So apparently my theory on Flange Focal Distance being a factor in my focusing problems seemed to be a dud. It turns out that I can hold the camera actually a fair distance away from the flange mount without any observable degradation in image quality.
In hindsight this makes some kind of sense. As the microscope acts as the camera’s lens, the light hitting the sensor must be relatively parallel.
To test this I actually decoupled the camera from it’s mount and shot lens-less from a ways back in a darkened room.
So going from fully attached to several dozen millimeters out changed my image impressively little.
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.
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.
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.
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.
One of the reasons that I bought my Canon 5D was to be able to share some of the interesting things I’ve seen through my Versamet 2 Surface Microscope.
The problem is that Unitron only made adapters for Lecia cameras. My EOS camera takes the EF series of lenses. Unfortunately I can’t seem to find any engineering drawings of the lens mount online.
My solution is to make my own from scratch. A little turning here, a little CNC code there and I should have it.
Here is the Solidworks rendering of the lens adapter. There are a few things I found difficult to measure, but I should be able to make do.
When I’m done with this, I’ll have the engineering drawings available so the next guy (or girl) will be able to skip this step.
Hooray for Machine Shops.
The Versamet 2 is an old Metallurgical microscope used for looking at the grain structure of highly polished sample pieces in a lab. It does this by using a type of lens that directs light at your sample and looks at the reflected image at impressively high powers for a visible light microscope.
One of the neat features is that it’s designed to take photographs of your part. The majority of the bottom half is set up to reflect the image onto a Polaroid film cartridge with an option to send the image to an attached 35mm camera. It even comes with an exposure control unit to accurately run the internal shutter.
The beauty of a reflected light microscope is that you can look at opaque objects. Vintage razor blades are a personal favorite of mine. The microscopic world is amazing in the things that you can see in a traditional microscope, but the things you can see with a reflected light microscope are that much again astounding.
Like many of my odd toys, I picked this one up at an industrial auction. Best $25 lot I’ve gotten so far.