Winsor Crosby wrote:
"Isn't there some conventional wisdom that the larger the sensor the
less digital noise? There was also something somewhere that the
reason that Nikon and Canon were using the large sensor, besides
preserving peoples' lens collections, was that no one has figured out
how to design an ultra wide angle for a small sensor yet? So anyone
used to shooting with a 21mm would be out of luck with a small sensor
camera?"
It's certainly true that a large sensor with large pixels will have a lower
noise level. Or to put it another way, shadow detail will not be swamped by
noise, and the equivalent film speed can be higher for the same reason. It's
all down to how many photons can be collected, compared to the 'false' signal
generated within the sensor itself.
I don't know any reason why one couldn't design a super wide angle lens for a
small sensor. But I would make some technical observations regarding apertures.
First, there's the mechanical difficulty of making nice round small dimension
apertures for the short focal lengths, and making them stop down consistently
when the photo is taken.
Second there are diffraction effects from small apertures. Even a standard 50mm
lens is said to be diffraction limited from about f/8 down. This due to the
absolute diameter of the aperture, not its relative diameter (f no.). So small,
short focal length lenses will hit diffraction limits at wider f numbers.
Third, there is depth of field. Because you are scaling down the camera
relative to the real world, for a given f stop, the depth of field will be
larger for a small sensor system than its equivalent lens/aperture in a large
sensor system. We see the same effect in reverse going from 35mm to larger
formats - you need to stop down more to get the same depth of field.
This great if you're into landscapes, but not if you are into portraiture.
If Olympus marketed a digital camera with physically small bodies and lenses,
that could perform as well as 35mm film, would I buy it?
You bet your Asahi.
Chris Barrett
Malvern
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