Microscope EPI dual illumination (flash and halogen)

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Bugeyes
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Microscope EPI dual illumination (flash and halogen)

Post by Bugeyes »

I've searched the forums looking for a similar question but have been unsuccessful, so I'm posting this idea for feedback and critique. Apologies if this has been already covered in some post.

I have an EPI (reflected light) microscope with a 30W bulb and I want to use flash for my stacking while, perhaps, improving my focusing light as well. I've concocted a scheme that I think will work and bypass the need to change the setup when switching between the halogen light (for focusing) and flash (for the stacks.) I'd like to know if there is any reason this setup won't work. Below is a block diagram (note: in PLAN view) of how I'm going to use another, old EPI cube (in its housing) to effect this.
Image
This "old" (Ebay acquired) EPI housing should allow me to have light inputs (flash and halogen) at 90-degrees, always fixed in place, without crowding. There will be some illumination loss due to the half-silvered mirror but I am confident I can get enough flash for exposure and I plan on using a 150W "gooseneck" halogen light for focusing, which should be an improvement even considering light losses. By turning the old EPI-housing on its side and using the output from the "objective direction" as the entry point (current 30W bulb position) to my current EPI tube, I should be able to accomplish my goal. In the diagram the orange colored light normally would flow the other way where the blue colored light is following the path it normally would through the cube. I've disassembled my current 30W lamp housing and have complete access to the spot that the 30w lamp filament occupies so, while the light won't eminate from a "point", it will enter my current EPI tube at the proper place, geometrically.

Granted, I have a lot of fiddling, rigging, and assembling in my future, but that's half the fun of this hobby, no? But, what might I be missing in this scheme?

Thanks to everyone.

enricosavazzi
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Post by enricosavazzi »

It should work, but besides the unavoidable losses by the beam splitter (probably some 50% for each light path if it is a 50/50 splitter), both light sources will be farther than the original one from the epi illuminator, and out of the focus of any collimator in the epi illuminator.

Unless you need Köhler illumination, even with all losses you may have enough light left (especially from the flash).

It is probably not worth the effort of mounting collimators of the right focal lengths between each light source and the beam splitter, unless you want Köhler illumination. Once you do achieve proper Köhler with collimators, the light intensity might even be lesser than without.
--ES

Pau
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Post by Pau »

enricosavazzi wrote:...both light sources will be farther than the original one from the epi illuminator, and out of the focus of any collimator in the epi illuminator....

...Unless you need Köhler illumination...
You're right, the main issue is the optical position of the light sources far away of the original light source.
The only epiilluminator I have is for epifluorescence and Köhler illumination is absolutely needed with it.
For transmitted illumination I use a similar DIY scheme, fortunately the collimator optics are focusable and I also can get Köhler
Some links:
http://www.photomacrography.net/forum/v ... hp?t=26185
http://www.photomacrography.net/forum/v ... 404#161404
http://www.photomacrography.net/forum/v ... 611#224611
Pau

ChrisR
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Post by ChrisR »

I query the choice of a gooseneck light source. I appreciate that it's something you have and it works, but designing from scratch, isn't an LED more attractive?
Chris R

iconoclastica
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Post by iconoclastica »

ChrisR wrote:I query the choice of a gooseneck light source. I appreciate that it's something you have and it works, but designing from scratch, isn't an LED more attractive?
I have been experimenting with that. In a defunct cold light source with two goosenex, I placed a motor cycle headlight (LED, 20W) and a collector lens. It was not nearly bright enough. Used with an m-plan 60x I had to expose 8 sec and still had a dark picture. Through the eye glasses I could see hardly anything.
--- felix filicis ---

Saul
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Post by Saul »

iconoclastica wrote:
ChrisR wrote:I query the choice of a gooseneck light source. I appreciate that it's something you have and it works, but designing from scratch, isn't an LED more attractive?
I have been experimenting with that. In a defunct cold light source with two goosenex, I placed a motor cycle headlight (LED, 20W) and a collector lens. It was not nearly bright enough. Used with an m-plan 60x I had to expose 8 sec and still had a dark picture. Through the eye glasses I could see hardly anything.
You have to place the LED close to the FO entrance ( I suspect you used big size LED also - it should be smaller, with smaller angle of the emission).
My experience with the Scienscope fiber optic light
No problem at 50x (do not own 60x)

iconoclastica
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Post by iconoclastica »

Saul wrote:You have to place the LED close to the FO entrance ( I suspect you used big size LED also - it should be smaller, with smaller angle of the emission).
My experience with the Scienscope fiber optic light
No problem at 50x (do not own 60x)
OK, going to read that. Only by moving the lamp back and forward and doing the same with the 50mm lens, I got the best output by focusing the lens on the fibers' base (as judged by eye).

