This massive 300mm extension tube for Canon cameras is a little bit over the top, but allows you to achieve ultra-macro magnifications beyond 1x using long lenses! (100mm+)

It reuses the metal mount pieces from Kenko extension tubes to make mating it with your lens and camera smooth, but replaces the original lens contact system with its own. This preserves the electronic aperture and autofocus control of your lens.

The advantage of using a long extension tube with a long lens (rather than adding a close-up lens) is the exceptionally high working distance it allows, see the performance notes below.

The assembled weight is 340 grams.

If you're interested in something a little less ridiculous, a 150mm version of the tube is also provided.

300mm tube performance with the Sigma 180mm f/3.5 APO Macro DG HSM

Minimum magnification 1.7x at 240mm working distance
Maximum magnification 5x at 170mm working distance (That means that a subject 7.2mm x 4.8mm completely fills the frame!)

Compare these numbers to the bare Canon MP-E 65mm, which offers a similar magnification range:

Minimum magnification 1x at 100mm working distance
Maximum magnification 5x at 41mm working distance

Lens notes:

• Huge focus dial throw gives a large, practical range of magnifications
• Lens collar is very helpful for mounting light accessories and to use as a handle

Performance with the Canon EF-S 55-250mm IS

Focal length 70mm: Dust on the front element is in sharp focus!
Focal length 100mm: 5.6x -> 6.3x magnification at 16mm -> 27mm working distance
Focal length 120mm: 2.5x -> 2.6x magnification at 46mm -> 51mm working distance
Focal length 135mm: 2.2x -> 2.3x magnification at 88mm -> 92mm working distance
Focal length 200mm: 1.5x -> 1.9x magnification at 267mm -> 315mm working distance
Focal length 250mm: 1.1x -> 1.2x magnification at 370mm -> 415mm working distance

Lens notes:

• Image stabilisation is surprisingly helpful for steadying the shot for framing.
• Setting the focus ring at infinity actually increases both the working distance and the magnification (because the end of the lens collapses towards the body).
• Focal lengths in the 100-150mm range are the most useful.
• At 250mm the subject is so far away that framing and lighting the subject is difficult. Maybe good for natural light photos in bright conditions?
• End of the lens rotates during focusing, but not during zooming
• Zoom position is not held very strongly - so bumping the end of the lens is really annoying
• This is definitely not an Apochromatic lens - strong longitudinal chromatic aberration present, with magenta fringes on out-of-focus areas in front of the focal plane, and cyan fringes beyond.

If you liked this tube, please also check out my twin-flash arm system for the MT-24EX that's shown in the second photo, and my diffusers for the MT-24EX.

Printing/assembly instructions

Thingiverse's new Thing display completely mangles all of my printing/assembly instructions, and it looks like there's no chance of them fixing it any time soon, so I've posted them here instead:

https://sherlock-photography.github.io/canon-extension-tube/