Quick cheap & easy LED conversion for my Halogen 'scope

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mrsonchus
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Re: Quick cheap & easy LED conversion for my Halogen 'scope

#61 Post by mrsonchus » Sun Jan 15, 2017 8:19 pm

[quote="Oxalis80"
................ Maybe I should remove / replace the opaque filter.[/quote]

Hi, yes, the almost-white LED will be blue due to the filter, which has been effectively filtering your 'reddish light' - just remove the blue filter as you won't need it with the LED.

Good luck.
John B

AndyMilman
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Re: Quick cheap & easy LED conversion for my Halogen 'scope

#62 Post by AndyMilman » Sat Jul 29, 2017 3:33 am

After reading this forum, I tried what I think you did: I bought a few different kinds of LED replacements for the halogen bulb in the vertical illuminator in one of my Meiji microscopes. I had been looking for a cheap way to increase the episcopic illumination. (I haven't tried it on the lower illuminator, where there's already enough light.)

It didn't work. I tried several brands of LED bulb and different positions of the bulb inside the lamp housing (about 60 mm on a side). The Meiji housing doesn't have a lens or mirror to focus the light into the microscope.

If you take a mirror, place it where a slide would be, and look at the bulb through the eyepieces, you can see that the light is coming from only one of the individual LED's in the bulb. Given the constrained space, I don't see how this could be overcome without re-designing the lamp housing. That's why I tried running it at a higher-than-nominal voltage (I discuss it in another forum). Overvoltage, it turns out, has its own pitfalls. :oops:

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coominya
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Re: Quick cheap & easy LED conversion for my Halogen 'scope

#63 Post by coominya » Sun Mar 25, 2018 8:56 pm

After reading this thread I decided to experiment myself as I have a lot of LED stuff laying around. What I quickly came up with was this.
A 1800LM T6 LED Bicycle Headlamp, off one of my bikes. It took all of one minute to setup, even with axial alignment. I think, among other things,
it needs an field diaphragm as even with the condenser diaphragm stopped right down it's intolerably bright with a 10x objective.
The photo is of a water leaf through a 40x obj @ 400x via the EP with a phone camera.

I might try and mount it in a spare lamp housing I have.

Image


Image


Image


Spare Housing.

Image

Hobbyst46
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Re: Quick cheap & easy LED conversion for my Halogen 'scope

#64 Post by Hobbyst46 » Sun Mar 25, 2018 9:14 pm

Neither the condenser aperture diaphragm nor a field aperture diaphragm are there to control the brightness of illumination. The field aperture broadens or narrows the beam. The condenser diaphragm modifies the contrast.
To change the brightness of the illumination source (your LED) itself, you need a dimmer. Note that a PWM dimmer can create dark bands in the photos, unless its frequency is very high. A controlled constant current source is better but maybe not so common. Alternatively, and perhaps less expensively, place neutral density filters on top of the LED.
Was the original halogen lamp of the microscope configured for Kohler illumination? because the LED replacement might eliminate that important feature.

MicroBob
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Re: Quick cheap & easy LED conversion for my Halogen 'scope

#65 Post by MicroBob » Sun Mar 25, 2018 9:31 pm

I would suggest to critical compare the image you get with the two illuminations. If the image with your bicycle lamp is bright but looks somewhat overly contrasty as if you have your condenser aperture closed too much the light beam might be wrong.

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mrsonchus
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Re: Quick cheap & easy LED conversion for my Halogen 'scope

#66 Post by mrsonchus » Sun Mar 25, 2018 10:28 pm

This is what I now use exclusively, having compared them with the Leitz ND filters for my Orthoplan and found no difference in image quality or properties whatsoever....
This filter simply rotates (two plates of what look like polarised glass) to alter the brightness. I place it over the light-port in the Orthoplan's base and hey-presto! No change in white balance etc in use - exactly the same as the fixed Leitz ND 'lollipop' filters but 'all-in-one' and variable between a '2' and a '400' ND range.

link to variable ND filter...


I've been using this on both my Orthoplan and SM-LUX - allowing the bulb to be left at it's optimum (near-maximum) level at all times - I use a blue filter also to take any warm tint out of the lamp's light. This simple device is superb, and cheap!

The link isn't the actual one I bought way back - but it's exactly the same thing - just pick a diameter to suit that will sit nicely over your light-port...

