[Leica] Re: Digital M??

[Jim Brick <jim@brick.org>]

First of all, 35mm cameras do not have interchangeable film backs. 
Hasselblad, Mamiya, Bronica, etc, MF cameras all have large removable film 
backs. View cameras all have (mostly all) removable Graflok backs that 
allows the attaching of any type of film back to the camera. Also, many 
film cassettes for LF cameras slide into the sheet film holder space and 
carry the roll film (Sinar, Horseman, etc.) outside of the back.

All of these cameras have a large enough back to house an entire digital 
camera.

They all also have a connector so that an umbilical can be attached to 
download images to a laptop or other digital memory device. Cheap smart 
media is basically useless with these backs. You need 1 gig microdisks or 
the like. Older backs had to send each image to the computer/memory device. 
You carry the memory bank in a case, over your shoulder like you would a 
Metz 60CT-4 strobe battery pack. Newer backs have enough memory (a gigabyte 
or so) to store several high resolution images before having to download 
them to a computer.

Many of the backs that fit LF cameras are scanning backs. They produce 
extremely high resolution but require very long exposures. 45 seconds to 
several minutes. Some MF backs are also scanning backs as the resolution 
obtained from a scanning back can be a quantum leap over a CCD matrix.

There are various mechanisms to synchronize a mechanical camera with an 
electronic back. But the bottom line is that all of these backs are very 
large and can house a ton of electronics. It is possible to synchronize the 
camera shutter for use with a digital back, but this is not the norm. All 
of the digital backs that I am familiar with contain their own exposure 
mechanism, as I have outlined before. A silicon substrate pulse to the CCD 
is the shutter. On backs for LF cameras, the shutter part of the exposure 
is also taken over by the back itself. The taking lens shutter is simply 
left open with the correct f/stop selected.

There are a myriad of ways of accomplishing this. Again, there is enough 
room and these cameras all have removable and replaceable backs. This is 
one of their strong points. Where 35mm cameras, except for a very few old 
cameras, do not have interchangeable film magazines therefore have no place 
to house all of the required electronics.

If you go here:

http://www.kodak.com/global/en/professional/products/cameras/dcsProBack/proBackIndex.jhtml

You will see that, built into this Hasselblad/Mamiya back is a full and 
complete digital camera including LCD preview panel. The film camera in 
front of the digital back is simply a dark box that holds a lens. As with 
other backs, this back controls the exposure. For use on a Hasselblad, 
either an electric Hasselblad or one with a CW winder must be used. The 
winder connects to the back and the exposure release also connects to the 
back. The back controls the camera. The camera is set on a longer exposure 
time than the digital back needs. This way the digital back will take its 
picture while the camera shutter is open.

Also, as I have said before, film camera lenses are too sharp for CCD's. 
Here's what Kodak says to do when a too sharp lens will cause artifacts:

For certain types of photography, you can mount the optional anti-aliasing 
filter over the CCD. The anti-aliasing filter dramatically reduces scene 
aliasing and moire. The anti-aliasing filter also has IR reflection layers, 
so an additional IR filter is not needed.

Basically dumbing down the film camera lens. Reducing the MTF to a value 
below the CCD pixel spacing frequency.

Jim





At 06:42 PM 4/30/2002 -0700, Joseph Codispoti wrote:
>Jim,
>
>over the past two years you have made abundantly clear that digital and film
>cameras do not mix. You have given us more information on the subject that
>could be obtained from other sources. And your prediction have indeed been
>proven true.
>
>I have a question regarding the same subject. How do the digital backs for
>unmodified Hasselblad , Mamiya 645, and view cameras handle the marriage of
>digital to film cameras? Although not exactly desirable, why could the same
>not be done for any 35mm camera?
>
>Thanks,
>
>Joseph Codispoti

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