Specimens which are suspended in water are not completely immobilized. Small objects will start to vibrate when one is tapping on the table on which the microscope stands. The optics of the microscope will magnify even the smallest vibrations. These vibrations become problematic when taking pictures with a photo camera which is mounted directly to the microscope. Both pressing and releasing the shutter button as well as the shutter mechanics itself can produce so much vibration that the image quality suffers. One can, of course, use a cable release or self-timer to improve the situation, but the shutter mechanics of the camera still cause considerable shaking. The effect of the vibrations are, naturally, more pronounced the higher the magnification in use. Permanent mounts (in which the specimens are immobilized) are somewhat less sensitive to vibrations, but the effect of a shutter release vibration is still there at higher magnifications.
There are several possibilities to reduce the vibrations:
Long exposure time: The microscope-camera system vibrates for the fraction of a second after shutter release. One should therefore use a long exposure time (2-5 sec.). The camera will therefore collect most of the light when the system is steady. Of course, this does not work for moving objects.
Very short exposure time: Alternatively the exposure time can be significantly reduced (about 1/250sec). This is so fast that the vibration will hardly be recorded. This requires much light, however.
Micro flashing: One can also use a flash system mounted above the light source. With experimentation, it is also possible to make a system like this oneself.
The cardboard technique: A similar technique is used in astronomy to make steady images. The camera is set to “bulb” (B) and the shutter is opened. The light intensity has already been adjusted, but the light source is covered by a dark piece of cardboard. The cardboard is then removed for exposure. This method is indeed free of vibrations but requires long exposure times to be practical.
Mirror lock up: Some digital SLR cameras have a mirror-lock-up function. The integrated mirror of the camera can be moved into an “up” position. This reduces the vibrations significantly because the mirror of the camera does not have to swing up during exposure.
Flexible camera-microscope connection: Here, the microscope does not carry the weight of the camera. Rather, the camera is mounted either on a tripod or on another separate system. A vibration of the camera is therefore not passed on to the microscope.
So what methods do I use? I use a combination of several measures: I use a mirror lock-up function, a self-timer (2 sec) and a “long” exposure time of about 2 sec. During the mirror lock-up, it is not possible to look through the viewfinder to focus. Focusing has to be done already beforehand, or one could use the live-view feature to focus and evaluate the picture on the LCD screen before exposure.