Found tufuse and tufusepro by Max Lyons. Tried it. It didn't
compensate for FL changes of macro lens as it's focused! It also does
exposure blending, but I haven't tried that yet. tufusepro is free.
Why wouldn't you simply move the camera with respect to the subject
instead of focusing the lens?
That is a most interesting question.
The answer is that usually focusing the lens yields a more pleasing picture. It comes down to two things: stacking performance and perspective. Moving the entire camera as a system causes an enormous perspective shift that decreases stacking performance (increases artifacts like "echos") and flattens perspective: often to a totally flat "orthographic" perspective.
Chuxter shot his image with a 60mm macro (the older edition) of a chunk of circuit board about 50mm (2in) wide (judging by the size of the components) and 50mm deep (judging by the angle he has the board at).
There is a sense of perspective in the image, you can see straight rows of components converging towards center as you move farther back. I rather like that.
That would put the front of the image at about 2x magnification. At 2x, the 60mm f2.8 puts the first subject plane 256.5mm from the sensor plane. Focusing back 50mm farther puts the last subject plane 306.5mm from the sensor. The magnification last plane is 2.95x, hence the pleasant perspective.
Now, here's where it gets interesting: the 60mm f2.8 is a floating element design. The entrance pupil (the "center of perspective") is partially anchored to the rear sections of the lens. As it shifts from 2x to 2.95x, the entrance pupil moves 4.7mm away from the subject. Yes, that's "apocryphal perspective", but it's very slight. There will be magnification correction, but because the entrance pupil moves so little, it will track perspective well.
The end result is going to be very similar to what you would see with bellows draw focusing, locking a "no floating element" macro lens into place, and slowly moving the camera nearer to the lens as you focus back. The perspective comes from the entrance pupil location, about 179mm from the front of that circuit board, or 3.6x the board width away. That's a pretty natural perspective, like looking at a car from 20 feet away.
Moving the camera would result in different perspective possibilities. The magnification would be constant, obviously. Good stacking software gives you the option of compensating for magnification changes. If you stacked with constant magnification, you would have orthographic perspective, a rather flat looking image. Great for technical analysis of the board, horrible as "art".
Allowing the focus stacking software to automatically adjust magnification could result in darn near anything, from nearly orthographic, to near entrance pupil perspective (more like 204 than 199mm, because the entrance pupil shifts all the way from 179mm to 229mm) depending on the algorithm that computes magnification. Yes, your perspective, and therefore your overall image appearance and "feel" has become random: out of your control.
The other big problem with moving the camera is echos. The entrance pupil is shifting. The ratios of sizes of out of focus image components is different in each layer of the stack, even if the magnification adjustment corrects the in-focus components. So, when different slightly OOF planes are chosen based on which one is closest to in-focus, you get "echos", as experienced stackers usually call them, or bands or halos (as has been used in this thread). With over 10x the entrance pupil movement of the "focus by lens" approach, the end result is 10x the echos.
This is exactly the same thing that happens when you keep camera and lens stationary and move the subject on a focusing stage.
So, overall, you have four choices:
1) focus with the lens's control on a floating element lens. Perspective is good for art, there are minimal echos, and magnification must be corrected.
2) focus by moving camera or subject. Maximum echos, and your choice of flat "orthographic" technical perspective or a random perspective.
3) focus with bellows draw (this obviously requires a bellows, ad a good bellows lens). Perspective is good for art, there are no echos, and magnification must be corrected.
4) buy or improvise a telecentric lens. There are no echos, at all. The perspective is flat orthographic and cannot be changed.
wizfaq
--
Rahon Klavanian 1912-2008.
Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.
Ciao! Joseph
http://www.swissarmyfork.com 
