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Add video to your microscope for even better imaging.

Good things come in small packages, so the saying goes. This particularly applies to small video cameras, whose shrinking size and increasing performance are bringing a lot of good things to today's microscopist.

Improvements in video detectors and peripheral equipment over just the past two years have made dramatic improvements in the microscopists' ability to image samples. With video capabilities, you're not restricted by fixed optics anymore. You can use handheld video microscopes that magnify up to 1,000 times samples that were impossible to place under conventional objectives.

You also have more choices for storing and reproducing images than with conventional photographic methods. And you have a multitude of image enhancement, manipulation, and digitization capabilities.

Best of all, you don't have to strain your eyes peering through an eyepiece all day. A video camera even gives you the ability to fully automate or operate remotely your microscopy system.

But, selecting the primary components of a video system--the camera, display, image storage device, and reproduction devices--requires that you make a lot of tough decisions about the type of information you want to get from your image. You need to select the type of camera that best fits your imaging needs and determine its image contrast and resolution requirements. You also have to select a matching display system and ensure that your storage and hardcopy devices are compatible with the rest of your equipment. Last, but not least, you need to determine how much you're willing to spend.

"Video cameras, video hardcopy devices, and even some microscopes are changing so quickly that you may even need a systems integrator to sort through all the vendors and products that are available," warns Lee Shuett, manager of biomedical microscopes, Nikon Instrument Group, Melville, NY. "One system integrator, who can filter through all these vendors, is your local microscope distributor."

A video microscopy system begins with the optical microscope. "It's pointless to talk about video systems and equipment until you decide what kind of optical system will solve your problem," says Shuett. The optical system drives your choices downstream, because it determines light levels, resolution, contrast, image size, and type of storage device.

"Optical systems with the best possible resolution are confocal laser scanning microscopes," says Bob Fasulka, industrial products manager for Leica, Rockleigh, NJ. Confocal microscopes illuminate a single point at the focal plane of a sample and then reflect only that information back to the detector.

"Computers also allow us to optimize the design of objective lenses and coatings," says Fasulka. "Apochromatic lenses are specifically coated so that all of the visible wavelengths are focused to one plane, which produces a much sharper, higher contrast, more well-defined image. This pushes resolution of the image to the maximum possible amount."

Microscope manufacturers also are redesigning their products light transmission. "One method is to reduce the number of optical elements and another is to shorten the light path lengths," says Peter Dorogi, manager of biomedical products at Carl Zeiss, Thornwood, NY. "In some cases, we've eliminated up to one third of the lens elements in a 30-lens assembly.

"With these types of improvements, we've been able to obtain about 30% better light transmission in our microscopes, such as in our Axiovert 100 and 35 models, over the past three years," says Dorogi.

Unfortunately, video cameras are still playing catch-up with optical systems of the 1950s. "Current optical microscopes have about 10,000 times the resolution of current video cameras," says Leica's Fasulka.

While improvements in video camera resolution will narrow that gap, the optical-video differential in five years will still be about 1,000 to one, forecasts Fasulka.

Acknowledging that limitation, once you select a microscope you need to determine the video camera that is best suited for your imaging needs. Video cameras come in two types--color and black and white. They also come in two styles--vidicon tube and solid-state versions.

The first cameras mounted on microscopes were vidicon tubes, such as those manufactured by Dage-MTI, Michigan City, IN. Typical 1-in.-dia (2.54-cm-dia) vidicon tubes deliver about 800 to 1,100 lines of resolution and cost $1,500 to $2,000. These systems, however, are bulky and expensive compared to solid-state devices.

Solid-state cameras contain charge-coupled devices (CCDs), most of which are made by Sony, Teaneck, NJ. While CCDs are smaller and less expensive than vidicon tubes, they often don't have their resolution.

CCD cameras with 0.67-in. (1.7-cm) detectors have 500 to 600 fines of resolution.

"There are 1,000- to 2,000-line black-and-white CCD cameras, but these high resolution cameras cost about $15,000," says Nikon's Shuett.

When selecting one of these cameras, you should note how faithfully your choice reproduces the contrast of the object being imaged. This characteristic is referred to as spatial frequency. CCD cameras are very good at reproducing spatial frequencies equivalent to those of the human eye. "The display from a CCD camera looks spectacular, but the images are diffraction limited," says Shuett. "You cannot increase the gain on the CCD, which means that the vidicon tube will give you a better image from which to obtain information.

Just like black-and-white cameras, color video cameras come in both vidicon and solid-state versions. The solid-state CCD versions are available in one- or three-chip configurations.

The low-light performance of color CCD cameras has improved dramatically over the past three years. "Current one-chip cameras operate at very low light levels, which means that for color intensive applications such as those in the metallurgical field involving differential interference contrast (DIC) with a Nomarski effect, they are extremely valuable," says Joseph Oppenheim, product technology manager at Buehler, Lake Bluff, IL.

