Microstar IV LED Illuminator

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BrianBurnes
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Microstar IV LED Illuminator

#1 Post by BrianBurnes » Sun Jul 19, 2020 10:21 pm

The 20W tungsten bulb of my Microstar IV started to feel a bit underpowered for darkfield/phase constrast and photography, and I've been working on a high-power LED illuminator to replace it. I wanted to preserve as much of the original scope as possible, so I picked components that would fit into the existing wiring/housing. This is truly low cost stuff - total cost of the components is around $20 - so this should work with most budgets.

The basis of the illuminator is a neutral white Cree XHP 50 module. At its maximum power of 18W it outputs about as much light as a 100W halogen, so it should be plenty bright.

The power supply is a dimmable constant current driver. Any supply with enough current will work, but I picked one that fits neatly into the cavity occupied by the original power supply of the microscope, so it does not have to be external.

The power supply is just narrow enough to fit into the back of the microscope, but the case has to be modified so that the wires come out the top instead of the sides. I simply filed holes into the case for this, and crimped the wires into a Molex 42022 connector that mates with the microscope's original wiring harness. Here are the new and old power supplies, side-by-side:

Image


For cooling, I'm using a cylindrical heatsink. I wanted the heatsink to protrude out the back of the scope for improved cooling, and this heatsink is about the biggest you can go to still fit into the 47.6mm bulb opening in the microscope body. The heatsink is undersized (rated only at 10W) but I don't plan on running the LED at full power. The square PCB of the LED module is just a bit too wide to fit into the microscope's bulb opening, and the corners have to be filed down. The original LED module has friction fit connectors, but I removed them and soldered wires with a molex connector to it instead. Here are the new and old illuminator, side-by-side:

Image


I designed a 3D printed attachment that holds the heatsink. It's designed to match the screw holes of the original tungsten bulb holder, and holds the module at the correct depth so that the LED sits at the same position in the microscope as the original filament:

Image


The power supply is intended to be used with a dimmer, but an adjustable potentiometer will work too. After some experimentation, a 10K logarithmic potentiometer gives about the correct brightness range, and I found one with the correct shaft length to replace the original potentiometer in the microscope, so the light can be dimmed with the same knob as the tungsten bulb would. I added an additional 660 Ohm resistor in series so the brightness adjustment range "feels right", but that is optional. The potentiometer and series resistors are crimped into the original wiring with dupont connectors in case I want to adjust these components in the future:

Image


The original wiring was modified to connect to the bulb with a molex connector, in case I want to play with different LEDs in the future:

Image


The power supply is attached to the back plate with double sided tape and mates onto the original wiring:

Image


The LED is plenty bright and even at its lowest power, microscopy is only comfortable with the neutral density density filter in place. I'm quite happy with it - the higher power is very useful for darkfield/phase contrast and when imaging with a camera. The finished product:

Image

Image


The heatsink runs a bit warm, as only part of it is outside and can rely on convective cooling. This is fine for now at lower powers, but I may modify this in the future for better cooling if I need higher power continuously.

apochronaut
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Re: Microstar IV LED Illuminator

#2 Post by apochronaut » Sun Jul 19, 2020 10:46 pm

That is a nicely done replacement. Looks like it belongs there. I use a Diastar quite frequently, so a 100 watt halogen system on that basic microscope body is quite familiar but I could always see using an led in a Microstar or even a Diastar in future. My big concern so far has not been adequate intensity but adequate quality of the light.

Would there be any chance you would have any photographic files previously done with the 24 watt halogen system, that you could diplicate with your led retrofit and make a comparison image? A prepared slide perhaps?

Zuul
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Re: Microstar IV LED Illuminator

#3 Post by Zuul » Mon Jul 20, 2020 12:21 am

I recently completed nearly the same retrofit. Yours is a much more polished implementation, I must say! I used a Cree XHP-35 topping out at 12W, but the smaller die should be very close in size to the original filament. (More knowledgable people people than I suggest that is important to retain performance.) I chose to couple the heat as directly as possible to the chassis rather than a finned heat sink. It seems to work well.

