Here is the surgery that I promised to describe:Nikon 40X NA 0.80 M Plan apochromat
It required some surgery, which I will describe separately
I was not able to unscrew the BD illumination collar, so I simply cut it off with a diamond blade in a rotary tool. Macrero showed a similar approach , but I opted to cut off the minimum needed to get a clear light path, while leaving the objective protected by spring loading.
Here is the objective in its pre-surgical state.
The objective gives nominal 0.7 mm working distance. I measure 0.62 mm, using a couple of pieces of aluminum foil and an ohmmeter to detect physical contact.
Here is what the small WD looks like in use, just with the diffuser pulled back.
Setup with this small WD is greatly simplified because many years ago I had bought a 40X NA 0.5 ELWD objective that has the same mount and is parfocal with the NA 0.80. The ELWD gives 9.8 mm WD, so it's simple enough to focus and frame using that, set a hard stop, then back off, switch objectives, advance to the same stop and tweak framing. Without the matching ELWD to set focus and framing at 9.8 mm, working with the 0.62 mm WD would be a lot more challenging.
Just for completeness, here's the overall setup that I used to shoot the cuticle. The hardwired 580EX II provides second curtain sync to use with a long shutter-open time when extra low vibration is needed, with the YN460-II's optically slaved. For the stack shown above, the extra stability was not needed, so I used a 1/200 second shutter time which allowed to leave on the continuous illumination that I had used for setup. According to the setup photo, power setting was 1/16 on the 580EX II, and 1/32 on each of the YN460's.
I hope this is helpful.