Repurposing fluorescence attachment for visible light epi-illumination?

[littlejackal]

I've been reading a little about incident light microscopy and am somewhat entertained by the idea of being able to examine opaque items such as microchip wafers, etc. The project scope I have coming in the mail has a zeiss fluorescence module minus lighthouse. To my untrained eye it looks as if it might be possible to repurpose this with a bespoke custom-adapted LED module to provide illumination for reflected light microscopy and accomplish the above, assuming all the optics and beamsplitting is in good shape. Unless I am fundamentally mistaken, this attachment would have preformed much the same function only for UV fluorescence.

A stereo microscope might obviously be a better fit for opaque items but we work with the tools we have and this isn't a high priority. If this is a fool's errand I'm happy to be corrected, otherwise I think I'll toss it on the pile of possibilities for future projects.

[Hobbyst46]

A reflected light compound microscope lacks important features of the stereo microscope (working distance to start with).
An epi-fluorescence microscope will easily serve as a reflected light microscope. A high pressure mercury or xenon lamp, however, is unsuitable for reflected light (too bright, UV emission, heat and other issues). So one needs to replace it with either a halogen lamp or LED. An original halogen lamp will provide Kohler illumination as well. A LED - maybe, if small enough and correctly located (distance to apertures and collector lenses).
A "cube" for reflected white light is essentially just a single component - a beamsplitter. No need for dichroic mirror. So the optics of the fluorescence unit can be easily adapted.
We remember though that the thread of fluorescence objectives is (at least on old models) RMS, the same as brightfield objectives, whereas the thread of many epi-objectives is M25.

[littlejackal]

Thanks, Hobbyst46! It sounds like while the component I have might be suitable to jury-rig an epi setup, I will run into the other logistical issues you mentioned. I was hoping that with a swappable turret I could dual-purpose this for both biologic and epi/metallurgy optics but it might be suitable in the long run to just buy something more specialized for the task at hand.

In any event, I’ll continue to read and as I’m still assembling the scope for transmitted light first and foremost it’ll just be an interesting research topic

Thanks for the guidance!

[eKretz2]

I have a BX40 that came with a fluorescence illuminator. It uses cubes in a turret, and works just fine for EPI brightfield and darkfield with the proper cubes and a flashlight stuck in the tube where the mercury burner used to be. So I'd say yes, should be readily doable.

[Hobbyst46]

Most welcome.
Would be nice to see photos of the microscope when you have it.

[Adam Long]

I've got the Epi attachment for my Universal. I've see a few variations available for both the big stands and the standards.

The main variation seems to be whether the beam splitter is in a removable insert - some are not. As mentioned above some turrets have 24mm threads and others RMS. Mine doesn't have a turret at all, just a dovetail for quick-change rings which I have in both sizes.

Zeiss definitely made different inserts for visible epi (labelled H or H-POL) and fluorescence. My understanding is that the FLO beam splitters preferentially reflect UV and pass longer wavelengths - so more UV reaches the specimen but less reaches the eyepiece. My H-POL insert gives a pink cast without crossed polarisers which suggests it is doing some filtering of the blue end of the spectrum too. Apart from the filters and bulb the devices appear to be similar otherwise.

Bear in mind in Epi the locations of the field and aperture diaphragms are reversed.

[littlejackal]

Thanks Adam, eKretz,

I'm piecing together and studying the part sheets for the Standard line and it doesn't look like tugging this EPI thread might be particularly worth pulling. My ideal use case here would be to decap various microchips and examine the dies at magnification which may be outside of that which a stereomicroscope can provide, though I'm just ballparking that requirement. The Zeiss seems like it can be set up for metallurgical or opaque inspection but it would require cobbling together a system that isn't quite as interchangeable-on-the-fly as I'd hoped. I'm seeing the same single-objective vertical illumination turret which I suppose could be considered interchangeable given that I'd probably need to exchange the objective turret from biologic objectives anyway.

I'm saying this with remarkably little prior research into the optics of a microscope beyond what I've managed to absorb in a few days, but my target was a scope that would have the vertical illuminator fixed in place on the neck, an LED (or genuine visible light lamp) fixed to the right spot to aid in kohler illumination, and a turret which would swap based on what I intended to view at any given moment, whether it's transmitted light samples or opaque specimens. So the challenges I see right now are:

- Obtaining an insert for the VI, be it H-POL or whatever else is suitable
- Obtaining epi objectives, presumably because biologic objectives are unsuitable for this lightpath. Not sure if they're entirely unsuitable (will work in a pinch, it'll just look awful) or entirely unsuitable (doesn't work, you won't see anything)
- Fitting EPI objectives to turret - obviously RMS vs 24mm would be a non-starter for the current replaceable turret, not sure if attempting to 3d print an insert to try with a for-parts 4pos turret would be doable, but I strongly suspect there's more optics at play here that would make it impractical

or alternately just source the dedicated metallurgic vertical illuminator for the Standard line, live with the single objective swap limitation.

The second seems more practical if I ever did decide to go that route. Perhaps in future I might look at building a dedicated EPI metallurgical Standard, though at this point it seems there may be better platforms to build on, even if I am addicted to the Zeiss look

Thank you everyone for checking my thoughts on this. Since I'm new to the hobby I'm doing a lot of drinking from the firehose of information, and as a result there's a big aspect of "run before you can walk" happening. I see the possibilities of what I CAN do with a microscope and I'm trying to do them all to some extent. I'm not rushing out to buy any additional scopes right now and want to get my transmitted light legs under me, but with an eye for future experimentation

edit: I'll certainly post my Zeiss setup(s) once they're more than just a bare base. I do have a few things to do to the bases as they are -- very gummy, dried grease, so I'll for sure be asking for advice on cleaning once I've sorted through all the available information so I'm not asking duplicates

[Greg Howald]

I have a metallurgical scope with an epi lighting system that uses a 30w halogen lamp. Lowest objective is 2x and highest is 50. Some times the image seems hazy. If I lower the intensity of the bulb it yellows pretty readily. Much of the time I get better imaging if I use a black or white background on the stage. This helps eliminate added reflection. I do often wonder if it would do better with an LED lamp but I lack the knowledge or understanding of how to change it. I have a 50w bulb but I'm afraid that would be far too hot. So I feel like I'm stuck with what I have. Suggestions would be welcome.
Greg

[eKretz2]

I also have a Vanox AHMT and it runs a 100W halogen bulb in the base, but it has dual cooling fans that run as soon as the scope is turned on. I recently bought some COB LEDs to try out, have tested one and it does pretty good - also eliminates the need for the blue filter that is often necessary for the halogen bulb. I use all sorts of different backgrounds with EPI. Sometimes black, sometimes white, sometimes even a mirror. It's good to try different things.

[Greg Howald]

I have used a mirror also. Sometimes it is very helpful.
I also do other colors and polarization.