Macro Lens Design

What specifically is different about the design of a Macro-type lens to allow it to focus so much closer than a standard lens?

Not sure how technical an answer you want. The design - arrangement of the internal glass and how it moves during focus.

I would like to know what they mean when they say "Floating Focus Elements" what on earth do you think that does?

Nick

Feel free to get as technical as you'd like and I'll do my best to understand.

Macro lenses obviously focus closer but will also be better corrected for the aberations that increase for normal lenses in close focus, typically chromatic aberation. Macro lenses will normally also have better flatness of field at close focus, important for copy work. Also they are normally optomised for very high sharpness at normal distance so as to maintain good sharpness at higher magnifications.

For example the MP-E 65mm "A floating system preserves optical quality at different focusing distances" aparantly referes to correcting CA over the wide magnification range of the lens and refers to elements that move around inside the lens depenendent on the magnification used. Similar words are seen for the 180mm macro although as this only mangifies to life size it is probably less of an issue.

You can find out more about this sort of termonology and technology if you get the book Canon publish "The Eyes of EOS III" or something.

Lester explained it well with the sentence "better corrected for the aberations that increase for normal lenses in close focus, typically chromatic aberation. Macro lenses will normally also have better flatness of field at close focus" !

Nick_C wrote:
I would like to know what they mean when they say "Floating Focus Elements" what on earth do you think that does?

Nick

Most, if not all, lenses are calibrated to perform at their best when focussed at infinity. Macro shots are never anywhere near infinity and macro lenses have a very large range between their minimum focus distance and infinity.

Floating element groups change their position as the focus element is moved to attempt to compensate for the deviation from the ideal setup. It's a system that has been around for a very long time and works well.

I have to disagree with this, most macro lenses work well, often very well, at infinity and or often used as regular lenses. The obvious exception to this is the MP-E 65mm Macro photo that has a minimum magnification of life size. Lenses like the EF 100mm f2.8 Macro make excelent telephoto lenses.