|
Quote:Mike Mills
I have never yet seen a commercial optic that approaches the
limitations of the laws of physics in a commercial camcorder
selling for circa $1k. What is your real point? .
I completely agree with your statement. The optics are indeed inferior to the best possible, probably by a factor of 2 or 3. The question however is simple: is the current resolution of a $1k commercial CCD camera limited by optics or by the CCD? If its the CCD, then to improve image resolution (fine details) you need to improve the CCD; that's what they appear to believe in all the reviews on this site. On the other hand, if its the optics, then you need to choose the camcorder with the best optics. Assuming of course you want clear, sharp images with as fine a detail as possible. Current $1k CCDs have pixel size down to about 3 microns, but the Airy disk (the spot of smallest possible light concentration) is around 4 microns for a 10mm lens. We agree the lens systems are less than perfect so the Airy disk is more like 10 microns. Now that means that a good CCD will spread several pixels across the Airy disk and thus the resolution of a camcorder is limited by its optics and NOT by CCD pixel size. Getting a better CCD will NOT help make images sharper. However a better lens will make the Airy disk smaller and thus produce sharper images. Now the Panasonic gs200 has a lens size of 8.75mm which produces an Airy disk of 10 microns. But the Sony hc85 has a 21.4 mm lens which produces an Airy disk of about 5 microns, which will result in a sharper image IF you have sufficient magnification and IF the light loss due to magnification isn't too great. The Panasonic gs200 has an F# of 2.8 at full zoom which not only reduces the amount of light coming into the CCD but it also happens to be above the F# necessary to cause diffraction to become significant and which then increases the size of the Airy disk. In contrast the HC85 operates at f2.1 which gives a 70% brighter images and which is below the diffraction limit so its Airy disk isn't affected by zooming. In addition the HC85 has a longer zoom focal length so its images will have more magnification. More magnification means you can actually see the details (resolution) that your optical system is providing. And with a larger lens the hc85 can provided the light necessary to actually see the image at high resolution. In other words the gs200 actually has worse resolution and dimmer images as you zoom to maximum while the Sony gets better. The result will be sharper zoomed images in the Sony product compared to the gs200. The same is true for the gs400 because it has a lens 1/2 the size of the HC85. Canon products will similarly out perform as well. So my point is simple. It's not just the CCD size that's important, it's also the optics. And these review say almost nothing about the optics and certainly don't give you the information necessary to calculate the objective lens size. In fact they don't even test the zoom resolution at all. Instead they marvel over a gs200 700x digital zoom and lament the HC85 having a mere 120x digital zoom. (both of which are pretty marginally useful at best). My intent was to point out to the reviewers and users that more emphasis should be put on optics and less on CCDs. At one point a review wonders why the more expensive Canon Optura 40 is even necessary because it merely provides a slightly bigger zoom compared to the Optura 30. But they missed the whole point. The Optura 40 has a bigger lens for more light gathering and better resolution on zoom. That's why you are paying more. Then they pour praise on the gs120 because it has 3ccds and is so cheap...what a bargain! However they don't even note that the gs120 has a tiny lens (8.75mm) which is the reason it can be so cheap (its expensive to make optics better and cheap to make CCDs better). If a small lens didn't matter that would be kewl, but it does matter; you can't beat physical laws. So why bring this all up? Well I am looking for a new camcorder to replace my 12 year old model. My old camcorder has a 24mm lens and I was surprised to find so many models recommended that have small lenses. I decided to see if the small lens really didn't matter with todays super CCDs. Well, after some study it seems that optics still do matter. I will be getting a Canon or Sony product with as large a lens as I can afford. I would avoid Panasonic until they bring their optics up to the standards of the others. Get it now? ps: I will say that so far I haven't been able to understand how a digital 1+ meg image is translated into miniDV format and ultimately how that affects the final resolution on tape. It is possible that so much resolution is lost in the final jpg conversion that its the miniDV format that needs to be improved and that the CCD and optics aren't important at all. At some point the flow of information from the CCDs will exceed the capacity of the miniDV format. When that happens, or if it has already happened, I haven't been able to discover, yet.
|
|