All else =, will a >focal length Macro have >DOF

I am working with an EF 60s and and I do understand that macros in general have very limited depth of field but was wondering if moving from a 60mm to 100mm would increase that depth if everything else was equal such that I'm shooting the same size final object in the image. I'm fine with the working distance and everything else but wasn't sure how the DoF related to focal length. Any insights?

All else being equal the longer focal length will result in less DoF.

If you are shooting at 1:1 it doesn't matter wether you are using 60mm, 100mm or 180mm macro lenses, the DOF will be identical only the working distance will change.

Though this is not exactly true because of the nature of lens designs-floating element macro lens optics-the biggest two effects of going to a longer focal length macro are:
1. As mentioned, Working Distance (lens front element to subject distance) does increase significantly as focal length increases, out to about 200mm.
2. The macro out-of-focus image background gets "more absolutely blurred"- more pleasingly blurred-as focal length increases.

So, no, moving to a longer macro will not increase DoF appreciably, unless you frame the image differently.
DoF is a mathematical concept, because it depends on circle of confusion and viewing distance, as much as it depends on a subject distance/lens focal length. So, for all practical purposes, if you are happy with the excellent EF-S 60mm, then:

1. Carry more light with you, carry flash, carry reflectors, and/or use longer exposures so you can increase the Aperture to f/16+. I have shot this lens at f/22+, and the DoF gain exceeds the diffraction loss of sharpness. Not only does flash allow you to use f/16, but the flash will "freeze" motion blur at lower shutter speeds when the flash is a dominant light source.
2. Pay close attention to the angle the camera is pointed relative to the plane of focus on the subject where you want the maximum DoF to be.
3. Use a smaller APS-C sensor camera. The Rebels/20D/30D have more DoF than larger sensor cameras like the 1-D or 35mm.
4. Try and get the background of your image separated, to be further away from the foreground subject. Then the perception of blur background to sharper foreground will give viewers a better impression, even if your DoF in compromised.

Jack

Thanks all, I appreciate the discussion. I'll stick with my 60mm as I'm pretty happy with the overall results.

At macro distances all that matters is the magnification, the depth of field will be more or less the same for the same magnification.

There is a lens specific difference due to a parameter called the pupilary magnification which is related to if the lens is a telephoto or a retrofocus construction.

The equations are here.

Things are more complex with internal focus lens designs as the pupilary magnification will change with focus distance (magnification).

In the case of your transition from 60 to 100mm then presumably the pupilary magnification P will get smaller with the 100mm as the lens should be "more telephoto" in construction.

Assuming at life size (M=1) for the 60mm P=0.8 then at f16 dof=1.37mm, and similarly assuming at life size P=0.3 for the 100mm then again at f16 dof=1.64mm.

However, I am not sure exactly of what P is for the 60mm as I don't have one (the link explains how to measure it).

Here is a table for the 100mm:
M ---------- P
0.0000 0.7333
0.2000 0.7333
0.3333 0.7000
0.5000 0.6000
0.6667 0.5161
1.0000 0.3243