How to Clean Microscopy CCD Camera Windows

Disclaimer: Cleaning the sensor window is a delicate task and you can potentially damage your sensor forever, which most likely will not be covered by the camera manufacturer warranty. Please contact your camera manufacturer to determine what method of cleaning is recommended by them!!!

This is a question I run into a lot in the field. A customer has a camera mounted on a microscope and somehow, over a long enough period of time, the CCD window is covered with dust. This dust shows up visibly in transmitted light images and can be a huge pain to remove.

First it's good to understand why a window must be in place: Microscopy cameras, and all CCD's for that matter, generate electron charges inside each pixel when the CCD is hot. What this does in a low light application is create an ever-increasing noise floor which will follow signal as exposure time from the camera is increased. This is an ever-increasing amount of noise expressed as Electrons generated Per Pixel Per second. (More on noise can be found here)

In order to reduce this noise microscopy cameras are cooled, most commonly using a thermoelectric Peltier device which sucks heat away from the CCD and dumps it into a heat sink on the other side. (This is why most cameras are rather big - they have a huge copper heat sink attached to the hot side of the peltier device).

Anyway when the CCD is cooled to anywhere near dewpoint any ambient moisture will condense on the CCD. Suffice it to say CCD arrays and moisture don't like one another. So we have to cool the chip but keep moisture away from it. The way this is done is by creating a dry environment in a sealed chamber, with the CCD on one side and glass on the other. This is the glass we have to clean in order to get our pretty picture.



Next are the options for cleaning the glass. A few points here:

- As a general rule if you've never cleaned the window it's best to aviod it as long as possible. Once you clean the glass you will create very small imperfections in it that are not visible, but that will collect dust more easily than when the camera was new. This is unavoidable but just keep in mind it's good to wait until you can't stand the image any longer!

- We want to use a method of cleaning that:
a. Is as non abrasive to the glass (as much as possible)
b. Leaves behind no residue or evaporates
c. Does not damage the seal used on the CCD window
d. Is simple for the neophyte to perform.

With this in mind let's look at our options:

1. Use Air
2. Use lens cleaning paper and ethanol
3. Use other products designed for optical cleaning.

1. Using air is a fast and simple method of cleaning the glass. A couple of notes on performing this correctly:
- Avoid using air contained in a hand held can.
The Propellants from the can can attached to the window and aren't easy to remove.
- If you have house air or nitrogen this is the best option.
- Try to blow dust off and away, not into, the glass.

2. Lens Cleaning Paper can be used in combination with a Spatula and ethanol. There is a good link to all of these methods Here.

3. One product I've seen used is a solution made for optical surface cleaning. I'll provide more info on this once I get an opportunity to try it.

So that's it. Be gentle, start with air first and go slow!