Extension tubes

[glitch]

Is there some way of working out what the effective focal ranges would be on a certain type of lens with various tubes attached? Is it relatively simple maths or is there some sort of conversion chart you can use? I recall someone mentioning that the Kerso tubes came with some sort of Image Magnification table on the instruction leaflet, but I don't own a set and therefore don't have access to that information.

I'm looking to hopefully pair a set with a Canon TS-E 90mm f/2.8 lens but I'm not sure what the overall effect(s) would be.

 

[jgs001]

Have a look here:

http://www.macrobellows.com/using_tubes.php
and
http://www.macrobellows.com/technique.php
The tables are all for using a 50mm lens.

Based on the tables and things I've read, it's the length of the extension tubes divided by the fl of the lens to get the magnification (I think that's for normal lenses though.

 

[Canon Bob]

On the TS-E90, you'll get the following;

12mm tube will give you a magnification range of 0.43-0.14x at a working distance of 264-691mm
25mm tube will give you a magnification range of 0.60-0.31x at a working distance of 207-345mm

Going much beyond this gives such a narrow range of working distance that framing becomes difficult and it isn't really practical.

HTH

Bob

 

[glitch]

Have a look here:

Thanks for those; they'll make for interesting reading.

On the TS-E90, you'll get the following;

HTH

Bob

Nail. On head. Hit.

Bob; I thank you once again.