"telephoto" - another definition problem

a. Long focus lenses are physically as long as their focal length.
b. Telephoto lenses are physically shorter than their focal length.
The front element to film distance is shorter than the focal length.
c. Retrofocus lenses have the lens-to-film distance longer than the
lens focal length. Wide angles are usually retrofocus for 35mm SLR
because there needs to be room for the moving reflex mirror to clear
the lens.
d. 'Telephoto ratio' is the ratio between distance from front of lens
to film plane (f), and the focal length (l), telephoto ratio = f / l
e. True macro lenses are optimized to perform best in the range where
subject size rendered on film ranges from 1/5 lifesize to about 10x
lifesize. Higher than that, one enters the area known as
'photomicrography'.

wilt wrote:

a. Long focus lenses are physically as long as their focal length.

And their focal length can be considered long, i.e. longer than the focal
length that is considered "normal" for the format.
Otherwise they are "normal" or even "short" lenses.

His definition for "telephoto lens" was something very close to "a
lens
that gives a narrower field of view than a standard lens".


"That doesn't sound very wrong. In fact, not at all."

What about wide angle telephoto lenses, which were/are very widely used
on compact fixed-focal length film cameras? Most of these lenses had a
focal length of about 35mm with a vertex length slightly less than
that. IMO, any lens with a vertex length shorter than its focal length
is rightfully called a telephoto lens, regardless of the field of view.
Interestingly, some of the long EFL fast telephoto lenses have a
vertex length slightly longer than their focal length. For example,
the 200mm f/2 Nikkor is 245mm long, and the 300mm f/2 Nikkor is 359mm
long.

Brian
www.caldwellphotographic.com

Recently, BC posted:

His definition for "telephoto lens" was something very close to "a
lens that gives a narrower field of view than a standard lens".


"That doesn't sound very wrong. In fact, not at all."

What about wide angle telephoto lenses, which were/are very widely
used on compact fixed-focal length film cameras? Most of these
lenses had a focal length of about 35mm with a vertex length slightly
less than that. IMO, any lens with a vertex length shorter than its
focal length is rightfully called a telephoto lens, regardless of the
field of view. Interestingly, some of the long EFL fast telephoto
lenses have a vertex length slightly longer than their focal length.
For example, the 200mm f/2 Nikkor is 245mm long, and the 300mm f/2
Nikkor is 359mm long.

All of these are good points, and raise the question of whether lenses
should be described by their function, rather than such technical
qualities that may or may not be perceivable by the purchaser/user? If I
want to buy a "telephoto lens", the *last* thing I want someone to hand me
is a lens with a 35 mm's field of view! ;-)

Neil

BC writes: What about wide angle telephoto lenses, which were/are
very widely used
on compact fixed-focal length film cameras? Most of these lenses had a

focal length of about 35mm with a vertex length slightly less than
that.

You are correct in meeting the definition that 'telephoto' is a lens
whose front element is closer to the film than its focal length. The
'old time' definition of 'telephoto' was typically in the context of
lenses that also have the visual effect of bringing things in closer
than the 'normal' length (diagonal of film frame), and 'normal' vs.
'telephoto' became synonymous with 'magnifying' rather than the optical
definition (lens front to film plane) and the optical definition (image
nodal plane is in front of the lens) or lens construction definition
(positive element in front of a negative element, with air space in
betwee the two elements).
So really you're more correct in stating 'normal focal length of
telephoto design' (vs. what we typically mean by 'telephoto'...'long
focal length of telephoto design').

--Wilton

wilt wrote:

You are correct in meeting the definition that 'telephoto' is a lens
whose front element is closer to the film than its focal length. The
'old time' definition of 'telephoto' was typically in the context of
lenses that also have the visual effect of bringing things in closer
than the 'normal' length (diagonal of film frame), and 'normal' vs.
'telephoto' became synonymous with 'magnifying' rather than the optical
definition (lens front to film plane) and the optical definition (image
nodal plane is in front of the lens) or lens construction definition
(positive element in front of a negative element, with air space in
betwee the two elements).

But on the other hand... 'tele' is Greek for 'far'. I would guess that
originally the term 'telephoto' was coined to describe photographs taken
from far away. The definition used by lens designers became later.

IIRC, Leica made a 800mm lens that is a simple triplet, but nobody would
call it a 'normal' lens.

-- Lassi

"Lassi Hippeläinen" wrote in message
...

But on the other hand... 'tele' is Greek for 'far'. [...]

?????? ???!

"jjs" wrote in message
...
"Lassi Hippeläinen" wrote in message
...

But on the other hand... 'tele' is Greek for 'far'. [...]

?????? ???!

Crap. Greek characters don't show up. Shoulda done rich text.

BC wrote:

What about wide angle telephoto lenses, which were/are very widely used
on compact fixed-focal length film cameras?

The thing is that there is more than one corect usage, more correct
definitions of "telephoto".
A lens that has a narrower angle of view than the lens that is considered
"normal" for the format is one.
A lens of certain optical construction is another.

I suspect that the original definition is the one involving the
telephoto ratio that optics people have always used, and the other
definition grew up around a popular misunderstanding of the term. I
recognize that usage rules, but reserve the right to complain about it!

Brian
www.caldwellphotographic.com