what affect Lengthening rings on the scale, but wanted to buy the ring, your post helped me. Thank you! BVM33 · 2008-12-06: 08:16

interesing post nikito · 2008-12-06: 08:31

Interesting sequence peregol · 2008-12-06: 12:23

Good study! You've also introduced me to Kenko extension tubes. Am keeping them in mind for a future purchase. Nubster · 2008-12-06: 16:03

Tagged: macro stamps extension tubes 12mm 20mm 36mm 50mm