using a microscope and help with lighting

Khukuri Monster

Khukuri Monster

Joined
Aug 4, 2004
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373
I recently got an old doctor's microscope from my grandfather, with magnification levels of 100x, 440x, and 950x. The model is very similar to this one: http://www.arsmachina.com/spencer_new.htm except it is not nearly as shiny looking.

I was hoping that I would be able to use this microscope to take a look at the microstructure of steel. What sort of magnification levels are necessary for this?

Also, I've run into a problem with lighting. Normally you look at glass slides, so you can get enough light by using the mirror and condenser from below. However, when you look at something opaque like a piece of steel, you would need to light it from above.

Because of this, I can't get enough light to get visibility at magnification greater than 100x. I got the best results by looking through the microscope at early morning when the sun was low enough to shine directly on the flat surface of the piece of steel.

100x is not nearly enough to see anything in terms of microstructure, but I can look at the edge of a knife just to see how finely polished it is.

Does anyone have advice for a lighting system so I can use the higher magnification setting?
 
Usually these days you would use a fibre optic illuminator with either stereo fibre optic wands that can be positioned to cause no shadowing or a fibre optic "ring light" that surrounds theentire objective lens area. These can be fairly expensive. Used they can run several hundred bucks. They generally use a halogen bulb with a variable brightness control.

When you get into magnifications near 1000x, the lens is often specified as "oil bath" which means that it needs to be immersed in an optically clear oil on top of the slide to reach full magnification. Really high rez like that is hard to achieve without expensive gear. Microscopes are designed for different tasks. A medical mic might not be the right instrument for the task at hand. I would think that to view steel grain structure, 1000x would be overkill. Looking at a ground or polished blade would show you surface finish, not the grain structure itself. I'd think you'd have to flex a blade to failure, then look at the broken part to see the grain structure itself. You might be able to etch the blade to reveal the structure without destroying the blade (non destructive testing).

John
 
Your basic problem is that the biological and metallurgical microscopes are different .With tissue you can shine light through the sample but metals are opaque.The metallurgical microscope has a mirror system .the light shines down from above and is reflected.There's no way to convert the lighting system of a biological microscope .Sorry !
 
If the sun works, then just get one of those cheap adjustable spotlights with a base and stick a 150 watt plant bulb in it. That ought to light it up like the sun does.
 
Raw light output isn't always the right answer. The reason that real mic illuminators are variable output is that depending on what you're looking at, too much light will wash out the image. You also want to be careful about looking into high magnification optics at something that might reflect a really bright light source. It can be really hard on your eyes.

John
 
The metallogrqaph I had experience with had through-the-lens lighting. It was powered by a carbon arc light. Modern metallographs look like they still use thru-lens but with more modern light sources.

We used oil immersion lenses and magnifications up to 1000x to look at the crystal structures of cemented tungsten carbides and alumina ceramics.
 
Using that microscope to look at metal is quite impossible. I'm already very surprised you could see anything at 100x.
For looking at opaque objects you need a different instrument that forms a 3D image. It reflects light under the right angle to form a nice image.

But, this stuff is quite complicated, it takes a few hours to explain the details of your microscope. I'm not even going to start on that :).
 
Zwaplat said:
For looking at opaque objects you need a different instrument that forms a 3D image. It reflects light under the right angle to form a nice image.
Click to expand...

Like the Bausch & Lomb StereoView7 sitting on my wife's bench just outside my shop :) It's not a Leica or a Zeiss, but is awesome for hobby work.

Then there's the American Optics thing in the corner with darkfield capability.

My wife has worked in Q/A, inspection and Metrology for years. We really don't need scopes of this quality for any serious work, but we both find them facinating and appreciate good optic gear. Someday I'll find the right deal and the B&L will go away and I'll get me one of them nice German or Swiss rigs :)

John
 
Thanks for the help. It's too bad that I can't use the microscope for looking at steel, but at least it is interesting for looking at other stuff. Plus it looks neat sitting in my room.
 
I've got one of these http://www.microscopesusa.com/Vision.html (10x30 with supplemental lenses and extra eyepieces so I can get between 5x and 120x) and love it.

While you probably won't have any luck at the higher powers, you should be able to look at edges and things with the low power if you can direct some light down onto the surface with something from the link I posted above. Or, even something like this flashlight fiber http://safetycentral.com/safetycentral/fibopnitizem.html and tape the fiber to the low power objective so it points down at whatever you're looking at. It is only 6 bucks so you're not out much if it doesn't work out all that well, but you'll never know unless you try!
 
Yes, I think I am hooked. I was looking at eBay and, well...

Does anybody have advice or links to online advice for buying a metallurgical microscope? What sort of price range would I be looking at? I see some cheaper metallurgical microscopes on ePray for around ~$500 but I could be looking at complete crap and not know it. I tried doing a few internet searches but haven't found any good advice yet.

It would also be nice if anyone knows of a webpage which explains how these things work.
 
No specific experience with metallurgical scopes themselves, but I would note that the most useful all around scope is a stero microscope on a boom stand. The boom stand adds some cost, but adds a lot of flexability over a standard desktop stand.

John
 
"Monster", I notice that your URL is at U. Michigan. If you are at the university, you may have an excellent resource at hand. I am not certain, but would think they may have a Materials Science department at a school that size. I would hop over there some day and chat it up a bit. If so, they'll have metallographs. Also, if you Google the word "metallography", there are a bunch of useful sites come up.
 
That's a pretty purpose specific scope. I'd put the cash towards something stereo with more versatility.

John
 
John, while I don't have anything at all against a stereo boom, in this case I don't know if it would be right for looking at crystal structures microscopically. I'm don't know it's powerful enough to see grain boundries and such.

I am not certain, however, since my 1 year's experience 35 years ago was with tungsten carbides and aluminum ceramics. I do know that in that case we had to go to 1000x and use oil immersion on an etched sample to see what we needed on a through-the lens lighted metallurgical scope. I do not know how the grain sizes compare with steel.

That is why I suggested he contact someone with experience. A friend had some micrographic work done on some 52100 at the U. Mississippi and the grain was smaller than their charts could accurately define and they had a hard time seeing it.

I have nothing against steroscopes, mind you. :) I just got one two weeks ago to use with engraving and it is simply wonderful how much I can see detail again. While I am having to get used to the limited field of vision, at least I can see the lines again. To look at edges or breaks in test blades, I'd have to concur it'd be excellent at even 40x.
 
I guess my suggestion was for something more generally useful, although not so good for the specified purpose. It might make a difference to know if he's looking for a particular application in an industrial sense, or is just looking to see little things close up in a curiosity kind of way.

On a side note, while I've been trying to get my wife interested in my knifemaking hobby for some time, it's only after this past Solvang show that she seems inclined to put her scope skills to work to try a little scrimshaw (yeah!).

John
 
jmxcpter said:
On a side note, while I've been trying to get my wife interested in my knifemaking hobby for some time, it's only after this past Solvang show that she seems inclined to put her scope skills to work to try a little scrimshaw (yeah!).
Click to expand...

Check out this scrim:

http://www.thecarvingpath.com/forum/index.php?showtopic=134

On the microscope, I totally agree that scope of purpose of the unit (pun intended!) needs to be defined first. :)
 
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