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PostPosted: Tue Jan 22, 2019 6:56 pm 
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After biding time for more 'n a month now finally the cree-led and its driver have arrrived from China. The mounting of the pair onto the epi-illuminator turned out easier than I had foreseen. I was lucky to find two cardboard tubes that neatly fitted eachother and the entrance of the illuminator. Adding a few rounds of tape made a really snug fit.
An element from an old 50mm m42 lens to be used as collimator lens slid in place like it was made for it. So in about an hour I had my working epi-illumination.

The 10W led is bright enough. At least, without using any filters. Perhaps I am cutting light for one of the tubes ends in a metal cap with a hole in it, that acts like an aperture. Thermal grease is still on its way, so I don't dare to leave it on for long, but it seems that the metal bracked on which I mounted the led transports the heat outside of the tubes.

So, in a quantitative sense, the job has been succesful. Now what about quality? The field aperture works exactly the same as in trans-illumination. So that is clear. I don't know what is best for the other aperture, the one analogous to the one of the condensor in the TI.

Most difficult question: when is the collimator set up correctly? To some extent, I can move the led closer to/further from the collimator lens. That lens has a focal distance of aboutish 50mm. I expect the led ought to be exactly f from the lens to create an afocal bundle of light? How do I know when I have done that?


Last edited by iconoclastica on Tue Jan 22, 2019 10:00 pm, edited 1 time in total.

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PostPosted: Tue Jan 22, 2019 9:32 pm 
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Here's a few photos of the present state.

The rightmost part is taped to the black ring that ends the epi-illuminator. Of slightly reduced diameter, the inner tube is on the left, with the aluminum bracket that carries the LED sticking out:
Image


The inner tube with the bracket. The black box is a relay and the extra wires lead to a push button to make the driver switch modes when the power is briefly interrupted (full power; half power; blinking). For the time being I limit myself to half power.
Image


The LED-contraption mounted on the Labophot (slightly out of focus... sorry :oops:)
Image

Finally the irst picture made with the new illumination:
Attachment:
File comment: stoma of Polypodium australe (dehyrated leaf). Nikon M-Plan 60x epi-illumination
stoma.jpg
stoma.jpg [ 205.7 KiB | Viewed 3900 times ]

The whole setup is still a bit amateurishly, but I won't spend much effort on it until I am convinced the idea is sound.


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PostPosted: Wed Jan 23, 2019 1:32 am 
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Approx what exposure do you need?


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PostPosted: Wed Jan 23, 2019 12:51 pm 
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ChrisR wrote:
Approx what exposure do you need?

I just made a test exposure (details follow) of a piece of white acrylic and let the camera make it mid grey +1. This gave me 1/6th@ISO100, aperture diaphragm wide open, field diaphragm set to fit field, LED half power.

For comparison, in transmission lighting with a piece of crispy plastic bas as target I got 1/13th@ISO100, aperture diaphragm 0.8, field diaphragm set to fit field (slidely wider than the previous due to centering differences), lamp at full power (Labophot 20W halogen).


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PostPosted: Wed Jan 23, 2019 1:34 pm 
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This morning I made a few technical tests with the illuminator. I realized that there ought to be a conjugal image at the position of the aperture diaphragm [AD]. (As an aside: could anyone explain why in reflective köhler the field aperture comes after the AD?). I tried to open the illuminator to place a screen at that position, but it turned out quite hard to do. The tube of the illuminator unscrews in three parts (careful! the aperture blades can become dislodged, so always keep the iris facing up). The AD is not the end of the first part, but the start of the second. It's therefore not feasable to place a disk of paper there and see what's projected.

Instead, I hung a sheet of note paper at a comparable distance after the first (lampside) part of the tube. But first I bent a piece of wire over the led to get a good shadow, for the image of a burning led is featureles and only hurts the eyes. Whith a little adjusting I got this:
Attachment:
File comment: Image of the LED with wire over it, near the aperture diaphragm
_WDW7612.jpg
_WDW7612.jpg [ 125.76 KiB | Viewed 3848 times ]


The image moves forward and backward with contrary movements of the led relative to the collector lens. So, whatever the details, the concept seems sound to me.

Still I don't know how to position it exactly. Next I did the following - I don't know if it makes any sense, but if so, kindly explain me why:
The illuminator, when held in hand, projects a light circle on my desk. By moving it up and down I can get the blades of the FD into focus. This is about 10cm above the desk top, which judged by eye cannot be the back focal plane of the objective. I then adjusted the led position such that together with the iris blades I got the wire shadow in focus too.

With this adjustment I tested the evenness of the illumination. I made a photo of the surface of a piece of white acrylic and then plotted the luminace over the diagonal from top-left to bottom-right. Here's the result (blue line), compared with a similar test using transmtted light:
Attachment:
File comment: Luminance measured of the field diagonal. Blue: epi-illuminator; red: transmitted light.
luminance.jpg
luminance.jpg [ 95.29 KiB | Viewed 3848 times ]


There's about one stop of vignetting towards the cut-off of the FD. It's asymmetric because my camera still is slightly off-centre. Note that I forgot to remove the iron wire...


