Building a phase plate is tricky business. First part is the material. Mica is easy enough to find, but getting just the right thickness and a uniform surface is less straightforward than you might imagine, even though it does cleave neatly into sheets.
I tried to think of many ways to cut a neat ring, from hole punches, to lathe cutting, to die-cutting and finally resorted to these cheap annular punches. I think a better solution would be to get some wave plate film and use a cutting plotter such as a cricut machine so that you could try out different sizes easily. The punches work OK, but introduce some distortion while cutting and are somewhat difficult to obtain concentricity with. I cleaned this one up a little before mounting.
Voila. The punches are in the background. I used a broken coverslip as the mounting plate. Static electricity held the ring on pretty well. This was a 10x achromat objective so this is actually pretty close to the back focal plane of this one. Believe it or not, some phase contrast was acheived with this one. It's not exactly a quarter wave, and there was not very much amplitude dimming, also the wave plate itself scattered some light, but the phase was there I tell you! You got to believe me!!
Anyway, if you've never used real phase contrast before, I would give it a try. It's great, and pictures alone don't really capture how much the contrast twinkles and catches the eye. I was lucky enough to find what appears to be a complete B&L set, the early one with annular filters rather than a turret. It's really a fantastic set, with a low NA centerable condenser with the giant filter slot, phase achromats in 10x, 21x, 43x, a green Kodak filter, and even the telescope:
I hadn't seen one before this, so here it is for reference. If you like to fiddle with settings a lot, using this set with a mirror and separate illuminator is the best.
damn overexposed!
I would say that the filter doesn't really help a whole lot for three reasons, 1: the 50s-60s era B&L achromats are pretty darn good 2: I am already using a much cooler, green light heavy LED lamp than the halogens or whatever that this set had in mind and 3: there isn't really a lot of color to begin with in these samples.
