A quartet of epi-illumination methods

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SUMMARY

The discussion centers on the acquisition of a set of epi-phase microscope objectives from Zeiss, which utilize a 1/8 wave retarder for phase contrast imaging. Despite their historical significance, these objectives are now largely overlooked in favor of epi-DIC (differential interference contrast) methods, resulting in their low demand and affordability, costing only $120 for three lenses. The user shares insights on the imaging capabilities of epi-phase contrast, particularly its effectiveness on flat surfaces like polished metal and computer chips, while also highlighting the technique's sensitivity to optical cleanliness and alignment.

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  • Understanding of microscopy techniques, specifically epi-illumination methods
  • Familiarity with phase contrast and differential interference contrast (DIC) principles
  • Knowledge of optical components, including phase rings and filters
  • Experience in preparing and photographing microscopic samples
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  • Research the differences between epi-phase contrast and epi-DIC microscopy
  • Explore techniques for improving optical cleanliness in microscopy
  • Learn about the effects of thin-film interference in microscopy imaging
  • Investigate the best practices for preparing samples for microscopy photography
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Microscopists, optical engineers, and researchers interested in advanced imaging techniques and the historical context of microscopy methods.

Andy Resnick
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TL;DR
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:

DSC_7951 copy.webp



DSC_7952 copy.webp


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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....
 
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Andy Resnick said:
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?
:thumbup:
 
sophiecentaur said:
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?
:thumbup:
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!
 
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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:

DSC_8567.webp


DSC_8568.webp


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):

DSC_9063.webp


DSC_9065.webp


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!
 
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