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

[cayenne]

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?

Thank you in advance!!!

Cayenne

 

[Mt Spokane Photography]

Try Here:

The Ultimate Guide to Extension Tubes

Extension tubes are a cost effective way to get macro-like shots using your existing lenses. In this guide we'll examine exactly how and when to use them.

shuttermuse.com

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

for example:

100-400mm II

Canon EF 100-400mm f/4.5-5.6L IS II USM Lens Specifications and Measurements

Review manufacturer specifications and detailed lab measurements for the Canon EF 100-400mm f/4.5-5.6L IS II USM Lens. Compare the specs and measurements of this lens with other lenses.

www.the-digital-picture.com

 

[stevelee]

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]

GREAT INFO!!

Thank you, I"ll research on this!!

C

 

[stevelee]

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.

 

[stevelee]

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

 

[stevelee]

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

 

[koenkooi]

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

The 100mm is 70mm at close focus due to focus breathing.