Going Digital: Shutters and More

Choosing a microscope camera means making a decision that often gets overlooked: what kind of sensor is inside it.  But what are the choices and what do they even mean? It’s time to demystify some of the more common and confusing verbiage.

Digital Camera Terminology

These are a few terms you will commonly find when reading about digital cameras that often go unexplained:

CCD, CMOS, and sCMOS:

CCD stands for Charge-Coupled Device.  CMOS stands for Complementary Metal Oxide Semiconductor.  They refer to different ways that digital camera sensors can be manufactured.  Generally, CCDs are an older technology.  CMOS sensors are newer, and are designed to be much cheaper to make.  The term sCMOS is occasionally used, which stands for Scientific CMOS.  There is no formal definition for what makes a camera scientific, but these are almost always high-end sensors designed for quantified imaging, and are often cooled. 

Global Shutter and Rolling Shutter

A global shutter functions exactly how you would expect a classical camera to work.  The whole image is exposed at once.  Then exposure stops.  Finally, the image data is transferred.  All CCD digital cameras (and all classical film cameras) work this way.  The process of sequentially starting, stopping, and transferring data is a major speed limiter for these sensors.

A rolling shutter starts exposing at the top line of pixels, then activates the rest of the pixels one line at a time.  Stopping the exposure happens the same way, top to bottom, so that each pixel is still exposed for the same amount of time.  Data is then read out in the same sequence as soon as exposure is completed.  The name comes from the “rolling” effect of how each line is turned on sequentially. 

By nature of their underlying architecture, CMOS cameras are inherently rolling shutter devices.  It’s part of what makes them very fast, and very low noise.  When exposure times are extremely short, CMOS cameras can start taking one picture at the top of the sensor while the bottom of the sensor is still reading out data.  Some CMOS cameras also have special electronics to allow them to function in a global shutter mode.

In very fast samples, a rolling shutter can create bending or waving artifacts. Sometimes this can be prevented with synchronized or strobed illumination, or fixed with software.  Sometimes the tradeoff of very high speed makes it worth dealing with the imaging artifacts.  But other times, switching to a sensor with a global shutter is the best option.

Let Us Help

The question should never be “CCD or CMOS”?.  The question should be “what are you doing with your microscope, and how can we get the best camera to match”?  Contact your I Miller representative to discuss camera details.  We’re happy to find the best technology that fits your specific imaging application.

For more information contact us at sales@imillermicroscopes.com or call 215-925-2285.

Look for Part 5 "Getting The Full Range" Coming Soon