I chose a 5000k color rated at 90+ CRI. Do you know what color bin yours is?


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Zuul
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Re: Microstar IV LED Illuminator

#4 Post by Zuul » Mon Jul 20, 2020 12:36 am

apochronaut wrote:
Sun Jul 19, 2020 10:46 pm
Would there be any chance you would have any photographic files previously done with the 24 watt halogen system, that you could diplicate with your led retrofit and make a comparison image? A prepared slide perhaps?
If I pick up another stand (as seams increasing likely) I should be able to do a comparison when I move my LED to it. The current set-up has far to many problems affecting the image to make it worthwhile, I’m afraid.

hans
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Re: Microstar IV LED Illuminator

#5 Post by hans » Mon Jul 20, 2020 12:58 am

Very nice, I recently ordered some ~10 W, 90 CRI and ~1 W, 95 CRI LEDs to experiment with in my Microstar IV. Going to be too embarrassed to post whatever mounting kludge I manage after these though...

Brian, I was following your Microstar IV Camera Setup thread, curious if you have anything new to report there?

MichaelG.
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Re: Microstar IV LED Illuminator

#6 Post by MichaelG. » Mon Jul 20, 2020 3:16 pm

BrianBurnes wrote:
Sun Jul 19, 2020 10:21 pm
The power supply is a dimmable constant current driver.
.
Very tidy conversion, Brian ... and obviously effective !

That power supply had me confused for a moment though, until I downloaded the datasheet

“dimmable constant current” reads like a contradiction in terms; but I now realise that they mean that the constant [sic] current value can be varied.
... a strange quirk of language.

MichaelG.
Too many 'projects'

hans
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Re: Microstar IV LED Illuminator

#7 Post by hans » Mon Jul 20, 2020 10:24 pm

MichaelG. wrote:
Mon Jul 20, 2020 3:16 pm
... “dimmable constant current” reads like a contradiction in terms ...
In this context "constant" is meant to be interpreted as "constant despite changes in output voltage" rather than as a statement about whether or not the setpoint can be varied.

MichaelG.
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Re: Microstar IV LED Illuminator

#8 Post by MichaelG. » Mon Jul 20, 2020 10:48 pm

Yes ... that is what I deduced by looking at the datasheet

MichaelG.

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Too many 'projects'

BrianBurnes
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Re: Microstar IV LED Illuminator

#9 Post by BrianBurnes » Wed Jul 22, 2020 5:31 am

Happy to see so many LED conversions! The CRI of my LED is rated only at 70+, and I will have to do more testing to see if color accuracy becomes an issue. A higher CRI LED should be easy to swap in.

hans, sadly I don't have any new updates to report since my last post. I'm waiting to regain access to a 3D printer to more firmly mount a projection eyepiece, but things are moving slowly with the current world situation. I'm using a direct projection setup for now.

apochronaut: I happen to have two Microstar IV stands (a phase contrast setup and a brightfield one), and I've taken some test shots today of LED vs tungsten.

The prepared slides I have are somewhat low quality, but I made an attempt regardless. I moved the objectives and head from one stand to the other, so the comparison shots are taken with the same objectives/condenser/camera setup. The only difference is that the condenser rack on the tungsten stand is of the copper horseshoe type, and I can't seem to fully center the condenser in it. The vignetting is not symmetric in either stand in part because I have not aligned my camera setup since last tinkering with it, and in part because the arm holding the Bertrand lens protrudes slightly into the camera's field of view, causing some asymmetry.

The photos below are taken with the same camera shutter speed, but with different white balance to make them roughly equal temperature (I did this rather quickly so they are not quite identical). I'm using the blue filter for the tungsten bulb, and no filter for the LED.


