Choose Best Microscope Camera
Matching a video camera to your microscope can be tricky
In this lens I’ll discuss how to go about choosing a video camera for your microscope. Specifically, we’ll look at camera pixel array and sensor size and how it relates to the field of view and performance of your microscope. Basic video camera technology has been around for several decades. But it has only been the past 25 years or so that high resolution, high performance, cameras have become available, and costs have dropped enough to make them practical for everyday use.
CCD Image Sensor SizeFor the purpose of this article I’ll assume you are familiar with the concept of pixel array size and how it relates to the quality of the captured image. Typically as the pixel count in the camera’s imaging device (sensor) grows, the physical size of the sensor grows as well. However, the reverse is not always true. In other words as the physical size of the sensor grows, an increase in pixel count does not always follow.
For microscopy applications, a high pixel count is usually preferably, but just as desirable is a high light sensitivity. As the magnification of the microscope increases, the amount of light collected decreases. So increasing camera sensitivity can become critical. A common way to do this is to increase the size of the individual pixels, thus collecting more light.
As the size of the pixels increase and the number of pixels remains constant, the overall size of the camera imaging sensor must increase. This can lead to some confusion, so lets address that.
Let’s look at the ubiquitous standard color video camera. Developed decades ago for standard broadcast and closed circuit camera (CCTV) systems, they typically employ a standard image array size of approximately 640 x 480 pixels (VGA resolutions). There are of course much greater resolution cameras available today, but the VGA analog camera is wide spread, inexpensive, and supported by a huge array of accessories, including optics, image capture devices, imaging software, etc.. As a result, there are more of them in use for image microscopy than any other class of imaging device.
As manufacturing methods have improved, the size of the pixels and the overall size of the sensor, have been reduced. Smaller sensors cost lest to manufacture, so there is incentive driving the sensor size smaller. This has resulted in standardized sensor sizes of 1-inch, 2/3-inch, 1/2-inch, 1/3-inch, and even 1/4-inch. However, the 640×480 pixel count has remained constant.
When purchasing camera components Microscopists are faced with making a choice between these varying sensor sizes, and understanding how they will affect performance of their microscopes.
Hitachi KP-D20AAs an example, the Hitachi KP-D20A and KP-D20B are popular, low cost, high performance cameras for microscopy applications. The two models are identical except for the size of their CCD imaging sensors. The D20A has a 1/3-inch sensor, and the D20B has a 1/2-inch sensor. The D20B has higher sensitivity owing to its larger pixel size, but it costs approximately 30% than the D20A model. Which should a microscopist choose ? Well, it depends on their imaging priorities. Is high sensitivity more important than field of view or resolution ?
Microscope Camera Sensor SizeSo lets discuss how the physical size of the camera sensor relates to your microscope and it’s field of view. First, most microscopes these days include an auxiliary viewing port. The port can be used for a variety of accessories but is most often used to mount a video camera. You can mount a camera directly to this port, but the image relayed to the camera sensor is “raw”. In other words it is not adjusted optically in any way to match your cameras image sensor.
The image to the right, shows the circular microscope field of view in relation to a 1/3-inch and 1/2-inch CCD sensors as provided by the Hitachi KP-D20A and KP-D20B respectively. As you can see, the 1/2-inch CCD covers a larger percentage of the microscope’s field of view. In fact it overfills it, leaving a significant portion of the sensor, and pixels, outside the field of view. The superior resolution of the 1/2-inch CCD sensor is lost in this arrangement.
By comparison the 1/3-inch CCD is entirely encompassed by the microscopes field of view. One hundred percent of it’s imaging resolution is put to use to resolve the viewing field. Of course the down side is that a significant portion of the field of view is not imaged.
And there is the choice the microscopist must make when choosing a video camera. The rectangular dimensions of the imaging sensor is at odds with the circular nature of the microscopes field of view. The microscopist must prioritize sensitivity, resolution, and field of view to make the appropriate choice of camera.
As a result, most microscopists choose the highest resolution camera their budget will afford, and choose optics and sensor size to allow the entire microscope field of to be captured. Although a significant portion of the camera sensor goes unused, by choosing the highest resolution camera, the microscopist can balance image quality against information content.