just give your friend the URL for
http://www.luminous-landcape.com
There are some good film vs. digital comparisons there. Your
friend is quite mistaken if he thinks ISO 200 gives him 30MP of
real data.
He sure is. It undoubtedly gives far more than that. Don't underestimate film.
On the other hand, don't overestimate your lenses, either. They are the real bottleneck in this equation, not the film. While it's certainly possible to make quality distinctions between different films, most modern emulsions are capable of capturing more data than what's produced by even the best lenses.
It's important to recognize that there is a difference between "human perception" and measureable data. In most cases, any perception of digital as being superior to film is almost entirely based on other factors besides how much data is being captured.
First among these factors is signal to noise ratio. In a digital camera, the "noise" manifests as variations in the image sensor's response to light. The more variations there are and the more greater their magnitude, the "noiser" the image is.
In a film camera, "noise" is the film grain. However, the fact that film grain comes in a variety of sizes, even within the same image, makes it somewhat more difficult to measure in precise terms, as does the fact that grains of film ALSO have some variation in their response to light.
Digital cameras may not capture as much detail as film, but they produce data with an extremely good signal to noise ratio. Part of the reason for this is the fact that they do not capture what would be considered "high frequency" data. That's signal-processing terminology that translates here as fine image detail.
With a digital image sensor, you can only capture fine detail up to a point defined by the image sensor's resolution. Because the size, position, and number of pixels are fixed, the nature of the image sensor acts as a sharp cut-off filter for fine detail, and any detail beyond that point is lost.
With film, the average grain size (and shape) is the limiting factor on how much detail can be captured. But since grain varies a lot in shape and size, there is no hard cut-off point like with digital. Very fine detail does not get filtered out the same way and it can still be captured. On the other hand, the "noise" of the grain also becomes more and more prominent at the same time.
As far as human perception goes, signal to noise ratio is usually more important than ultimate frequency response (the amount of detail being captured). For example, most people would rather watch a clean regular TV signal than a real snowy HDTV signal.
Likewise, unless the difference in image resolution is REALLY obvious, a noise-free digital image will generally be perceived as superior to a somewhat noisier film image, even though the film image may have more detail hidden amongst the noise.
Mike