Unidentified insect with 10x Neoplan, LED on the left and tungsten on the right (click for full size):

ImageImage


Same insect with 40x Plan, LED on the left and tungsten on the right (click for full size):

ImageImage


Diatoms with 40x Plan, LED on the left and tungsten on the right (click for full size):

ImageImage

It's hard to judge actual colors with the different white balances, but when looking through the eyepieces I personally find the background color more pleasing with the LED. The tungsten with the blue filter is a bit more blue and harsh.
When it comes to actual subjects the two perform about the same as far as I can tell, but I don't have particularly trained eyes when it comes to microscopy. At the least, photography is a lot easier at higher magnifications with the light output of the LED.

apochronaut
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Re: Microstar IV LED Illuminator

#10 Post by apochronaut » Wed Jul 22, 2020 2:34 pm

Thanks for the images. I know they take time and energy. It helps give me a baseline, especially from such an excellently thought out and executed system.
I'm probably known around this forum for being anti-led but this really isn't true. I recognize that led or other efficient illumination is important for our future from an energy consumption point of view but having an excellent illumination system for a microscope trumps an environmental consciousness for me. The small savings in electricity don't amount to much in the broader scheme of things. Personally, my net environmental footprint is negative, having saved and fostered the growth of a roughly 40 acre old growth forest over the past 40 years and managed to increase it by a further 30 acres, while continueing to produce pesticide free food for people, amongst many other aspects of an environmentally focused
life. Just to put the environmental case for leds to bed and so I can be forgiven for not jumping on the bandwagon.
I do use led illumination somewhat, mostly mixed into incident illumination. Typically for transmitted light situations, I have found it defective in that it reduces the potential contrast of most systems I have used it in and the colour balance is a bit skewed to excessive blue. This doesn't really matter that much if the ultimate goal is to obtain a photograph because all kinds of chicanery can be trotted out for that application but 99% of my microscopy is visual, and I would argue that to be true for most microscopists, so I need the optical parameters to be spot on. It's more of an if it ain't broke why fix it attitude.
To be honest, I don't use a Microstar much and when I do, I use a custom blue filter placed over the illuminator window. I find that colour balance , quite perfect. Mostly I use a Diastar, which has a group of filters in carousels fore of the already tinted collimating lens, so one can gang as many as 3, which gives the option of obtaining a perfect colour balance and contrast. Those factors become more important at high magnification, where the contrast and illumination can get challenged and everything the illumination system has going for it are sometimes needed.

I went over the images in some detail and have these comments. I'm considering your comments about the set up but am also just laying the cards on the table regarding my perceptions of the two illumination systems.


So, in your photos and in the system as a whole, I am looking for differences in 10 areas. 1) background homogeneity 2) background tint 3) resolution 4)contrast 5)subject colour 6)depth of focus 7) diffraction/ca 8) energy consumption 9) stage heat 10) durability. I would also include brightness but that is more a question of which of each is being compared, so it really isn't relevant.
I am not getting the pictures arranged left to right, so in the following comments I am considering the upper in my case, the ones with the greenish cast to be left or the led version.

1) I give a nod to the upper image,( led). I know that I can get a perfectly even background on the Diastar but in this case the led looks a little more even.,
2) I don't really like either. The led looks green and the halogen looks beige, although uneven at that. I'm pretty sure the halogen filtering can be improved but not sure about the led. I make it an even not great for either.
3) The halogen is clearly the better of the two with many fine details visible or sharper than in the led illuminated images.
4) Again the second image in each set is superior. It isn't so evident in the third set but it is still there. The led images lean in the direction of what I have found with fluorescent illumination: a bit of a flat washed out appearance.
5) Hard to tell. #3 is clearly heavily affected by the background. The other two look quite similar but the halogen image does have better contrast which gives it the appearance of having truer colour. less green?
6) Not too much to choose. They seem similar where the two images are focused equally.
7) This one is tricky because the lenses are achromats, so there is a small amount of native ca. Still , there are differences. Expanding the second set of images reveals a bit of a haze around the perimeter of the first in the pair and looking at the protruding round structure center stage, there is a small amount of yellow chroma clinging to it's edge that isn't there in the second image It is possible that is an artifact of a slight difference in focus.
The third set of images reveals that with with the led there is a shift towards a yellow and lavender chroma and with the halogen similar areas are red to magenta. The red does stand out a little more in that image but the yellow does in the other images.
8, 9 and 10 fairly obvious advantages for the led. For sure the energy consumption of an led is less and they are more durable. Stage heat wouldn't be a factor with a remote halogen but where the original bulb was under the stage or in close proximity , there could be a big advantage in that regard for the led.

