# Macro Extension Tubes: A way to calculate increased magnification with length of extension?

#### cayenne

##### EOS 5D Mark IV
Hi all,

Is there a formula to figure out how much an certain sized macro extension tube will increase the magnification of a macro lens given it's tube length?

Let's say I have 2 macro tube extensions:
1. A 36mm tube (empty tube no optics on any of these)
2. A 20mm tube

Let's say I'm gong to use this with my Canon 100L macro which is 1:1 magnification.

So, if I add the the 36mm, to it...will that increase the magnification of the 100L? If so, is there a way to figure how much increase from 1:! when adding x millimeters of tube?

What would 20 be? What would stacking 36 and 20 give to the 100L's normal 1:1?

Cayenne

#### Mt Spokane Photography

##### I post too Much on Here!!
Try Here:

The information for many lenses is in the lens information charts at TDP.

for example:

100-400mm II

cayenne

#### stevelee

##### FT-QL
A search for "extension tube calculator" will give you many online options.

You can consult Canon's manuals for each lens. For example the 100mm non-L macro lens will give you up to 1.19x magnification with a 12mm tube, and 1.39x with a 25mm tube.

cayenne

#### cayenne

##### EOS 5D Mark IV
GREAT INFO!!

Thank you, I"ll research on this!!

C

#### stevelee

##### FT-QL
Also, I've run my own tests on several lenses, including zooms at different focal lengths. I used two tubes totaling 32mm and photographed a ruler as close as the lens would focus. In Photoshop, I went to Image Size, turned off resampling, and set the picture width to 36mm, as an approximation of the sensor size. That way the ruler tool would give me a readout of the actual size on the sensor (more or less). So if I measured an inch on the ruler and the info panel told me the image was 1.47 inches, I figured that the magnification must be around 1.47x. That is the result I got with the 16-35mm lens at 35mm with 32mm in tubes. With the non-L 24-105mm lens and 32mm tube length, I got 1:1 for 32mm focal length, and 0.53x for 105mm.

I think some of my results with the 24mm TS-E and my 100mm macro lens are posted in a couple other threads. The extension tubes were delivered the day before I had to send the 24mm back, so I wanted to try some things with it, mainly to use the tilt for depth of field. I recall getting 2x with the macro lens and some tubes, but I don't recall the tube length I used. My notes are somewhere around here.

cayenne

#### stevelee

##### FT-QL
I see that the 100mm macro got 2.07x magnification with 68mm of tubes.

cayenne

#### stevelee

##### FT-QL
Using rule-of-thumb calculations, you would expect that to get 1.68x.

cayenne

#### koenkooi

##### EOS R
Using rule-of-thumb calculations, you would expect that to get 1.68x.
The 100mm is 70mm at close focus due to focus breathing.