Olympus BHM

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Koma Darkfield 1

BH-2 with a UMA 

The BH-2 microscopes from Olympus came in myriad configurations. Additionally, this series of scopes was manufactured over a significant number of years and many different models and features were added along the way.

This particular scope is a BHM – which is a BH-2 with a UMA illuminator that is set up for metallurgical imaging. The UMA is fitted with a 50W halogen lamp housing, as well as darkfield and lightfield half-mirror modules. The light path directs the illumination through the objective onto the subject. 

With the addition of different accessories, this BHM can also do polarized, DIC and fluorescence imaging. Presently – while I am interested in exploring all of this scope’s capabilities – I’m focused on darkfield illumination as well as using a fiber optic illuminator to create as an extreme off-axis light source.

My BHM was fitted with a standard field trinocular head and I’ve added a 2.5x photo eyepiece (relay lens) and a mount to accept a Nikon DSLR. I’ve been using my D7000 for most of my practice work but I will probably switch over to my D810 once I have all the kinks worked out.

I modified the original stage with the addition of an internally mounted neodymium magnet, and silicone pads. The magnet is quite strong and it holds straight razors in place securely.

Presently – I have 3 NeoSplan objectives in 5x, 10x and 20x. I also have a semi-apo 5x Mplan FL but I am not sure if I can make it work. This scope has a 180mm tube and the nosepiece has 26mm Neo Threads. My goal is to add a Neo Splan ULWD 50x to the setup, or possibly even one of the newer UIS2 ULDW objectives.  

Scope Working 1.jpg

To supplement the lighting from the integral UMA illuminator, I’ve added a fiber-optic light source to the setup. Basically – this is a power supply box with a lamp mounted inside of it, and a flexible fiber optic light-guide is attached to the front of the supply. 

I’ve rigged up a small clamp on a small weighted stand so I can position the end of the light-guide to point directly onto the sample I’m intending to view and image. 

 The lamp in this unit is an obscure 12V 150W MR18 type ELV, with a color temperature that’s approximately 2800K. The CRI is, presumably, around 95 or so – but I’m going to meter this soon just to see exactly where it’s at. 

In this next photo, you can see the working end of the light-guide throwing a nice splay of light across some slurry that has dried up on an Escher ‘rubber’ stone. The nice part about this lighting option is that it provides a powerful yet controllable off-axis source. 

FO BHM 1.jpg

3/26/2015

One of the challenges with this project is getting light on the subject when the working distance between the objective lens and the sample is miniscule; with the 20x lens in place, the working distance is about 1.0 mm.

The UMA illuminator is invaluable here – it projects light through the objective onto the subject; I can switch from brightfield to darkfield to change the angle of incidence, but there’s no provision for extreme off-axis lighting.

This is where the fiber-optic light comes in; I can position the ‘head’ to throw light exactly where I want it, and from the direction of my choice.

Getting the color balance right is tricky though. I don’t like to play too much in postproduction; I shoot what I want, how I want it – in the camera.  So – to help get my system dialed in, and eliminate unknown factors that can impeded my efforts, I did a little color analysis with the new Sekonic C700R Spectromaster meter.

As you can see – the light is pretty impressive, CRI is 95, and color temp is a it over 2800K. This is very helpful; I tried using LEDs but even the best panel that is priced within reason is too large, not directional enough, and it will only get me a CRI in the high 80s. So – the fiber-optic source has proven itself to be the best choice for my wants/needs.

C700R FO 1.jpg
C700R FO 2.jpg

3/26/2015

 Below, you can see the current setup with my D7000 sitting on top of the custom imaging coupler from Richard Kinch. The oculars are Olympus WK 10x, and the objectives are 5x, 10x, and 20x Neo Splans. The sem-apo MPLAN FL 5x is awaiting an adapter ring to match the 26mm Neo Splan nosepiece thread.   

The box for the fiber-optic illuminator is out of the shot, under the desk, and the tan box with the green dial on the right is the TH3 power supply for the UMA illuminator.

BHM 1.jpg


© Keith V Johnson 2014 - 2018