20. Posting Stamps

by Jarvo J December. 06, 2008 11213 views

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

50mm lens, no extension tubes.
Approximate Focusing Distance 35.5cm to ∞
Approximate (Linear) Enlargement Ratio 1.0

50mm lens, 12mm tube.
Approximate Focusing Distance 14.5 to 22.5cm
Approximate (Linear) Enlargement Ratio 2.6

50mm lens , 20mm tube.
Approximate Focusing Distance 13 to 15cm
Approximate (Linear) Enlargement Ratio 2.9

50mm lens, 12mm and 20mm tubes.
Approximate Focusing Distance 9cm
Approximate (Linear) Enlargement Ratio 4.5

50mm lens, 36mm tube.
7cm Approximate Focusing Distance
Approximate (Linear) Enlargement Ratio 5.1

50mm lens, 12mm and 36mm tubes.
Approximate Focusing Distance 5cm
Approximate (Linear) Enlargement Ratio 6.5

50mm lens, 20mm and 36mm tubes.
Approximate Focusing Distance 5cm
Approximate (Linear) Enlargement Ratio 6.6

50mm lens, 12mm 20mm and 36mm tubes.
Approximate Focusing Distance 4cm
Approximate (Linear) Enlargement Ratio 8.0

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There are 5 comments , add yours!
Susan 12 years, 2 months ago

Good study! You've also introduced me to Kenko extension tubes. Am keeping them in mind for a future purchase.

12 years, 2 months ago Edited
Peregol 12 years, 2 months ago

Interesting sequence

12 years, 2 months ago Edited
Nikoleta Mladenova 12 years, 2 months ago

interesing post

12 years, 2 months ago Edited
Vadim 12 years, 2 months ago

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!

12 years, 2 months ago Edited
Jet28 12 years, 2 months ago

Very interesting post :-)

12 years, 2 months ago Edited
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