Hobbyst46
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Re: Microstar IV LED Illuminator

#11 Post by Hobbyst46 » Wed Jul 22, 2020 4:26 pm

apochronaut wrote:
Wed Jul 22, 2020 2:34 pm
So, in your photos and in the system as a whole, I am looking for differences in 10 areas. 1) background homogeneity 2) background tint 3) resolution 4)contrast 5)subject colour 6)depth of focus 7) diffraction/ca 8) energy consumption 9) stage heat 10) durability. I would also include brightness but that is more a question of which of each is being compared, so it really isn't relevant.
I am not getting the pictures arranged left to right, so in the following comments I am considering the upper in my case, the ones with the greenish cast to be left or the led version.
My taste is also favoring halogen, and I think that the role of energy saving in microscopy is way over-emphasized by microscope makers and sellers. Especially if one considers the energy requirements of research facility microscopes, that use powerful lasers etc...
3) The halogen is clearly the better of the two with many fine details visible or sharper than in the led illuminated images.
Please explain point (3). I enlarged and cropped the 3rd row images and place them side by side (hope that the OP would not mind !). The LED is on the left. IMHO, the LED images are sharper, just some.
Attachments
LED-HALOGEN comparison.jpg
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BramHuntingNematodes
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Re: Microstar IV LED Illuminator

#12 Post by BramHuntingNematodes » Wed Jul 22, 2020 5:03 pm

I mean you can look at the spectral distribution of many LEDs and they are highly variable. The XHP50 described in the initial post looks to have a very similar distribution to the halogen with the exceptions of a quicker fall off near the red-infrared and an additional violet spike. A slight tradeoff of long wavelength light for more short might be useful for resolution of finer details.Some LEDs have exceptionally bad distributions, with spikes around three particular wavelengths and less light everywhere else. The main selling point I think for the halogen bulb is that their distribution follows pretty much the same pattern, so you don't have to do any research about the particular halogen lamp you are acquiring to know what qualities you are getting. Also they will be the same as old electric light for comparative research. In my experience though this means they all have a reddish cast without filtering.

The energy-saving argument is laughable for the amateur microscopist. Clearly marketing drivel to sell a few dollars of electronics as a big money upgrade.
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

MicroBob
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Re: Microstar IV LED Illuminator

#13 Post by MicroBob » Wed Jul 22, 2020 5:14 pm

Hi Brian,
that really is an interesting comparison!
The upper set is focussed a bit different which makes comparison difficult, The second set looks very similar to me, apart from exposure, white balance and colour intensity. Since all usual white LEDs have a dent in the spectrum at around 500nm, the opposite colour orange will be subdued. I think this shows in your bug photos too.
Depending on the subject this dent can really be a problem, e.g. in histological slides which are stained just in that colour range. So for a pathologist halogen would be preferrable over a usual white LED.

When I take photos of diatoms I usually separate the image in the RGB channels and use just one, typically the green channel. This removes the colour fringes and gives a better image than just converting to b/w. I assembled a comparison image which was edited with GIMP. I just used auto levels to get similar looking images, then took the green channel and cut out a little area that fits forum size limitations. Top is LED, bottom is halogen. I think the focus points are not absolutely exactly the same, but close. The ISO settings of the images are not the same: The LED image was made with ISO 400, the halogen image with ISO 1000. This shows in more noise in the halogen image. Taking into account the slightly different focus point and the different ISO settings the images are very similar to me.

So this is just what I would have expected: The LED is a bit weak at orange hues and both do equally well with colourless objects.

Bob
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Assembly green auto channel LED top halogen under.jpg
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Zuul
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Re: Microstar IV LED Illuminator

#14 Post by Zuul » Wed Jul 22, 2020 5:39 pm

I want to discuss one other potential benefit of LED because it's the one most appealing to me. It lies somewhere between conserved energy and sample heating.

