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Old June 27th 04, 04:56 PM
Richard Ballard
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Default 50mm "normal" lens with digital SLR?

In article ,
(Richard Ballard) writes:

In article ,
Chris Brown writes:

In article ,
G.T. wrote:

Chris Brown wrote:

It's very, very simple.

The more I read this thread the more confused I get.

35mm is the "standard" focal length for that camera.

I thought I read someone's calculation that 28mm is.

Well, the actual "normal" focal length is bewteen the two,
and there's not a
lot of difference between them, so either will do the job.

In 35mm film photography there is sufficient difference
between the coverage (and fisheye distortion) of 35mm
and 28mm lenses to justify offering both these lenses --
they are not identical.

As focal length decreases, each millimeter focal length
reduction becomes (percentagewise) increasingly significant.
In some ways, longer focal length lenses are more forgiving
of (a given amount of) imprecision.

I have read this thread with some amusement because
I believe you are arguing the wrong issue.

"Normal" relates imaged scene coverage to human vision coverage
(i.e., what a human views normally using their eyes), while the
imaged scene coverage of a given focal length lens depends upon
the digital SLR's sensor chip area. A smaller focal length lens
coupled with a smaller sensor chip (and appropriate camera
dimensions) gives the same imaged coverage as a larger focal
length lens coupled with a larger sensor chip (and appropriate
camera dimensions). Using a film analogy, the normal (nominal)
50 mm lens used with 35mm SLRs would _not_ provide normal
coverage were they used with a 2"x2" format (type 120 film --

Before somebody jumps down my throat, I know that type 120
film has a (nominal) 2.25" by 2.25" coverage area. Obviously
I never owned a Hasselblad.

e.g., Hasselblad) SLR. 35mm film is one sensor standard and
2"x2" film is a different sensor standard -- different "normal"
lenses for different sensor areas.

Digital photography is not yet fully mature. The different dSLR
manufacturers have not yet agreed on a common sensor size(s).
(The analogous situation is different SLR manufacturers having
different definitions for 35mm film coverage area -- some mask
portions of the 35mm frame to hide lens flaws.) IMO digital
photography will _not_ be fully mature until manufacturers agree
on sensor size. Then industrywide standards will develop,
component commonality will occur, and economies of scale will
drive down digital photography equipment costs. dSLR
manufacturers will compete in the areas of optics quality,
man-machine interface (ease and flexibility of use -- think of the
VCRs you never learned to program), provided features, and
dSLR durability/maintainability.

Sensor quality will become less of an issue because most
manufacturers will utilize the same sensor chip -- a high quality
product made affordable by manufacturing economies of scale
(just like photographic film).

An analogous situation already exists in the computer industry,
and (IMO with some justification) a person can view a dSLR
as a special purpose computer.

'Hope that helps.

Richard Ballard MSEE CNA4 KD0AZ
Consultant specializing in computer networks, imaging & security
Listed as rjballard in "Friends & Favorites" at
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