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PostPosted: Thu Jan 24, 2019 1:19 am 
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That doesn't look too bad?
I guess you could move the led and try again..
Is this the BD illuminator? If so I have one of those too, also without a lamphouse.

Are you sure there's no lens in the lamphouse? I assume there would be a mirror. I'm just thinking where I saw someone had made an LED adaption, he used a very short focus colector lens for his led. Do Nikon produce a drawing , maybe?


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PostPosted: Thu Jan 24, 2019 6:48 pm 
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I am quite satisfied with the results indeed. Today, I removed the metal bottom of the outer tube that had provided me with an unsollicited extra aperture. This resulted in some 30% more light output, if the scale of a photoresistor module is anywhere near linear. And also more freedom to move the led forward and backward, so I can find the exact distance of the brightest output.

That distance is near, but not equal to the one I found yesterday by projecting the filament in focus with the aperture blades. And I was mistaken yesterday, for those blades are the ones of the A-aperture and not as I thought of the F-aperture. The projection plane falls into the proximal parts of the objective.

All this is done with a temporary test set-up in order to determine the paraeters of the long-term lighthouse. I am breaking my head now on how to make the led center-able in three dimensions while connected to a sufficiently large heat sink and keeping the construction light-weight.

Your questions:
  • is this a BD-illuminator? Yes. I only have an RMS turret though, so for the tme being I can't used the DF option. Also, the central shade broke off. I am afraid it wasn't damaged when I bought it. Looks repairable
  • lamp in the lamphouse? I have seen somewhere that the original Nikon lamphouse has a collector lens. I don't have one myself to confirm this. I do have an optiphot coming and I wonder if its lamphouse might fit the illuminator. Only now the American postal services are competing with the Chinese which can be the slowest...


Chris, do you think it would be a good idea to continue this discussion on photomacrography? I had thought since it is a truely microscopic topic it would be in place here, but it turns out a dialogue between the two of us.


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PostPosted: Fri Jan 25, 2019 5:29 am 
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Mike, the Nikon microscope guy, over at that forum, may offer you some answers on the Nikon epi illumator. I cannot remember his last name (Michell or Mitel?) or email, though he may have a Nikon epi scope.


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PostPosted: Fri Jan 25, 2019 5:29 pm 
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Does this require special objectives? Or will it work with, say, Phase Contrast objectives?
Also, can you use halogen illumination?
I ask because I have a couple of these illuminators but hey have Mercury vapor illumination.
I have the power supply as well, but don’t know enough about them not to cause an explosion.
Easy to adapt a halogen source if it is bright enough.
Radazz

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PostPosted: Fri Jan 25, 2019 5:37 pm 
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There are certainly some folk over there who would know more than me. I'm only an admin, whaddoIknow :) ?
I have two epi illuminators which seem compatible (not tried, Optiphot is in storage) one is the BD type (plastic thing) and the other has pol etc filters, is metal, and has a lamphouse.


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PostPosted: Fri Jan 25, 2019 6:11 pm 
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Radazz wrote:
Does this require special objectives? Or will it work with, say, Phase Contrast objectives?
Also, can you use halogen illumination?
I ask because I have a couple of these illuminators but hey have Mercury vapor illumination.
I have the power supply as well, but don’t know enough about them not to cause an explosion.
Easy to adapt a halogen source if it is bright enough.
Radazz
Mercury vapor illuminators are most probably fluorescence excitation sources. The only reason for "explosion" is rough handling. The real potential hazard is UV emission. So, if you turn on the lamp, verify ahead that the beam shines at a more remote surface, e.g. room wall. If it is lit when installed on the microscope, watch out for slots or crevices from which light might inadvertently leak. Long pass filters are needed to prevent unwanted UV, and ND filters are essential for dimming. They can be used for non-fluorescence epi illumination, and are extremely bright, but are not convenient.

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PostPosted: Fri Jan 25, 2019 8:13 pm 
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Quote:
Does this require special objectives? Or will it work with, say, Phase Contrast objectives?

Epi-illumination in itself does not require special objectives. Only, often it is used with thick specimens that cannot be viewed in trans-illumination, such as mineral samples. More often than not it is pointless or downright impossible to balance a cover glass on such specimens. And having no cover glass matters, so you'd be looking for no cover-glass objectives. Also, the Nikon epi-illuminators are not corrected for the additional tube length. So, when using epi, I change form 160/0.17 objectives to 210/-

Microscopic techniques that require cooperation between substage and superstage optics, such as phase contrast, are not possible (although who knows what you may achieve if you don't follow the manual).

Halogen lamps are not only a possibility in epi-illumination, in fact the original epis came with halogen lamps.

Wim


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PostPosted: Sat Jan 26, 2019 12:23 am 
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Yes they're completely different illuminators. Mercury burners (arc) is only used for fluorescence, really. I have 2 of those too, waiting. A fellow on that other forum explained that you can use tungsten or LEDs in place of a mercury burner, (or flash if you remove the UV filter, ) but the latter is a heck of a lot brighter down at the UV end.

Unless you have the right turret and BD objectives, the only other "technique" specific to epi-lighting is polarised light. Incident DIC and phase have been tried, but they aren't much general use. (Shiny metal flat surfaces.)


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