Less is More??

[Dennis Hull]

Someday I really will buy either VX2000, PDX10 or GL2. Also, I have researched posts and read posts in this forum on CCDs but an article (page 55) in Oct. 2002 "Camcorder and Computer Video" seems to put slightly different slant on CCD size and pixel count. Discussing large CCD's vs smaller higher pixel count CCD's article says "the smaller the pixel the less dynamic range it can provide" impacting ability to handle differences in contrast between light and dark. Article also says " the number of pixels alone is not a good indicator of the cam's image quality or color reproduction. A camcorder with a 1/4 inch CCD with 480,000 large pixels will produce better images than another camcorder with a 1/4 inch CCD with 680,000 smaller pixels." Not intending to quote anything out of context, it sounds like another reason to consider larger and lower pixel count CCD's of VX2000 vs GL2 and PDX10 smaller, higher pixel count CCD's is not only better low light capture but better image quality (as subjective as that can be) available from larger CCDs of VX2000. Is this "book learning" applicable or noticeable in real world experience??? I guess resolution or sharpness is different and affected more by pixel count than CCD size??

[Mike Rehmus]

All of it sort of 'depends'

As you know, if you multiply out 720 by 480 or even the 601 spec, you don't need all that many pixels. Just under 350,000.

So what do the added pixels do? They allow some image processing to take place where additional image information is useful. Some are used to replace 'bad' pixels. Some, in the digital anti-shake systems are used to allow the image to drift around on the chip to offset camera movement.

The size of the CCD has very little to do with dynamic range unless they have some new physics since I used to make digital cameras. The size certainly has a lot to do with the sensitivity of the ccd. I'm talking pixel size, not chip size. The reason is, just like film, the larger the sensitive site (a pixel for the CCD) the more photons it can capture for a given level of illumination.

Dynamic range is more a factor of the technology used in the sensor. CCD's tend to be limited to around 10 to 1 max. Photodiodes are quite a bit better but they require a great deal of illumination. Phototubes can be even better and more sensitive but noisier.

CCD range is limited by how much of a charge one can place on the receptor area of the pixel and by the amount of self-noise in the CCD itself. To get a better dynamic range, one has to cool the CCD to reduce the movement of electrons in the silicon. Astronomers do this with liquid nitrogen or some other liquified gas. I'm not certain which one is the current favorite.

In the future, CCD's may have a greater dynamic range by being made on Saphire or some other substrate. That might allow a higher charge on a pixel and perhaps lower noise. But probably not very soon except, perhaps, at the very highest end camaras. Like the 24 P HD cameras.

All things being equal, the overall size of the CCD does imply low-light sensitivity. But in the consumer/prosumer camera ranks, that rule of thumb is being diminished by the higher pixel counts for a given chip size. Hence the 950 is not as good in low light as the 900.

It is also dangerous to assign image quality attributes to large vs small CCDs. What you tend to find is that the larger CCD's tend to be put into more expensive cameras that have better image processing, higher quality CCDs, better lenses, etc. All of those factors can greatly affect image quality. As does the environment in which you operate the camera. A GL2 will deliver as good an image (probably) as a PD-150 in good light. In poor light, it is likely that the PD-150 will deliver a better picture than the GL2.

So, unfortunately, everything is interdependent and always depends on the context, the skill of the operator and even luck.

[Adrian Douglas]

This is exactly why we say go to a shop and test the cameras you are interested in and find the one you like the most. Buying a camera purely on specifications alone is not the way to go. Hopefully what Mike has written will answer a number of questions related to which camera has a better picture, better colour, etc.