What a wondrous thing, that other people found the same use for a motor cycle light!

---------------------------

EDIT: since we are creeping off topic, I placed my findings here.
--- felix filicis ---

Greenfields
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Post by Greenfields »

Interesting idea.

If you try it please let us know how well it works

In case it helps:

Kohler illumination is used in vertical illuminators just as in sub-stage illuminators.

The aim is to do the same three key things as with transmitted light:

a] To capture as much light from the source as possible using a short focal-length, typically aspheric collecting lens or group. The collector group may be part of the lamphouse and emit an approximately collimated beam.

b] To completely defocus the source in the plane of the specimen so that no trace of any structure in the source [e.g. the filament of a halogen lamp] is superimposed on the image of the specimen. Just as in conventional Kohler illumination this is done by focussing an image of the source in the plane of the rear pupil of the objective.

c] Magnify the source so its image is large enough to fill the rear pupil of the objective. Low magnification objectives tend to have the largest rear pupils though that is less true of modern high n.a. objective designs.

The collimated beam from the lamphouse is usually focussed as an aerial image of the source in the plane of an adjustable iris - the aperture stop - inside the horizontal arm of the vertical illuminator. This arm also includes field stop in the conjugate plane of the image to control the illuminated area of the specimen.

Your question suggests the following thouights:

1 - I assume that currently the end of your fibre optic illuminator has been placed in the position of the original lamp and uses the original lamphouse collector lens. If you still can, check that your lamphouse produced roughly collimated light with the original bulb. If so, that's what the rest of your illuminator will expect.

It if does, it means that the beam splitter could be placed between the lamphouse and the first lens of the horizontal tube. If you move the end of the illuminator further from the collector lens you will mess this up. You can't move the end of the illuminator far from this position without reducing the light collected and spoiling b] and c]

If the fibre-optic illuminator has its own collimator that makes things easier.

2 - You then need to do your best to find a short focal length lens to place in front of the flash unit to approximately collimate the light from that and direct it at the other sinput of the beam splitter.

3 - The magnification of the whole illuminator will have been designed to fill the rear pupil of the range of objectives the manufacturer had in mind with an image of the original lamp filament. I guess that the flash tube will be rather lomger than the filament which will mean that the system will only use a part of the tube about the size of the original lamp filament.

None of this will stop your experiment from being successful if the flash happens to produce enough light to off-set all of the losses.

Henry
Feel free to edit my images.

Bugeyes
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Post by Bugeyes »

Update to this project. No real advance made. As most of you predicted, the loss of light is just too great, since it had to pass through too many splitters and too much glass. Hardware-wise, it made a neat package but really was impractical. I was unable to get an approximation to Kohler illumination, which was no supprise, and contrast suffered. The setup seemed to increase the glare also, although I could get very even illumination. The condensor aperture became almost useless. The moral of the story is that the condensor optics are designed to have its light eminating from a point (or something close like a filament) and simply won't have it any other way! I didn't invest much money but I did spend a fair amount of time on construction. I've leared from this (and previous illumination-improvement projects) that trying to be clever with lighting (with plano-convex lenses, fiber optic cables, etc.) is like chasing moonbeams: you never can catch them. The inverse square law becomes the Law of Diminishing Returns faster than anything you can do to try and get ahead of it. The best strategy is to get whatever light source you are using as small, bright, and close as possible to whatever illumination condensor you are using. Any other strategy always comes in second place WRT any improvement. Thanks to all for suggestions and wisdom.

P.S. I did make one interesting discovery. I purchased a big 50W LED and butted it against an aluminum piece with a 5mm hole in it placed exactly where the halogen filament would have been and was able to "almost" get Kohler illumination. I certainly had a enough light, and nearly blinded myself while assembling and testing the thing. The "pinhole" attempt was more satisfactory than anything else I tried but the setup (with cooling block + fan, etc.) was a real Rube Goldberg (Heath Robinson) affair and impractical for regular use.

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