| |
About 30 years ago, researchers tried to replace the heavy, slightly whirring 16 mm cine cameras by TV cameras – then also rather heavy. The movement of tiny organisms could now be shown “live” to many spectators. Moving pictures could be recorded on magnetic tape, which made the handling of photo documents much more easier. Only the so-called “C-adapter” has remained from the days of the cine cameras. The first TV cameras had one thing in common with the cine cameras: The pick-up tubes had an outer diameter of one inch, but an active target for image recording with a 16 mm image diagonal – identical to the film. TV cameras could therefore be attached to a microscope via the same adapter as cine cameras, namely via the C-adapter.
The tube technology is now a thing of the past, although it has survived in the names of the modern CCD sensors. Nobody could say that any part of the 1/2” CCD sensor actually is 1/2” in size. This all becomes clearer, however, when we remember the tube with the outer diameter of 1/2”, the target of which was only 8 mm in the diagonal.
There is one thing, however, which the new semiconductor sensors have in common: their active areas are very small (1/3” CCD: image diagonal of only 5.3 mm). And that is where the problem starts: If these sensors are inserted directly in the intermediate image, they record only a fraction of the image visible in the eyepiece, i.e. only just about 4% in the case of the 1/3” sensor! Things were much easier with the good old 1” tube camera, since the image diagonal of 16 mm permits a good 37% of the area to be picked up in an intermediate image.
This means that the trend is the very opposite to that of photomicrography, where the image had to be additionally magnified by the factor 2.5x on account of the film size (diagonal: 43 mm).
Today, optical adapters are required if we want to see object sections which are bigger than a postage stamp. Absurdly, what has to be done is to reduce the size of the intermediate image which we have just magnified with such difficulty. Of course, color fidelity and resolution of the image should be retained, which means complex optics in the TV adapters. On the whole, the inevitably large adapter and the wonderfully small CCD camera sometimes combine to form units of a considerable size.
Meanwhile, some changes have taken place in videomicroscopy. Although TV microscopy is still used in lecture rooms for simultaneous observation by hundreds of viewers, CCD cameras, connected to video printers, are now much more widely used because this combination provides a fast and neat alternative to instant photography. Even the digitization of TV images for further processing and storage in computers has become very budget-priced. The trend regarding electronic image sensors in microscopy is moving away from the (lowprice) TV camera towards the “Slow-Scan CCD sensor” which is more like a digital photo camera. The reason is evident: Why read out 25 or 30 images every second if still picture videography is of the essence? A somewhat slower scan, but with higher precision, with less noise and better resolution is then to be preferred.
Top | |
|