Telephoto Binocular Comparison

I am in the process of buying a new pair of binoculars and wondered if there
was any way to compare the focal length of a telephoto lens to the power
rating of binoculars. It would be nice to know how the scene I am looking
at thru the binoculars relates to my lens length.

An 8x40 pair of binoculars, have an lens diameter of 40mm and a
magnification of 8 times.
A telephoto lens of 400mm also has a 8 times magnification since 50mm is
defined as normal.


"foto" wrote in message
m...
I am in the process of buying a new pair of binoculars and wondered if
there
was any way to compare the focal length of a telephoto lens to the power
rating of binoculars. It would be nice to know how the scene I am looking
at thru the binoculars relates to my lens length.

If you think of a 50 mm lens as a standard 35 mm camera lens, then multiply
magnification factor of the binocular by 50 to get an approximate equivalent
35 mm camera lens. For example, if your binoculars are 8x40, the equivalent
35 mm lens would be 8 x 50 = 400 mm. (The 40 in the binocular designation
refers to the diameter of the front lens in millimetres.)

Scott Elliot
http://www3.telus.net/selliot/

"foto" wrote in message
m...
I am in the process of buying a new pair of binoculars and wondered if
there
was any way to compare the focal length of a telephoto lens to the power
rating of binoculars. It would be nice to know how the scene I am looking
at thru the binoculars relates to my lens length.

"foto" wrote in message om...
I am in the process of buying a new pair of binoculars and wondered if there
was any way to compare the focal length of a telephoto lens to the power
rating of binoculars. It would be nice to know how the scene I am looking
at thru the binoculars relates to my lens length.

This is not really possible, because binoculars have varying angles of
view quite independent of magnification. Lenses do not.

"Michael Scarpitti" wrote in message
om...
"foto" wrote in message
om...
It would be nice to know how the scene I am looking
at thru the binoculars relates to my lens length.

This is not really possible, because binoculars have varying angles of
view quite independent of magnification. Lenses do not.

Dividing the lens focal length by the focal length of a normal lens (assumed
to be 50mm for a 35mm camera) is a good way to approximate the
magnification.

The "varying angle argument" is equivalent to arguing if the 45 degree angle
of view of a 50mm lens is the same as what the eye sees. Sure it's an
approximation but otherwise you'll be forever debating whether a 40mm focal
length, a 50mm focal length, 55mm focal length etc is a normal lens.

The magnification of the camera's eyepiece affects the magnification of what
your eye sees when looking through the camera but not what the film sees.

-jeff

One can determine empirically what is "normal." Put a zoom lens (e.g.,
28-70) on a camera with a 100% viewfinder. Look through the viewfinder with
one eye (camera vertical) and compare the size of objects to what you see
with the other eye. Probably easiest on a tripod. To my eye, the size of
objects is equal in both eyes when the lens is around 60-70 mm. Could
someone confirm this? Isn't that what should really be called "normal".

--
- Alan Justice

"Jeff Keller" wrote in message
...

"Michael Scarpitti" wrote in message
om...
"foto" wrote in message
om...
It would be nice to know how the scene I am looking
at thru the binoculars relates to my lens length.

This is not really possible, because binoculars have varying angles of
view quite independent of magnification. Lenses do not.

Dividing the lens focal length by the focal length of a normal lens
(assumed
to be 50mm for a 35mm camera) is a good way to approximate the
magnification.

The "varying angle argument" is equivalent to arguing if the 45 degree
angle
of view of a 50mm lens is the same as what the eye sees. Sure it's an
approximation but otherwise you'll be forever debating whether a 40mm
focal
length, a 50mm focal length, 55mm focal length etc is a normal lens.

The magnification of the camera's eyepiece affects the magnification of
what
your eye sees when looking through the camera but not what the film sees.

-jeff

"Alan Justice" wrote

One can determine empirically what is "normal." Put a zoom lens (e.g.,
28-70) on a camera with a 100% viewfinder. Look through the viewfinder with
one eye (camera vertical) and compare the size of objects to what you see
with the other eye. Probably easiest on a tripod. To my eye, the size of
objects is equal in both eyes when the lens is around 60-70 mm. Could
someone confirm this? Isn't that what should really be called "normal".

Leica M3's worked this way -- the finder was very close to 1:1. But it
was 1:1 even with a 135mm mounted to the camera, it was just that the
camera put up an itty-bitty frame outline of the 135mm lens's view.

If you have a Speed Graphic the same thing happens with the wire frame finder:
it's always a 1:1 view, but with a longer lens the frame is farther from the
peephole and so delineates a smaller area of the scene.

In a 35mm SLR camera the angle of view the eye sees in the finder
is constant and is a function of the magnification of the focusing
screen image by the eyepiece lens. This is why the view looks distorted
for wide angle and telephoto lenses. If the view through a camera
looks 1:1 with a longish lens it is because the viewing magnification
is low and the viewscreen appears smallish. If the view into the
finder looks right with a wide-angle lens then the viewing magnification
is high and the view screen looks big.

Using 1:1 in the viewfinder as the criterion for a normal lens will
result in endless argument from a Nikon F user, who will assert
40mm is 'about right', and a Canon Rebel user, who will insist the
Nikon guy is all wet and the correct focal length is 70mm.

All in all the view through the finder has not a shaved farthing to
do with what constitutes a 'normal' lens.