Remote lamp houses are required for 100W systems to manage excess heat. If the same intensity of light can be obtained with LEDs using 1/5 or 1/10 the energy, it produces 80-90% less heat. This obviates the need for a remote lamp house, thermally speaking, and also allows for a more compact power supply. The overall system size is, therefor, significantly reduced.

Is there an optical performance penalty for not employing the remote lamp house?
(In the case of Microstar vs Diastar, you also loose the space for the multi-gang filter pack. I think it's reasonable to assume a similar feature could be engineered into the 410's available space if that were a goal during initial development, though.)

As a disclaimer; I'm a mechanical engineer working in product design along side industrial designers. My sensitivity to product size and ergonomics is hypersensitive compared to most folks.

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Re: Microstar IV LED Illuminator

#15 Post by BramHuntingNematodes » Wed Jul 22, 2020 5:47 pm

Zuul wrote:
Wed Jul 22, 2020 5:39 pm
Is there an optical performance penalty for not employing the remote lamp house?
If you can position your lamphouse several parsecs out you could be assured of well-collimated light.
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MicroBob
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Re: Microstar IV LED Illuminator

#16 Post by MicroBob » Wed Jul 22, 2020 5:57 pm

Zuul wrote:
Wed Jul 22, 2020 5:39 pm
is there an optical performance penalty for not employing the remote lamp house?
As a disclaimer; I'm a mechanical engineer working in product design along side industrial designers. My sensitivity to product size and ergonomics is hypersensitive compared to most folks.[/size]
1. That depends on the actual setup, but usually both lamps give equal light quality, just different intensities.
2. As long as the design adds to the function, it is well worth to design a product with more than usual care. We are surrounded by half-designed stuff that is just a nuissance.

It is a plus for a microscope to have moderate size and especially no protruding elements at the back. This makes it much easier to quickly move it when the space is needed. My Phomi 1 has not moved more than 10cm since I got it about a year back! And it has just a tiny LED heat sink protruding at the back, no big external lamp!

Bob

Hobbyst46
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Re: Microstar IV LED Illuminator

#17 Post by Hobbyst46 » Wed Jul 22, 2020 6:19 pm

Zuul wrote:
Wed Jul 22, 2020 5:39 pm
Is there an optical performance penalty for not employing the remote lamp house?
There might be. In a microscope that has collimating lenses in the base, the lamp should be positioned accordingly to provide Kohler illumination. Removal of the external lamp housing that changes the distance between the lamp and the next optical train element must take this into consideration.
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apochronaut
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Re: Microstar IV LED Illuminator

#18 Post by apochronaut » Wed Jul 22, 2020 6:21 pm

Hobbyst46 wrote:
Wed Jul 22, 2020 4:26 pm
apochronaut wrote:
Wed Jul 22, 2020 2:34 pm
So, in your photos and in the system as a whole, I am looking for differences in 10 areas. 1) background homogeneity 2) background tint 3) resolution 4)contrast 5)subject colour 6)depth of focus 7) diffraction/ca 8) energy consumption 9) stage heat 10) durability. I would also include brightness but that is more a question of which of each is being compared, so it really isn't relevant.
I am not getting the pictures arranged left to right, so in the following comments I am considering the upper in my case, the ones with the greenish cast to be left or the led version.
My taste is also favoring halogen, and I think that the role of energy saving in microscopy is way over-emphasized by microscope makers and sellers. Especially if one considers the energy requirements of research facility microscopes, that use powerful lasers etc...
3) The halogen is clearly the better of the two with many fine details visible or sharper than in the led illuminated images.
Please explain point (3). I enlarged and cropped the 3rd row images and place them side by side (hope that the OP would not mind !). The LED is on the left. IMHO, the LED images are sharper, just some.
I didn't refer to that image because I found it difficult to read. The terrible level of weird lavender/blue/yellow ca kind of distorts the led image. Looking at your comparison, I can see several key areas where the led appears to render a more highly resolved image but there are also areas but not so obvious ones, where the halogen seems sharper. I think it is a case of not exactly the same focus point.

My reference images for that opinion were the second pair. The enlarged sections of pair 1. Both the resolution and contrast particularly show more favourably towards the halogen lighting.

