VERSATILE AND PLEASANT LED LIGHT FOR ZEISS GFL

[Hobbyst46]

I thought I should share my experience in this forum.

I purchased my old used ZEISS GFL, which is a great little microscope, but decided to replace the original 6V, 15W tungsten-lamp power with a more modern and reliable illumination setup. Various home-made LED upgrades have been described. The electrical circuits and wiring involved are simple enough, but the mechanical and optical coupling of a LED to the microscope are more challenging - in particular when the microcope is fitted with collector lenses and field aperture.

So I solved the problem with a LED illumination setup from RetroDiode of Texas. It fits very well within the base of the GFL. Kohler illumination is OK. Moreover, the 6500K color temperature, 10W LED provides MUCH more light than the original tungsten bulb, without paying the price of emitted heat.
However, there were two issues that I had to deal with.
One was the periodic dark bands visible by the camera (hand-held iphone 5S on top of the eyepiece). The source of these was probably the standard simple 12V dimmer. A 21KHz dimmer from RetroDiode removed this problem.
The other issue was that the LED light is excessively blue to eyes that have been used to tungsten or halogen light. This is more a matter of personal preference. I believe that the blue-white 6500K light will be advantageous for some application. But for the piece of mind, I chose to add a warm-up filter. Transmission spectra indicate that a Hoya LA120 should do a good job, but I could not find it at a reasonable price. So I got an equivalent KR12 filter off Ebay, for a quarter of the price of the LA120. The KR12 filter can be placed on top of the field aperture.
It provides an acceptable hue of the brightfield, very much like that of a halogen bulb light.
The photo below shows the setup, with the filter in front.

[billbillt]

Hi,
I would like to see your photo, but it does not appear...

The Best,
Billt\T

[Hobbyst46]

Sorry - photo was too large...
now added 2 photos

[billbillt]

Thanks for sharing.. This is an interesting setup...

BillT

[KurtM]

Thank you for a very interesting post, had never heard of Retro Diode before. I have home-brewed LED illumination conversions in two microscopes, an AO One-Twenty, and AO Series 10, which is battery powered for cordless operation (my travel scope, have it with me right now in west Texas). They perform well, although I gotta say I'm pretty much spoiled on 100W lamps any more.

All of my conventional lamps, including separate vintage "research lamps", are equipped with blue filters to yield neutral white illumination with no descernible blue nor yellow tones. The LEDs were carefully selected for neutral white light, perform as advertised, so no filters needed for them. I find it interesting that your "temperature" preferences go in the opposite direction. I agree it's personal preference, as far as I know, just thought I'd toss in the comment.

Very nice scope! My primary stand is a classic Zeiss "black beauty" too.

[Hobbyst46]

Thanks, BillT and Kurt for the encouraging replies.

Kurt - seen your microscope collection presentation in the second link. Very impressive demonstration that fine microscopy is mostly based on the love and proper care of the instrument.

RetroDiode is on the site www.retrodiode.com.

I agree that neutral white may be a better choice. The my LED is a 6500K, visually it is not neutral. But your remark reminded me that when I get a dedicated camera, I will probably have to experiment with both optical filters and camera software to get the best white background!

[KurtM]

On the other hand, it's still personal preference. Photomicrography is an art, and as such, you're not obliged to make it look like anyone/everyone else's. Go with whatever pleases your eye most.

[billbillt]

Yes, LED color preference is a personal choice.. I just prefer the "warm white" (2800 - 3500K) look.. It just looks more like natural sunlight to me, instead of the fluorescent tube look of the "cool white" LED's


BillT

[75RR]

Agree that it is a personal choice ... one that both you and your camera have to agree on!

[Hobbyst46]

Thanks 75RR for the emphasis, I fully accept. Progressing step by step, now to improve the photo-micrography skills. Some diatom photos are due to be shown on the slide and specimen forum.