Before the rush

Before the rush
by evan-pak

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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?

share|improve this question
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
up vote 11 down vote accepted

It's called a 65mm because that's the combined focal length (light bending ability) of the elements that make up the lens in its default configuration.

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 use approximations that assume the distance from subject to camera is much greater than the distance from lens to film plane, which isn't the case with macro. 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 focused 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.

share|improve this answer
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
The MP-E 65mm 1-5x Macro does not work like a bellows. The elements in the rear group remain a constant distance from the rear flange and do not move forward with the rest of the elements when the lens is extended.… – Michael Clark Jun 15 '14 at 17:29
@MichaelClark very interesting I'd not seen an example of the how the focusing mechanism works in that lens before. I've updated the answer accordingly. – Matt Grum Jun 17 '14 at 8:44

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