"The extra optics and prisms involved in DIC imaging still transmit enough usable light for the low light level CCD to detect, even at 1,000 x," he says. "The high magnification and the Nomarski effect provides a very good test of the low light level performance of solid-state and vidicon tube cameras."

Most video cameras, both vidicon and CCD, are packaged in a box containing their electronic controllers. This box then is mounted directly on an access port of the optical microscope. A few companies package the controller electronics separately, so that the video head can be mounted on the microscope without taking up a lot of space or inducing stray loads into the microscope.

"Low-light versions of this configuration also are available," says William Burroughs, director of marketing for Optronics Engineering, Goleta, CA. "Our VI470 single chip camera can detect down to 0.005 LUX which is useful for true color imaging of fluorescent specimens.

Three-chip CCD cameras offer higher resolution, but at increased cost. While a $15,000 cost may be acceptable for medical applications, it is too expensive for most industrial research applications. Current three-chip CCD cameras have up to 900,000 pixels/chip with 800 horizontal lines.

Two standards are used by U.S. firms for color video displays--NTSC (for the National Television Standards Committee) and RGB. For black and white the standard is RS170. These standards define how many video scan lines are displayed.

"It's extremely important to match the resolution of the video display, or monitor, with that of the camera," says Buehler's Oppenheim. "RGB displays are a little more expensive, but the color rendition and sharpness are generally worth it."

Nikon's Shuett agrees. "One signal on NTSC generally is never the same color twice," he says. "RGB is better." NTSC displays cost from $250 to $500, while RGB displays cost from $700 to $1,000.

There has been some trickle down in monitor improvements from high definition TV research. "There hasn't been a lot, because there's no standard yet," says Shuett.

The major problem with video displays is the lack of 3-D imaging capabilities. Many microscopic imaging applications, such as those in semiconductor analyses, traditionally are performed with stereo microscopes to obtain information on spatial relationships. Micromanipulation of the video-viewed sample also is difficult because it lacks 3-D views.

There are several systems that attempt to produce 3-D images. One system from Stereo Graphics, San Rafael, CA, uses special viewing glasses that, with electronics, alternately switch on and off each viewing lens while viewing the same object on a monitor. The flicker is so fast that you don't notice it, but you do get a 3-D visualization of the display as your brain tries to recombine the phase-changed images from each eye.

Another system uses an electronically switched, layered LCD screen to give a 3-D effect. A third complex system transmits two different signals, which are then processed through an electronic shutter. All of these 3-D systems are expensive and limited in their performance capabilities.

The equipment used to capture and store video images is limited in the amount of information that you can work with and store. Storage systems, such as magnetic disks, optical disks, and tape systems, often have capacities that are less than that of one high-resolution picture. One black-and-white image can require about 1.2 MB of space on a magnetic disk. For higher resolution, images are stored on a low-resolution storage device and reproduced as low-resolution images.

A way around this limitation is to go back one step and take a 35-mm photograph of the monitor image. The photograph then can be scanned and digitized at up to 6,000 lines. This information can then be mapped, stored, and manipulated.

"Reproductions of black-and-white images on current printers don't have the resolution of instant film reproductions but for many applications they are good enough," says Oppenheim. "A Fortune 500 company in Illinois made 2,000 instant film images per month at a cost of 85 cents a copy. Using a video laser printer, the company was able to reduce the imaging cost to about 11 cents each."

Leica's Fasulka believes that video imaging systems will take the place of instant film in many applications, including that in metallurgy. "Video printing can make instant film disappear," he says.

There are various manufacturers of black-and-white video printers, such as Sony, Mitsubishi, and Sekosha. The latest versions are third-generation products and cost about $1,500.

The biggest problem in a video microscopy system is the lack of a high-resolution "The performance of color cameras and even color monitors has leapt ahead of that for hardcopy printers," says Nikon's Shuett. "You can spend $10,000 on a high-resolution camera and $5,000 on a matching monitor, but unless you just want to sit there and look at the monitor images, you can't do anything with them."

The few color reproduction systems that match the resolution of the color camera cost $20,000 or more. "High-resolution video printers are at same place where instant years ago," says Leica's Fasulka.

The lack of a high-resolution color printer limits the usefulness of video microscopy systems; however, if improvements continue in this area as they have for the past two years, this problem should be resolved.

Video Microscopy

For more information on equipment used in video microscopy, circle the appropriate numbers on the Reader Service Card.
Buehler                        379
Kohu                           380
Leica                          381
Nikon                          382
Olympus                        383
Sony                           384
Zeiss                          385

Space limitations preclude listing all manufacturers of these systems. For further information, see the R&D Magazine Product Source.
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Author:Studt, Tim
Publication:R & D
Date:Jul 1, 1992
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