What is special about macro lenses?

Started Aug 10, 2005 | Discussions thread
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crazypea Regular Member • Posts: 176
What is special about macro lenses?

One of my next big purchases will be a dedicated macro and while I have used macros extensively, I can't find a good online tutorial that explains what makes them special. Can any of you please help me out?

As near as I can tell, they are "optimized" for close-focussing to create life-size image reproductions on the sensor. This is achieved through intermediate floating optics (an extra moving group in the lens) that shorten the working distance while minimizing aberrations (spherical, I assume). I've also heard that macros have a flatter image plane than normal lenses (reduced sperical aberration), which I have taken to mean that they use less of the image circle, i.e. there is less focus fall-off towards the corners.

I also have a Minolta Dimage 7i that has a macro mode. When I flip the macro switch, I hear a whirring as if a lens group is moving to a new position. Is this indeed what is happening? This seems vaguely consistent with what I wrote above. I also have a Sigma 28-80 (for my DS) that does macro at 80mm. How does this lens work? Does the macro switch engage a new gear that moves an additional group instead of just the primary groups?

Is any of this correct? Are there bits and pieces that you could fill in? I'd love to learn a bit about the optics/mechanics if you can write back, or point me to a good site.

I have a background in optics, but have never known much about camera optics, or specific designs for specialized purposes. Any information that you can offer is greatly appreciated!

Best wishes,
Adrian

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