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Re: Microstar IV LED Illuminator

#19 Post by BramHuntingNematodes » Wed Jul 22, 2020 6:37 pm

Oh yeah another thing to think about when doing digital photography under the scope is that LED bulb attached to household AC or from certain power supplies or even this one battery powered flashlight I had can induce some horrendous flickering and banding, particularly when attached to a cheap dimmer. This problem was eliminated for me in one case by using a more expensive LED dimmer and in another by using a relatively high quality DC power supply.
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

apochronaut
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Re: Microstar IV LED Illuminator

#20 Post by apochronaut » Wed Jul 22, 2020 6:58 pm

Zuul wrote:
Wed Jul 22, 2020 5:39 pm
(In the case of Microstar vs Diastar, you also loose the space for the multi-gang filter pack. I think it's reasonable to assume a similar feature could be engineered into the 410's available space if that were a goal during initial development, though.)
The AO 20, which lived a 1/2 life as a transmitted fluorescence microscope has a 2 gang filter carousel arrangement between the mirror and the illuminator exit port instead of in front of the lamphouse.

Part of the complement of filters were fluor. filters but they just rested in their seats because the carousels were horizontal. The places can be used for any filters of the correct size. This didn't make the 20 smaller. In order to reduce the size of a 100 watt microscope somewhat and include the filters , a horizontal slider might need to be employed but this would increase the lateral footprint of the microscope.
One thing being overlooked here is the benefit of a large heavy microscope for stability with high resolution . I use high resolution , high magnification a lot and larger, heavier , microscopes make the job of obtaining stable images and photographs at 1400X and 1.4 N.A. a little easier.

Zuul
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Re: Microstar IV LED Illuminator

#21 Post by Zuul » Wed Jul 22, 2020 7:25 pm

Hobbyst46 wrote:
Wed Jul 22, 2020 6:19 pm
Zuul wrote:
Wed Jul 22, 2020 5:39 pm
Is there an optical performance penalty for not employing the remote lamp house?
There might be. In a microscope that has collimating lenses in the base, the lamp should be positioned accordingly to provide Kohler illumination. Removal of the external lamp housing that changes the distance between the lamp and the next optical train element must take this into consideration.
Agreed, but I’m not talking about changing an existing optical path. I’m suggesting that a microscope correctly designed for in-base illumination could have the same brightness as the external lamp house. In that case, would there be a downside?

Hobbyst46
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Re: Microstar IV LED Illuminator

#22 Post by Hobbyst46 » Wed Jul 22, 2020 7:51 pm

Zuul wrote:
Wed Jul 22, 2020 7:25 pm
Hobbyst46 wrote:
Wed Jul 22, 2020 6:19 pm
Zuul wrote:
Wed Jul 22, 2020 5:39 pm
Is there an optical performance penalty for not employing the remote lamp house?
There might be. In a microscope that has collimating lenses in the base, the lamp should be positioned accordingly to provide Kohler illumination. Removal of the external lamp housing that changes the distance between the lamp and the next optical train element must take this into consideration.
Agreed, but I’m not talking about changing an existing optical path. I’m suggesting that a microscope correctly designed for in-base illumination could have the same brightness as the external lamp house. In that case, would there be a downside?
The spectrum of the white LED has a dip in the green and a strong spike in the violet-blue, whereas the halogen yields more "natural" light. However, some folks have already found novel LEDs dies that have an CRI of 90+, or 95+. Such LEDs may improve microscope illumination considerably.
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

hans
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Re: Microstar IV LED Illuminator

#23 Post by hans » Wed Jul 22, 2020 8:19 pm

Hobbyst46 wrote:
Wed Jul 22, 2020 7:51 pm
... LEDs dies that have an CRI of 90+, or 95+ ...
The 95+ CRI ones I ordered to try are these:
https://www.digikey.com/product-detail/ ... -1392-1-ND

They are the highest luminance I found with such a smooth spectrum:
sunlike-spectrum.png
sunlike-spectrum.png (65.26 KiB) Viewed 2748 times
(WW, NW, CW refer to warm, neutral, cool white.)

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