Olympus BH2 BHT/BHTU LED Lighting

[micro_pix]

This is a basic comparison between the standard 6v 20w halogen bulb fitted to the Olympus BH2 BHT/BHTU and the Retrodiode 10w LED OP10 replacement. All of the images were taken with the lamps on full brightness to avoid any issues with LED PWM dimming which I covered in the BH2 BHS LED topic viewtopic.php?f=25&t=43188. I found that both the standard halogen and the LED provided even lighting and Kohler illumination, the halogen was not as bright as the LED and has a very yellow cast. I chose a tough subject, some very small hyaline fungal spores (3.5 microns long), they are hardly visible in brightfield which meant that I could use the more light-hungry phase contrast to test the lights.
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For the top two images (of a defect in the coverslip glass) the camera was set to 5700k white balance, 1/100sec exposure and ASA 100. The microscope was in brightfield, there were no filters in the light path and both lights were at full brightness so the images show the colour cast and relative brightness of the lights. The bottom two images are central crops of images of the spores. These were taken using the 40x objective in phase contrast with the camera set on 1/8 sec and 100 ASA.
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These two images are the same images as the two above and have been edited to correct the colour cast, reduce noise, sharpen edges and match brightness - just to show the similar results after processing.

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The last two images are in phase contrast using a 100x oil objective. They show a clamp connection on a fungal hyphae. The images were made from stacks and have been edited to correct the colour cast, reduce noise, sharpen edges and increase brightness and contrast. The point is that both the Olympus 6v 20w halogen and the Retrodiode 10w LED will give good images even using a 100x oil objective in phase contrast, the advantage of the LED is that you will get a higher shutter speed - 1/6th sec here with ASA 100 compared to the 1.6 sec for the halogen bulb.

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Dave

[Pau]

Dave,

Thanks for the new comparison.
It's very surprising how well the maximum light intensity matches between two very different sources.

I principle a 10W LED will emit much more light than a 20W halogen because LEDs are more than 2X efficient than halogen. I guess that being the LED big an important fraction of its emission does not enter into the illumination train designed for a much smaller lamp filament.

Do your Olympus BH2 microscopes have permanent diffusers in the illumination path?

[micro_pix]

Hi Pau,

I would expect it to be a fair bit brighter than the 20w halogen too. I agree that the relatively large area of the light source means more lost light and the other factor here is that I was driving the LED at it’s max rated current from a bench supply, it is one of the earlier models from Retrodiode and I no longer have the original dimmer/driver. I did have the newer high frequency dimmer but was sold along with another 10w LED unit I had, I was hoping to get a replacement dimmer before the test but that didn’t work out.

From my own experience with the Retrodiode 10w unit on an Olympus BHT a CK2 and as a replacement for the lamp box on the BH2 MA Epi-illuminator, I would recommend it for photography over the OEM halogen, as long as it is used on full brightness to avoid any banding at higher shutter speeds. Full brightness is fine at higher magnifications or when using phase/D.I.C. etc. but ND filters may be required for low magnification brightfield

I don’t think there are diffusers in the BHT light path, I haven’t added any but I’ve also never really looked at the internal components in the base.

Dave