OK, I found a neat dejanews article by Chuck Olson.
where he showed how you could find out the effective diagonal CCD size by using available information from the camera manufacturers. What you need is the actual focal length (AFL) of the camera (usually written on the lens or in the specs) and the equivalent focal length (EFL) compared to a 35mm camera. EFL is trickier to find but you will often find it published by manufacturers. They use it to help people understand the "power" of the lens in 35mm terms which are more familiar to people (ie. what power is equivalent to a 50mm lens.)
Firstly, the diagonal size of a 35mm negative is 43.267mm or 1.7 inches.
The relationship is simply a geometry relationship determined by this equation:
EFL/43.267mm = AFL/CCD size (in mm)
solving for CCD size and converting to inches we get:
CCD size (in inches)= 43.267*AFL/(25.4*EFL)
Using this on my brand new old Ricoh 18H/Sony TR101 was an eye opener. The focal length of the 18H/TR101 was 6.2-62mm (hence the 10x zoom) which Ricoh says is equivalent to 45-450mm in 35mm terms. That gives me an effective CCD size of only .235 inches. That appears to say that the old 18H/TR101 used a 1/4" CCD like modern cameras! This would blow a hole in the theories that new cameras are worse than old cameras because of their smaller CCD's.
Before we jump to that conclusion, though, it is important to understand a few things.
Firstly, it is doubtful that any 1/4"CCD actually uses all its 1/4" of CCD. In fact, when Chuck did the calculations for a supposedly .588" CCD camera he found that it was only using .37 inches (Fuji MX-700.) This is probably similar to the whole monitor size vs. effective size issue. Manufacturers might be measuring the size of the CCD chip vs. the image size the chip can support.
So it quite possible that the 18H/TR101 is using what was defined as a 1/3" CCD.
Secondly, most of the modern cameras (like the TRV I reviewed) use electronic image stabilization. This means that while the lens is projecting the image across the whole CCD, the camera is only electronically using a portion of the image. This portion is constantly juggled around to steady the image. Effectively, the camera is throwing away some of the light it has gathered.
The 18H/TR101 uses optical image stabilization. This uses a mirror to keep the image steady on the CCD surface and uses all the CCD surface.
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Now, here's what I've found so far on focal length, aperature and f-stop and their relationships.
F-stop a measure of how much light a lens lets in. Equivalent F-stops let in equivalent light. Therefore, a lens with an F-stop of 1.2 lets in more light then one of 1.4 or 1.6...etc.
F-stop is simply a measure of how large the lens can open. It is defined by this simple equation.
F-stop = Focal length/Aperature size (dia. of hole that lets light in.)
Now the relationship of F-stop to light gathering is logrythmic (spelling?) Fortunately, camera manufacturers have documented this (so we don't have to calculate it) and have put the increments on the side of lens (at least on 35mm lens.) Take a look the lens on a decent 35mm camera and you will see a scale that goes like this, 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16...etc. This scale is marking each halfing of incoming light transmission.
With knowledge about F-stop we have "half the equation." The other half is how much of that light is actually used by the device that captures the image...how efficient is it. With photographic film this is measured as film speed. With 35mm cameras you can use faster film to make up for less light (at the expense of grain size.) For video cameras the manufacturer can try to make a more sensitive CCD but very quickly reaches the limit of the technology. To further boost the image the manufacturer electronically amplifies the image (gain.) This is the biggest difference in modern cameras vs. older lower lux cameras of years past. The manufacturers have added higher gain ranges to their cameras effectively boosting the low light abilities of the cameras. Unfortunately, this post acquisition, boosting only makes for a recognizable image (the detail and color saturation, once lost, can not be returned to the image.)
Now what does this have to do with modern, minaturized camcorders?
An easy way to get lots of zoom is to create a small lens with a large focal length and ensuing poor speed.
Point and shoot (P&S) cameras with their large zooms and small lens diameters (and the ensuing high F-stop numbers) have become very popular using this strategy. P&S's have been able to get away with this because fast film technology has made quantum leaps over the last century.
Video cameras are going in the same direction.
Unfortunately, there does not seem to have been the same quantum leap in CCD technology or at least not in the CCD's they are putting in the cameras of today.
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Trying to compare the old RCA to the 18H/TR101 and TRV series.
Unfortunately, I can't find anything in the RCA literature to compare its AFL to it EFL. But there is one big difference between the RCA and the Sony and that is lens speed. The RCA is a F1.4 lens, the 18H/TR101 a F1.6. I don't know the scale below F2 but I would guess, based on the logrythmic nature of the scale, that a F1.4 lens is considerably faster than a F1.6 lens.
Also, the RCA lens is bigger than the 18H. Bigger lens grab more light (That's why professional telescopes are so big.)
This is actually, where it gets tricky. Why is a video camera lens smaller than the equivalent speed 35mm lens? The reason is that the image projected is much larger for a 35mm lens, therefore more lens is required. Remember, equivalent F-stops yield equivalent light measured in lumens/area. The area of the 35mm negative plate is larger therefore it requires more total light (more lens.)
Using a smaller CCD lets manufacturers use smaller lens. Here it is important to remember, that, even though the light per area is the same on the smaller CCD it has gathered less light (information) because it is smaller.
Therefore, all thing things being equal, a larger CCD camera will have better light performance. As light levels lower, light gathering becomes more important.
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I hope to clean up and flesh up this information as time permits. Any feedback is appreciated. Please email me with your comments at dlauring@hotmail.com.
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