Calculating MAG & DOF when stacking lenses

I sure thought that I remembered there being info regarding calculating magnification and DOF when stacking lenses --- but, a search of this forum didn't turn up anything.

I have a Canon 100mm f2.8 Macro conventionally mounted to the 50D, and using a Minolta MD Rokkor-X, full-manual, 50mm f1.4 reverse mounted to the front of the 100mm.

Magnification appears to be approx. 2:1 (determined by viewing mm ruler), DOF doesn't appear to be much greater than 1mm, with both lenses wide-open (again by viewing ruler). Still, it would be nice to be able to calculate, especially DOF, for working a focusing rail.

I do note that I will suffer serious vignetting if I do even the slightest stop-down of the Minolta.

Haven't shot anything with this combo yet, will be searching around for some suitable subjects.

AtDhVaAnNkCsE

I came across this site a while ago and you might find what you need there:
http://home.comcast.ne​t/~NikonD70/index.htm

http://home.comcast.ne​t …e_Close-up_Calculator.htm

I've not the know how nor enough gear to test the theories and the math to know if its accurate or not, so its a case of trusting the site.

GJim,
The max mag with that setup will be about 2:1, by normal calculation it would be 1.5:1 but this does not account for the shortening of the focal length of macro lenses when at min focus distance.
For DOF see http://liewwk-macro.blogspot.com …d-dof-you-have-while.html
You just need to know the magnification and set aperture.
Brian V.

Thanks , I bookmarked
http://liewwk-macro.blogspot.com/200​...ave-while.html
under macro and DOF .
By the way , I did get the 2X m42 and I found and bought an m42 3x also .
Read these and that will make more sense .
http://www.fredmiranda​.com/forum/topic/92795​2
Some great DOF shots . - just keep reading till you get to the DOF ones .