Identifying vibration from on-scope sources

Blurry images can be caused by more than optical problems. I recently had a customer with a rather complex system tell me she was having focus/blur issues on her scope. When I inspected the system I found everything to be fine on the optical side, however, when viewing my sample and a short (10ms) exposure, I was shocked to see the image rocking back and forth!

After some investigation, I discovered that one of the users had wedged a stack of lens paper under the camera body, in an effort to change the camera’s field of view in relation to the confocal image. This in turn caused the vibration dampening system in the camera body to become ineffective, causing vibration to transmit down the rest of the scope. By removing this wedge, I was able to eliminate the vibration.

This experience got me thinking – how many systems are out there that are using air tables, but over time various power supplies (with cooling fans) or other devices are placed on the table, causing vibration and ultimately reducing image quality?

Testing Vibration

The reason i was able to detect a shifting image instead of the blurry image reported by the customer is simple – exposure time. The customer was using normal exposures in the 200-300ms range. This was long enough for the shifting image to be averaged into a smeared one. My sample is extremely bright, so I had a short exposure of ~10ms, and this was enough to catch the vibration. For any system you can also test this:

1. Place a bright specimen under the scope. Fluorescence will have higher contrast, but even an H and E slide with fluoresce at UV/DAPI brightly.
2. Set your camera exposure time to a short value (below 15ms of possible). Make sure your camera is set to “non overlapped”. Also – set the a/d converter speed as fast as possible. If you have trouble with etting the frame rate high enough for your needs or if the signal is too low at these exposure values, you can bin the camera to get more signal per exposure.
3. Set the objective magnification to the highest possible value.
4. Run a live image (with everything on your microscope turned on – incubators, light sources, everything!)
5. Does the image shake at all? If so, selectively turn off each device on your system (except for the light source and camera) until you isolate the source of the vibration.

As a side note, I found a really neat vibration recording tool for use with iOS devices. It’s called “Vibration” – here’s a description of the app. I tried this app by placing it on a few things like my laptop, a household fan and my tower PC, it’s quite sensitive, and exports a host of data. Here are some examples of the output.

I plan on using this tool to find vibration sources on customer’s systems in the future, and will report how well it works!

-Austin