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The Canon MP-E 65mm works differently than my other macro lenses. Compare:

  • With a standard 35mm macro, I can frame first and then adjust focus which only changes framing very slightly with.
  • With the MP-E 65mm changing focus completely changes framing.

Assuming that the angle of view corresponds to a 65mm lens at 1X magnification, it seems that by 5X, the angle of view is about that of a 325mm lens! In other words, manual focusing (this lens does not autofocus at all) looks like it has the same effect as zooming on a zoom lens with the plane of focus fixed at the closest focus-distance.

So why is this not called a MP-E 65-325mm instead of simply 65mm? More importantly, what does the 65mm focal-length represent? And how can I use that to frame by shots with less guesswork?

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I'm pretty sure it's still 65mm lens no matter what magnification you set it to. You are seeing an effective change in the FOV, but the focal length remains the same. I may be wrong, but I'll be interested to see what others say about this as the MP-E 65 is on my list of lenses I'd love to own. – Mike Mar 18 '12 at 22:49
This is a loaner that I've had for a few days and my wife already wants to buy it and a new camera for it :) It's quite amazing and unique. I'll expect have a report on the blog in early April. – Itai Mar 18 '12 at 22:53
The title is misleading or confused. One frames the shot with the viewfinder or LCD screen on the back of the camera, not looking at the focal length. – Pat Farrell Mar 22 '12 at 16:10

1 Answer

up vote 6 down vote accepted

It's called a 65mm because that's the combined focal length (light bending ability) of the lens elements. The focusing mechanism on the MPE-65 works like a set of bellows, i.e. it just moves the whole lens back and forth. You can see this as the physical length of the lens barrel changes significantly when focusing. This has the effect of changing both the minimum focus distance and the angle of view, however the focal length of the lens elements remains unchanged.

It's common for prime lenses change field of view slightly on focusing, the effect is just exaggerated with the MPE-65. Lots of rules break down when you get into macro and super-macro photography, focal length, f-stop etc. cease to matter as the formulas for things like depth of field and exposure don't give accurate answers at macro distances. You have to ignore what it says on the lens and use your judgement or trial an error to begin with.

Note it's standard practice to state the focal length of a lens when focussed at infinity (to account for minor variations as mentioned above). As the MPE-65 doesn't focus to infinity I assume they measure it for the 1x setting, so the value is not directly comparable with other lenses.

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This is as good a guess as we can get without a Canon engineer confirming and makes a lot of sense. Thanks! – Itai Mar 22 '12 at 2:53

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