How to select a digital still camera

1. Resolving power required by the CCD

Resolving power d of the image passing through the optical system of the microscope and reaching the CCD of the digital camera is expressed in the formula d=1/(2*f) and f=2*NA/ λ.

• f: lens cut-off frequency

From the above formulae, d= λ /(4*NA). Here, λ is 550nm (the wavelength at the center area of the visible light).

NA is the NA of the lens closest to the CCD of the microscope optical system divided by the magnification, and this resolving power controls the overall resolving power. In the optical system of the microscope, this NA is greatest in a low-magnification lens. At present, the maximum value of NA is perhaps about 0.04. If this value is used to calculate resolving power, d = 0.55λ/(4*0.04) = 3.43 λ. Therefore, resolving power required by the CCD = 3.4 λ.

d = 0.55λ/(4*0.04) = 3.43 λ. Therefore, resolving power required by the CCD = 3.4 λ m.

If the pixel pitch of the CCD used in the camera is on the order of 3.4 λm or less, the image of the subject is sufficiently resolved. A CCD with square pixels of 3.4λm is used in the Nikon Digital Sight DS-Fi1/Fi1c camera heads.

• Digital Sight DS-Fi1/Fi1c camera heads

2. Image refresh rate

Depending on the image from the digital still camera, the image needs to be refreshed in a short time when the focusing or angle of view is adjusted. Generally, moving pictures require 30 Hz and quasi moving pictures require 15 Hz. In the case of digital still cameras, the speed at which data is read from the CCD is limited. If the number of pixels is large, image reading time is generally slower. As a way of overcoming this limitation, the CCD has a mode that thins the data so that it can be read more quickly. The general way of using a CCD is thus to make focusing and angle of view adjustments based on this thinned image, and to use high picture quality when shooting the picture.

The Nikon Digital Sight DS-Fi1/Fi1c camera heads input an image equivalent to SXGA quality at 7.5 Hz from the CCD, and can store the full 5M picture while displaying it on the LCD at the front or on an optionally available display. (Sensitivity correction and other adjustments when the mode is changed are all automatic.) In our estimation, we are able to achieve a balance here between the definition of the displayed image and a moving- picture-like frame rate.

• Digital Sight DS-Fi1/Fi1c camera heads

3. Equipped with standard PC interface

There is a growing need to export images to a PC in order to store them, analyze them, or even send them to people around the world. In the past, a dedicated interface board was required when exporting images to a PC, but nowadays, PCs come standard equipped with interfaces such as LAN Ethernet or USB.
The Nikon is equipped with both LAN Ethernet and USB ports for easy connection to PCs.

4. Ease of use: It is equipped with operating methods compatible with the various observation procedures on a microscope

As with general digital cameras, if the photographer does not adjust shooting conditions to suit the various observation procedures of the microscope, it will not be possible to achieve desired results. Nikon believes that an easy-to-use camera must be able to accommodate the microscopes various observation procedures.