Originally posted by Frogfish ....

Also note though that the DoF when you have a Raynox on IS different to a macro lense alone, it is far shallower.....

In theory at least there is no difference between DoF for a close-up lens approach to macro (like the Raynox) and a dedicated Macro lens if one takes f-number changes into account.

This is because adding a closeup lens to a primary lens changes the focal length of the combined lenses; in effect it make a "new" lens of shorter focal length. This "new" lens is the same distance from the sensor as the original lens, but since it has a shorter focal length, its image is larger (by the ratio of focal lengths.) Because it has a shorter focal length, its f-number is increased in the inverse ratio of focal lengths.

Consider a lens of 100mm focal length focused at infinity, f-number=4. Adding a 100mm close-up lens to the original makes a "new" lens of focal length 50mm, f-number=2, magnification ratio 1:1. The DoF is exactly the same as that of any 50mm macro lens at 1:1 magnification ratio set at nominal f:2.

I guess you could say that since the "new" lens has a lower f-number than the original 100mm lens, it has less DoF (than something - what?) but I think this is misleading as it is indeed a new lens.

What I mean by "no different" is inherent in the DoF equation for macro work:

DoF=2CN(1+1/m)/m

*where C=Circle of Confusion", N = F-Number, and m = magnification.*
This equation doesn't care if the lens in use is a "macro" lens or a construction of other lenses.