DOF question (MPE)

Right, hello ladies and gents of the Macro Sub-forum on POTN!
First off a photo:
http://www.flickr.com …hmuck/468391572​2/sizes/l/
In this shot the DOF nearing the back of the subject quickly, and quite quickly I say, goes to blur.
I was wondering about the cause of this (if not just how the lens works) or if it has a name for that sudden drop in focus that makes it seem like it is exiting a barrier of some kind.

DOF depends on the focus distance so of course it is razor thin at macro distances.

It's just the DOF you get at high magnification with any lens.
see this page for explanation http://liewwk-macro.blogspot.com …d-dof-you-have-while.html.
Brian v.

I do see what you mean and there is another possible explination for that sudden line of sharp to blurry that you can sometimes see in highmagnification macro work (which might or might not use the MPE)
And that is that it is the result of focus stacking where the stacked shots run out of infocus elements and thus the shot moves quickly into blur. I don't think the shot you linked to is a focus stacked shot, the depth of field looks a little thin (maybe) but its dancing right on the cusp.
If you want a more indepth explination, examples and a solution have a read of the following tread by John Hallmen.
http://www.flickr.com …s/johnhallmen/4​504807423/

i would try this at different apertures to see how it changes.
for the kind of work i do f22 is quite useful

I tend to avoid f22 and generally only ever go as small as f16 on very rare occasions.
Have a look at the test shots in this set here:
http://www.flickr.com …4/sets/72157623​350445656/
and you can see as the aperture gets smaller the resulting images start to get a little softer - plus as the magnification increases you quickly have to start using wider and wider apertures to keep the sharpness (partly this is because the effective apertures have infact changed as part of the lenses construction and method of getting to the higher magnifications).

This is effectivly the work of diffraction and I think its a quick test that, whilst not terribly exciting, one can do in an evening and get an idea of the techincal limits of the lens and camera together. For some people f22 is fine for their desired level of quality and output - for others they might not want to close down that far and lose the overall detail and sharpness.

alrighty, just seeing if it had a different name then anything else.