B A quartet of epi-illumination methods

[Andy Resnick]

TL;DR Summary

I finally obtained a set of epi-phase microscope objectives (Zeiss)

Well, it took almost 20 years (!!!), but I finally obtained a set of epi-phase microscope objectives (Zeiss). The principles of epi-phase contrast is nearly identical to transillumination phase contrast, but the phase ring is a 1/8 wave retarder rather than a 1/4 wave retarder (because with epi-illumination, the light passes through the ring twice). This method was popular only for a very short period of time before epi-DIC (differential interference contrast) became widely available. So, not only are epi-Ph lenses impossible to find, but they are cheap because nobody wants them :)

Here are 4 images of a razorblade comparing the different epi illumination methods, all using 40x lenses. In order: brightfield, phase contrast, DIC, and darkfield:

While epi-phase looks a bit like epi-darkfield, the biggest difference is the light throughput- 1/30 s shutter (phase) instead of 5 s (darkfield).

Success! I feel like Captain Ahab, if he had finally caught Moby Dick. But I guess that would moot the point of the story....

 

[sophiecentaur]

TL;DR Summary: I finally obtained a set of epi-phase microscope objectives (Zeiss)

but they are cheap because nobody wants them :)

II that 'cheap' like a second hand Maserati or cheap cheap? Captain Ahab went overboard , remember so be careful.

I guess they need all you existing gear to do their stuff. I'm pleased for you and the images are interesting. Could you do labels?

 

[Andy Resnick]

II that 'cheap' like a second hand Maserati or cheap cheap? Captain Ahab went overboard , remember so be careful.

I guess they need all you existing gear to do their stuff. I'm pleased for you and the images are interesting. Could you do labels?

cheap-cheap: Including shipping from Europe, the cost was $US 120 for all three, all in new condition, likely never used :)

Thanks, re: the images. More to come as I improve my technique!

 

[Andy Resnick]

I'm starting to get the hang of it; in microscopy (unlike astronomy), the photographer must prepare their own objects to photograph. Epi-phase works best on extremely flat surfaces (polished metal, for example... or computer chips), and here's what I was able to produce: all images are JPG straight off the camera, no post-processing/photoshop/etc. The first image is epi-brightfield, the second epi-phase.

First, an overprocessed CCD array:

Epi-Phase contrast works by using 2 filters to cause specularly reflected light to destructively interfere with itself, so that the image intensity is proportional to the phase difference between "scattered" and "unscattered" reflected light. (I don't know better terminology). The colors here are most likely from thin-film interference created by multiple transparent layers.

And next, another IC but completely "blank" (obviously there's something going on underneath the opaque layer):

Here, epi-phase clearly shows the topography of the top layer. This image also shows how unforgiving the technique is for (ahem) dirty optics (see the dark rings along the right side) and misaligned components anywhere in the entire optical path (uneven illumination).

Also- if anyone can identify that cryptic logo (not the year or copyright symbol, duh....) on the second set of images, I'd appreciate it!