Originally posted by pcarfan Thank you. I understand it now.

I was thinking all along the focus distance to be the only indicator of how close one can get to the subject, obviously the magnification matter also.

So, a lens that focus as close as 10cm with 1:2 macro will show the same close up detail as a lens that can focus only to 20cm but 1:1 macro, right ? So, it is always a combination of the two.

No. The magnification ratio refers to the original linear dimensions of the subject, so a one-inch worm will be reproduced as a one inch long image if you are using a 1:1 lens at its closest focus distance, and as half-inch if you are using a 1:2 lens at its closest focus distance, regardless of what that distance may be (it could be 10 cm for the 1:2, and 20 cm for the 1:1).

Quote: Also, another related question...how will the dof work in the above example. The lens that is at 20cm and 1:1 macro will have a narrower dof compared to one that can focus as close as 10cm but 1:2 macro, or is it ?...if this is true I'll take the closer focusing lens with 1:2 as I would want a wider dof.

Thanks

As a general rule, yes, depth of focus will increase with focus distance, so a lens focusing at 10 cm will have a shallower dof than a lens focusing at 20 cm, but decrease even more pronouncedly with longer focal length (which you will need to achieve higher magnification at further distances). There are

calculators to figure this out, but for instance in your case, you could have something like a 200 mm 1:1 macro lens focusing at 50 cm at f/16, which will have a dof of 0.24 cm (on a K20D), vs a 50 mm 1:2 lens also at f/16 focusing at 25 cm, for which the dof will be 1.28 cm.

But depth of focus is not the only consideration in choosing a macro lens. If you want to take pictures of bugs, for instance, it can often be a problem to get very close, and you may be better off with a longer lens.