"telephoto" - another definition problem

I decided I might like a "true" very-high-quality 1:1 macro lens for
the EOS mount so I did a search on "process lens" (due to a discussion
in another thread that suggested a 1:1 top quality symettrical "macro"
lens is called a "process lens") and did not find any EOS Canon lenses
to match. That's not saying there is no such thing - but I didn't find
any. I am guessing they will be called "macro" lenses and I wonder if I
could tell if it were optimised for 1:1. But never mind, the word
"macro" means different things to different people and it seems like
the camera manufacturers prefer to keep people confused as to the
definition. But that aside, I walked two doors down the corridor to ask
a fellow photography enthusiast what his definition of "telephoto" was.
It was different to mine.

So what is the definition of "telephoto"?

And once we are all sure of what it is, then what is the definition of
"reverse telephoto" and "telephoto ratio" and does this fit with the
definition of "telephoto"?

RolandRB kirjoitti:
...
So what is the definition of "telephoto"?

From engineering point of view, a telefocus lens is physically shorter
than its focal length. In practise it means that the lens has a negative
group behind a positive group (think about the lens equation, 1/f = 1/f1
- 1/f2). A lens that doesn't use the trick is called a straight focus lens.

And once we are all sure of what it is, then what is the definition of
"reverse telephoto" and "telephoto ratio" and does this fit with the
definition of "telephoto"?

Reverse telefocus must mean retrofocus, i.e. a lens that is physically
longer than its focal length. Sort of tele in reverse: a positive group
behind a negative group. The structure is used in SLR wide angles that
must have room for the mirror between the rear element and the film.

-- Lassi

RolandRB kirjoitti:
...
So what is the definition of "telephoto"?

From engineering point of view, a telefocus lens is physically shorter
than its focal length. In practise it means that the lens has a negative
group behind a positive group (think about the lens equation, 1/f = 1/f1
- 1/f2). A lens that doesn't use the trick is called a straight focus lens.

And once we are all sure of what it is, then what is the definition of
"reverse telephoto" and "telephoto ratio" and does this fit with the
definition of "telephoto"?

Reverse telefocus must mean retrofocus, i.e. a lens that is physically
longer than its focal length. Sort of tele in reverse: a positive group
behind a negative group. The structure is used in SLR wide angles that
must have room for the mirror between the rear element and the film.

-- Lassi

Lassi Hippel=E4inen wrote:
RolandRB kirjoitti:
...
So what is the definition of "telephoto"?

From engineering point of view, a telefocus lens is physically
shorter
than its focal length. In practise it means that the lens has a
negative
group behind a positive group (think about the lens equation, 1/f =3D
1/f1
- 1/f2). A lens that doesn't use the trick is called a straight focus
lens.

And once we are all sure of what it is, then what is the definition
of
"reverse telephoto" and "telephoto ratio" and does this fit with
the
definition of "telephoto"?

Reverse telefocus must mean retrofocus, i.e. a lens that is
physically
longer than its focal length. Sort of tele in reverse: a positive
group
behind a negative group. The structure is used in SLR wide angles
that
must have room for the mirror between the rear element and the film.

-- Lassi

That matches exactly with the definitions I assume. We are in a 100%
majority!!

RolandRB wrote:
Lassi Hippel=E4inen wrote:
RolandRB kirjoitti:
...
So what is the definition of "telephoto"?

From engineering point of view, a telefocus lens is physically
shorter
than its focal length. In practise it means that the lens has a
negative
group behind a positive group (think about the lens equation, 1/f =3D
1/f1
- 1/f2). A lens that doesn't use the trick is called a straight
focus
lens.

And once we are all sure of what it is, then what is the
definition
of
"reverse telephoto" and "telephoto ratio" and does this fit with
the
definition of "telephoto"?

Reverse telefocus must mean retrofocus, i.e. a lens that is
physically
longer than its focal length. Sort of tele in reverse: a positive
group
behind a negative group. The structure is used in SLR wide angles
that
must have room for the mirror between the rear element and the
film.

-- Lassi

That matches exactly with the definitions I assume. We are in a 100%
majority!!

Um, I don't have any of my texts ready to hand to quote from, but I
think you're both mistaken. Telephoto lenses have a positive
(converging) group at the front and a negative (diverging) group at the
rear. Their principal planes are reversed, i.e., rear principal plane
is farther from the film than the front principal plane. As a result,
a telephoto lens requires less extension to focus to infinity (or
anywhere closer) than a non-tele lens.

You guys seem to be thinking of lenses in focusing mounts, in which
case a tele lens, mount included, will be shorter than a conventional
lens of the same focal length. But there are lenses that aren't in
focusing mounts, e.g., short mount lenses for SLRs and lenses for view
cameras. For them, the definition you like makes no sense at all. I
fear you're both working at too low a level of abstraction.

Roland, get a couple of good books and study them. Lassi, do the same.

RolandRB wrote:
Lassi Hippel=E4inen wrote:
RolandRB kirjoitti:
...
So what is the definition of "telephoto"?

From engineering point of view, a telefocus lens is physically
shorter
than its focal length. In practise it means that the lens has a
negative
group behind a positive group (think about the lens equation, 1/f =3D
1/f1
- 1/f2). A lens that doesn't use the trick is called a straight
focus
lens.

And once we are all sure of what it is, then what is the
definition
of
"reverse telephoto" and "telephoto ratio" and does this fit with
the
definition of "telephoto"?

Reverse telefocus must mean retrofocus, i.e. a lens that is
physically
longer than its focal length. Sort of tele in reverse: a positive
group
behind a negative group. The structure is used in SLR wide angles
that
must have room for the mirror between the rear element and the
film.

-- Lassi

That matches exactly with the definitions I assume. We are in a 100%
majority!!

Um, I don't have any of my texts ready to hand to quote from, but I
think you're both mistaken. Telephoto lenses have a positive
(converging) group at the front and a negative (diverging) group at the
rear. Their principal planes are reversed, i.e., rear principal plane
is farther from the film than the front principal plane. As a result,
a telephoto lens requires less extension to focus to infinity (or
anywhere closer) than a non-tele lens.

You guys seem to be thinking of lenses in focusing mounts, in which
case a tele lens, mount included, will be shorter than a conventional
lens of the same focal length. But there are lenses that aren't in
focusing mounts, e.g., short mount lenses for SLRs and lenses for view
cameras. For them, the definition you like makes no sense at all. I
fear you're both working at too low a level of abstraction.

Roland, get a couple of good books and study them. Lassi, do the same.

RolandRB wrote:

That matches exactly with the definitions I assume. We are in a 100%
majority!!

So you and your fellow photography enthusiast two doors down the corridor
did not disagree after all?
;-)

Dan Fromm kirjoitti:
... I fear you're both working at too low a level of abstraction.

I did it on purpose. Talk to the customer in the customer's language...

BTW, my shortest telefocus lens is the 35mm/2.8 on my Olympus XA
rangefinder. A wide-angle tele ;-)

-- Lassi

Q.G. de Bakker wrote:
RolandRB wrote:

That matches exactly with the definitions I assume. We are in a
100%
majority!!

So you and your fellow photography enthusiast two doors down the
corridor
did not disagree after all?
;-)

We did disagree but he has not cast his vote here.

Q.G. de Bakker wrote:
RolandRB wrote:

That matches exactly with the definitions I assume. We are in a
100%
majority!!

So you and your fellow photography enthusiast two doors down the
corridor
did not disagree after all?
;-)

We did disagree but he has not cast his vote here.