John B.

p.s. I made a comparison ages ago between the fixed lollipop ND and this variable ND - here's a rather low-res side-by-side comparison image I took at the time; I think the fixed is on the left, the variable on the right, not certain...
ws_ND filters fixed vs variable.jpg
ws_ND filters fixed vs variable.jpg (59.71 KiB) Viewed 8779 times
John B

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coominya
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Re: Quick cheap & easy LED conversion for my Halogen 'scope

#67 Post by coominya » Mon Mar 26, 2018 11:36 am

Hobbyst46 wrote:Neither the condenser aperture diaphragm nor a field aperture diaphragm are there to control the brightness of illumination. The field aperture broadens or narrows the beam. The condenser diaphragm modifies the contrast.


Yes you are quite right, I was just in a rush this morning, it was a spur of the moment thing and I wasn't thinking critically.

The LED light runs off a single lipo cell, nominally around 4V, and at the brightest setting incorporates no PWM. I'd run it off a small 6V SLA Battery I have and control the current/voltage with a rheostat, after dropping the voltage to 4V via a couple of big ceramic resistors.


Image

Image
Hobbyst46 wrote: Was the original halogen lamp of the microscope configured for Kohler illumination? because the LED replacement might eliminate that important feature.


tungsten lamp actually, but it looks like the led lamp will fit easily into the rear cell (after I gut it) and I can use the same alignment screws as for the other (theoretically)

Image

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coominya
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Re: Quick cheap & easy LED conversion for my Halogen 'scope

#68 Post by coominya » Mon Mar 26, 2018 11:39 am

MicroBob wrote:I would suggest to critical compare the image you get with the two illuminations. If the image with your bicycle lamp is bright but looks somewhat overly contrasty as if you have your condenser aperture closed too much the light beam might be wrong.
Yes, there is a bit of work to do on the project yet.

Hobbyst46
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Re: Quick cheap & easy LED conversion for my Halogen 'scope

#69 Post by Hobbyst46 » Mon Mar 26, 2018 11:55 am

tungsten lamp actually, but it looks like the led lamp will fit easily into the rear cell (after I gut it) and I can use the same alignment screws as for the other (theoretically)
Yes, I believe you can get everything to work just fine. 8-)

Hobbyst46
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Re: Quick cheap & easy LED conversion for my Halogen 'scope

#70 Post by Hobbyst46 » Mon Mar 26, 2018 1:22 pm

MrSonchus:

I have just re-read this 2yrs-old post from head to toe and enjoyed your methodical and efficient LED conversion for the compound microscope!
And I am considering a similar conversion to revive an orphan Zeiss Standard stand, that came without any illumination source.

Anyway, since the post is still active, I take the liberty to ask:
a) Does the PWM dimmer comply with photography? I mean, do you get horizontal bands in the background of the image, like stripes, with this dimmer? When I use PWM dimmers, especially the same one as yours, I have to limit the camera shutter duration to 1/250 sec (sometimes 1/500) or LONGER, to prevent the bands.
b) Are your 3W and 5W LED discs (or rectangles) attached to heat sinks?
c) Since I do not have any lamp besides LED, is there an easily prepared brightfield color image to which I can compare photos taken with LED? for example, onion epidermis stained with several common dyes (say, methylene blue, neutral red, toluidine blue, etc), so I can visually judge color rendition?

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75RR
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Re: Quick cheap & easy LED conversion for my Halogen 'scope

#71 Post by 75RR » Mon Mar 26, 2018 4:12 pm

Does the PWM dimmer comply with photography? I mean, do you get horizontal bands in the background of the image, like stripes, with this dimmer?
You might want to look into the BuckBlock DC LED Driver, as a constant current driver it avoid horizontal bands is stills and in video.

https://www.ledsupply.com/led-drivers/b ... led-driver

+ this article on a conversion of the Zeiss 12v 60w lamphouse

http://www.microscopy-uk.org.uk/mag/art ... ersion.pdf
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus E-P2 (Micro Four Thirds Camera)

Hobbyst46
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Re: Quick cheap & easy LED conversion for my Halogen 'scope

#72 Post by Hobbyst46 » Mon Mar 26, 2018 5:09 pm

Thanks 75RR. Both links are informative and worth reading. The second link is not directly relevant, since I have no external illumination unit. I think that these units were produced for the WL model and not to smaller or older Standard models - the original illuminator for the GFL is a mere lamp socket that fits inside the round base...

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75RR
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Re: Quick cheap & easy LED conversion for my Halogen 'scope

#73 Post by 75RR » Mon Mar 26, 2018 5:16 pm

I think all of the rectangular base standards can take the external 12v 60w lamp-house, don't think the round base ones can though.
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus E-P2 (Micro Four Thirds Camera)

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