On Sep 11, 2005, at 8:23 PM, J. C. O'Connell wrote:
If I am getting what you are saying, you are talking
about a special optical device BETWEEN the image forming
lens and the sensor. If that's what your talking about
then yes that would always be "active" but we havent
been discussing something like that, we have been
discussing an image forming camera "lens" and they do NOT do that.
What your talking about is more like a secondary otical
system in addition to the "lens"
Yes, that's what a dedicated digital sensor lens design is, in
conceptual terms. It's what the Sony R1 lens is almost certainly like
if you look at the ray trace.
Secondly in the case of a camera "lens" the size of
the rear element has little to do with "active area"
or percentage of its area in the optical path.
You're the one who was talking of "active area" vis a vis the rear
elements. I'm just trying to use your terminology.
well this makes no sense to me. enlarger lamp houses
convert the bulb (point) source to a large parallel
cylinder of light to illuminate the negative evenly.
A "large parallel cylinder of light" is the same thing as light
coming from an infinitely distant point source. Consider light from
the sun: all rays are parallel at 92 million miles distance, unless
scattered by atmosphere. In the vacuum of space, they are absolutely
parallel. So even though the sun is several hundred times the
diameter of the Earth and is a light source, it is a point light source.
a camera lens forms an IMAGE, the raya coming out of
a camera lens towards the film/sensor is diverging
to form an image. If you had a camera lens in an enlarger
lamp house your would get an IMAGE of a light bulb illuminating
the negative which would of course be terrible.....
It's an analogy, JCO. The nodal point of a lens is that dimensionless
point through which all the light paths intersect. It is, from the
point of view of the focal plane, the same as a point light source.
The fact that the light rays which intersect there are coming from
spatially different places and are of different intensities is
inconsequential to their trace path. Fagehddaboudit.
yes but its WORSE because with 35mm FF or film cameras
All normals and even slight wide angles can be done
without the need for retrofocus. With APS sensor in
camera with same 45.5 mm registration, even normal
lenses (~30-35mm on APS ) have to be retrofocus as well as all wide
angles
its worse not better to have the flange so far away on such
a small sensor. The closer the better on ALL cameras
all else being equal because it give the optical designers
more options- like this new non SLR 10MP camera we
are talking about.
Since most of the best short lenses now in existence are now inverted
telephoto designs (even for rangefinder cameras with a 29mm register
like the Leica M), return both resolution and contrast comparable to
or surpassing the best non-inverted-telephoto, and better evenness of
illumination, I would consider the distinction to be moot. The price
for this is more complexity in lens formulae and more complexity in
construction, but we seem to have overcome the technical challenges
required.
Godfrey
