Flange Focal Distance

I am not a professor of optics.

That being said I do understand that there’s a lot to learn about hooking a camera up to a microscope and I am woefully ignorant of the minutia.

But this is science and it is full of venturing into the unknown, even if many have already figured it out.

So one of the problems I have been having with the Versamet microscope is that everything on the camera was out of focus compared to the eyepiece. I did a little correction with the fine adjustment focus knob to get around the issue. But being limited to a Canon 5D without live view meant I had to focus everything through the eyepiece. Cumbersome and uncomfortable are appropriate words here. This meant that the photo quality suffered.

Then I discovered Flange Focal Distance. It was something I was vaguely aware of but didn’t know it was critical. When light exits the rear of a lens heading for the image sensor (or film), the light rays aren’t actually parallel. Thus placing the sensor closer to or further away from the lens flange than designed can lead to a fuzzy shot.

From Wikipedia

From Wikipedia

Now it seems that the Leica M mount that originally came with the microscope had a focal distance of 27.8 mm while the Canon EF mount tops in at 44.0 mm. There’s enough of a disparity there to make me think that this may be a factor in my images.

Solving this issue should bring my eyepiece focus and camera focus to the same point. Hopefully it will also help my falloff problem and light up the edges of my pictures. Unfortunately with my microscope out on loan I can’t do anything about this at the moment. I’ll provide an update when I get a chance to tackle this problem.

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Silicon under the Versamet

So I wanted to offer an update on the Versamet 2 and the lens adapter. It works!
I even managed to take some shots with it before I loaned it out to a friend of mine with a Canon 7D who really wanted to do some digital microscopy.
I was having some issues with the communications contacts for the EF lens mount on the camera. Modern DSLR cameras actually communicate with electronics in the lenses in order to operate some of their features like Image Stabilization, aperture and focus. My metal adapter ring actually shorted some of the contacts making the camera error out. A little bit of sticky tape solved the problem.
The images were also suffering pretty badly from a falloff in light as you left the center of the image. I didn’t have enough time to track down the problem and the best solution I had was to crop out 3/4 of each shot.

But one of the neat shots that I took in a failed photomosaic was this. This is one of the pieces of silicon from a module that was given to me by a gentleman I met and struck up an engineering conversation with. It’s a failed copy of one of the chips that went onto the Cassini spacecraft that is currently orbiting Saturn.

Wire bonds and some alignment marks
I don’t understand enough about Silicon to give a truly accurate description. But this chip specifically has large feature sizes for even a 1994 vintage. It’s a feature called VLI. As I was informed by one of the gentlemen who helped design this chip, the feature size prevents high energy particles from switching transistor gates and possibly creating a latch up failure.

Think of a bowling ball launched at the door of your house. The ball will likely blow your door right in or cause enough damage that it’s essentially open now. Now imagine that same ball crashing into a 50 foot tall blast door. It may do some damage, but you can’t arguably claim that the door is now open.
It might be a brute force tactic, but it works pretty well.

Coffee and Science

At work we have a FLIR E60 thermal imaging camera. It’s an amazing little device and I want very much to take it home some days (I’d bring it back, I just want to see things). One day while we were setting up I happened to point it at the cup of coffee on my desk. What I saw was something I didn’t expect, but I should have.
Thermal Coffee

I had always assumed that my coffee was pretty static and once you had set it down and left it for a few minutes all of the internal flows would settle down. Boy was I wrong. The hot coffee forms unstable upwellings in the cup and cools once it reaches the air at the surface, then it sinks back down. The effect is like watching the top of a lava lamp, and for the exact same reasons.
I had already printed out an adapter to mount the camera to a tripod and decided that I should take a movie of the process.


Nothing happens at the end. Don’t wast all your free time.

At about 2 minutes in I gave the coffee a stir. It’s pretty neat to watch the vortex slowly fade into the unstable upwellings again.