[Leica] not sure - but here goes

[Frank.Dernie at btinternet.com (Frank Dernie)]

Hi Mark,
on the off chance your question is not rhetorical here are a few reasons for 
the difference in price between small and large sensors being much bigger 
than thet between 35mm and 120 film.
Firstly the film is the same stuff, just a different shaped layer of plastic 
coated with the same light sensitive stuff.
In the case of sensors they are made on a wafer of silicone. The crystal 
structure of the silicone wafer has imperfections on it, and any chip etched 
onto a part of the silicone wafer with an imperfection won't work, so it is 
scrap. If, for example there is a defect every 2 inches, -all- 2 inch or 
bigger chips will be scrap, so that is the biggest sensor which can be made 
will be less than 2". Depending on how the layout of random faults and the 
sensor layout fall on a wafer, there will be a high scrap rate even on 
sensors less than 2". The scrap rate only comes down to negligible when the 
sensors are -very- much less than 2".
This means big sensors are expensive since very few few of those produced 
work. They are also expensive since the economy of scale is not there. Some 
are made by joining 2 smaller sensors together with software to "fix" the 
image at the join...
The technology for making the wafers is developing, so prices will come down 
eventually, but never to the film ratio.

Luckily, the sensor design of small and big chips is -not- the same, unlike 
film. With film, going larger format increases the potential quality by the 
increase in film area less the reduction in lens quality due to the larger 
image circle. Going smaller with digital the loss is -much- less than with 
film since the smaller sensors are -much- finer resolution than large 
sensors so the loss of quality is not nearly as much as it used to be with 
film.
cheers,
Frank

On 11 Sep, 2010, at 07:12, Mark Rabiner wrote:

> Brownie film does not cost that much more than 35mm film. Why should
> digital? Well it does. Bummer.