Hmmm...my Vivitar Series 1 90mm f2.5 macro is over 30 years old and has traveled around the world and operated under all types of challenging field conditions....my daughter still uses this lens,the Vivitar 135mm f2.8 macro and a few other MF micros and doesn't have any problem either,using them for the challenging field conditions of marine biology,as well as the lab.
It's a matter of your technique and what you're used to. When I shoot between 1:2 and 2:1 macro (with tubes), I'm almost exclusively between f/8 and f/16. I think everyone would agree that focusing wide open is the only usable option here. I tend to shoot handheld a lot, often with flash.
For this technique, I "hover fowards and backwards" to focus and when I find focus I hit the shutter.
If you shoot on a tripod (in a lab) or at wide enough apertures to focus with, it's much easier to either focus stopped down slightly or keep turning the aperture ring, but for my technique it's really a must to focus wide open and only stop down when the subject either does something I'm waiting for or when the critical focus is achieved. Manual Focus is perfect for macro, but manual aperture isn't for everybody and is certainly not always usable. I think that's something a potential new user should realize.
