OK so it's
all to do with magnification right? or no?
If so... again the 50mm lens's magnification is the same on any format.
What do you think. There must be something we're missing here.
A 5X7 crop pulled from a 20x30 print is the same thing as a 35mm crop
from a 4x5 image of the same focal length
so again... why? A lens's perspective or magnification just doesn't
change with image size.
Herschel
ADavidhazy wrote:
Good point.
I think the difference is that the record made on the smaller format
is enlarged more to get to the same final print size than the one made
from the
larger format record.
Another way to approach this it to agree that a 5x7 enlargement and a
20x30
enlargement should be viewed from different distances to be perceived
the same
in terms of perspective. If we agree on this then if a 20x30 is cropped
to 5x7
that portion of the 20x30 print should still be viewed from the same
distance as
the uncropped version of the 20x30 print and not from the distance that
the
5x7 print is viewed from.
No?
andy
the smaller format
Herschel wrote:
This is interesting although I'm not sure why
it should change with film-format. My little brain won't compute.
There seems to be some confusion between "Angle of View" and
"Perspective"
Surely a 50mm lens, used from the same camera position will give you
the same perspective (Converging lines etc) whether it's on a
Hasselblad as a wide angle or a 1.6-factor digital SLR as a short tele.
The only thing that's happening is there's more of it in the
Hasselblad.
In other words the 1.6-SLR is simply a crop of the Hasselblad image.
So why is this a factor in viewing distance?
Herschel
ADavidhazy wrote:
This has been posted in the past on this
list but did not include the reference
to digital cameras and their image sensors. So here it is again for
what it is
worth.
A Brief Comment on Perspective
In order to view a picture with the proper perspective, we wish to
preserve the
angular relationships between the original scene and the picture. As a
result,
we should view a contact print from a film camera, or a print equal in
size to
the dimensions of the sensor in a digital camera, at a distance equal
to the
image distance in the camera.
This distance is equal to the focal length of the lens unless the lens
is focused
on a close-up subject.
For accurate perspective an enlargement (a print larger than the
contact print or
sensor size) requires a viewing distance equal to the product of the
focal length
and the enlarging magnification. So, a magnified print from a 35mm film
frame to
5x7 inches and originally photographed with a 50mm lens should be
viewed from a
distance of about 5 inches / 1 inch where M then is 5x and so the
proper viewing
distance for perspective is 250 mm or about 10 inches. In the case of a
digital
camera with a 16x24 mm sensor from which a 5 x 7 inch print is made the
situation
is 5 inches / .66 inches and the M is then 7.5x and the viewing
distance for
proper perspective is 50 x 7.5 or 375mm or about 15 inches.
In both of the above cases the taking lens is assumed to be of 50mm
focal length.
And M stands for MAGNIFICATION or enlargement factor.
Quoted from "Introduction to Photographic Principles" by Lewis Larmore,
Director,
Advanced Research Laboratory, Douglas Aircraft Company. Dover
Publications, Second
Edition, May 1965. Updated to include digital cameras on 06-07-09.
Andy's extra comment: The consequence of this is that if we view a
print from the
"wrong" distance (as related to seeing a print in normal perspective) a
print will
exhibit "strong" perspective if viewed from too far a distance (usually
the case
when wide angle lenses are used) and "weak" perspective (usually the
case when
photographs with long focus or telephoto lenses are made) if viewed
from too near
a distance.
==== if you notice any errors in the stuff above please bring to my
attention ====
andy
|
