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The Canon EF-S 60mm f/2.8 Macro USM Lens loses 1/2 stop at 1:5, 1 stop at 1:3, 1.5 stops at 1:1.5 and 2 stops at 1:1 (lifesize).

Can anyone confirm that at 1:5 magnification, the Canon EF-S 60mm f/2.8 USM lens has a maximum aperture of f/3.4, at 1:3 magnification the maximum aperture is f/4.0, at 1:1.5 it is f/4.8 and anything below that is f/5.6?

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up vote 3 down vote accepted

My Nikon 105mm drops from f/2.8 to f/4.5 at closest focus, so that sounds right.

A post at betterfamilyphotos has a post where they say (emphasis mine):

You would imagine that using a macro lens is the same as using a normal lens, and you would be right except that with a macro lens when you get close to 1x magnification, you start losing light. My 60mm for example starts losing light at close ranges until it reaches 2 stops of light loss at 1x magnification, this means that the effective aperture is f/5.6 instead of f/2.8 (regarding light quantity entering, not DoF). If you are using auto modes on the camera like aperture priority or using flash in TTL mode then the camera will auto compensate for the light loss, but if you're metering light manually you need to take it into account, Canon has included a table in the user manual with the light loss values at each magnification level.

So if you have access to the manual for this lens, or request one from Canon, it should verify the information. It's expected for a close focusing macro to lose 1-2 stops.

The above post is incorrect, however, in saying that the reduction in aperture doesn't affect DOF. It does. Two references for those interested in the physics of it:

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So you're saying it is only the equivalent f-stop loss of light, not increased DOF. So explicitly setting the f-stop to f/5.6 would keep the same light in, but also increase the DOF? – Nick Feb 16 '12 at 8:47
No, the f-stop loss increases DOF (the blog post referenced above is incorrect on that point), and if you are at f/5.6 to start with, focused at infinity, then at 1:1 you will be at f/11. I'll edit the answer with additional references. – MikeW Feb 16 '12 at 9:13
Thanks for clarifying the DOF issue. So the camera is unable to display the 'effective f-stop'. In your example, it displays f/5.6, although it is effectively at f/11. Seems like a camera limitation, unless there are models that correctly adjust the max aperture, similar to what happens with variable aperture zoom lenses as you approach the maximum focal distance. – Nick Feb 16 '12 at 9:30
My D90 does change from f/2.8 to f/4.5 as you focus, but if you start it above f/4.5 it remains fixed. I'm not sure why, unless it compensates by opening the aperture as magnification increases to match the focal length (something it can't do when it's already at max aperture, starting at f/2.8) – MikeW Feb 16 '12 at 10:10
Interesting... I have read earlier that Nokia cameras show the effective aperture during focus -- auto aperture compensation is also quite impressive. Maybe what it does is prepare the shot for f/2.8 to simulate the f/4.5 that you explicitly requested. 10x again for all the info -- very hard to find ppl that can assist w/ this sort of info. Much appreciated! – Nick Feb 16 '12 at 12:08

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