In determining the 'normal' lens, the lens's focal length, the size
of the final print and the viewing distance of the print all have
to be in kopacetic harmony.

Try it: Select a 4x6" print of a shot made with a 20mm lens. Looks, er,
'wide anglish', right? Now look at it from 3 1/3" (yup, that's inches)
away (it helps to look through a large magnifying glass unless one is
terminally myopic) -- the resulting 'view' is now both natural looking and
wide angle at the same time. For viewing from a more comfortable distance
of 3'4" the negative should be blown up to 4x6 feet! The angle of view
of the scene in real life and the angle of view when looking at the
photograph should be the same; then, and only then, does the picture
look 'right'.

And that's why most photos look better when they are printed big, really
big, especially if taken with a wide angle lens. It is not that philistines
only care about the size of a photograph and not it's 'art'. Photographers insisting
on 6"x6" 'images' mounted on two foot square mat boards are screwing the
puppy for their viewers -- the reason most folks ignore these examples of
self-proclaimed 'fine art' isn't because they can't appreciate the artiste's
tremendous aesthetic sense -- it's because they can't properly see the
bleedin' 'image' in the first place, at least not without leaving nose-prints
on the picture glass.

A 50mm lens on a 35mm camera will produce a 4x6" print with the correct
perspective if the print is viewed from a distance of 8 1/3", and all
in all this is about right and 50mm is considered 'normal'. If the
picture is taken with a P&S with a 35mm lens the correct viewing
distance for a drugstore print is reduced to 6". And, if giving
P&S prints of the kids to granny, who threads a needle at arms
length, a 12x18" print would be appropriate.

There is another definition of what constitutes a 'normal' lens, but
it has little to do with taking pictures, it has to do with manufacturing
cost. If the lens focal length is about equal to the image circle
then a nice optimum is reached regards to design complexity,
manufacturing costs and lens performance. The best lens for the buck
is to be had when it's focal length is equal to the diagonal of the negative.
For 35mm the diagonal is 43mm, leading to the popularity of 45mm
lenses on rangefinder cameras of old where clearance for the mirror
is not an issue -- mirror clearance being the major factor extending
SLR lens focal lengths to 50mm. In the end it is not that 50mm or so
gives normal perspective, it is a matter of economics. Because of
this economic reason the standard print size is 4x6 (5x7" or 6x9"
is a better size for most folks, but again economics rules the day).

So, the correct "normal lens focal length" is really a function of the
size of the final photo and the distance from the photo to the viewer.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.

With your camera, the image is created on the focus screen. The camera's
eyepiece optics determine the image's apparent distance from your eye and
its size. The focus screen is probably about 6" away from your eye for most
35mm SLRs. Many people can not focus on something that close. The eyepiece
optics make it easier for your eye to focus on it. The eyepiece is
essentially providing a low power telescope view of the focus screen.

You've found that with your camera the combination of lens + eyepiece optics
gives a magnification of about 1X. If I do the same thing with my Olympus
OM4 I would say 50mm is very close to 1X when focused on something about six
feet away. For objects further away I probably also get about 60-70mm. Most
35mm SLRs have similar eyepiece optics.

The approximation that 50mm is a normal view comes from the fact that a
human has approximately a 47 degree angle of vision out of one eye held in
constant position. If a picture is taken using a normal lens, then printed,
if the picture is held at a distance that just fills the 47 degree angle of
vision, the view would be essentially the same as what your eye saw. If you
hold the picture closer so that only half of it fills your 47 degree angle
of vision, it would look like a 2x binocular view.

The other poster pointed out that some binoculars have a wider angle of view
for the same magnification. If you're buying binoculars this can be a big
improvement because your eye can slightly rotate to take in more of the view
without re-aiming the binoculars. However, the size of a bird viewed at a
fixed distance would be the same irrespective of the binocular's field of
view.

-jeff

"Alan Justice" wrote in message
ink.net...
One can determine empirically what is "normal." Put a zoom lens (e.g.,
28-70) on a camera with a 100% viewfinder. Look through the viewfinder
with
one eye (camera vertical) and compare the size of objects to what you see
with the other eye. Probably easiest on a tripod. To my eye, the size of
objects is equal in both eyes when the lens is around 60-70 mm. Could
someone confirm this? Isn't that what should really be called "normal".

--
- Alan Justice

"Jeff Keller" jeff-keller wrote in message
...

"Michael Scarpitti" mikescarpitti wrote in message
om...
"foto" wrote in message
om...
It would be nice to know how the scene I am looking
at thru the binoculars relates to my lens length.

This is not really possible, because binoculars have varying angles of
view quite independent of magnification. Lenses do not.

Dividing the lens focal length by the focal length of a normal lens
(assumed
to be 50mm for a 35mm camera) is a good way to approximate the
magnification.

The "varying angle argument" is equivalent to arguing if the 45 degree
angle
of view of a 50mm lens is the same as what the eye sees. Sure it's an
approximation but otherwise you'll be forever debating whether a 40mm
focal
length, a 50mm focal length, 55mm focal length etc is a normal lens.

The magnification of the camera's eyepiece affects the magnification of
what
your eye sees when looking through the camera but not what the film
sees.

-jeff

"Jeff Keller" wrote in message ...
"Michael Scarpitti" wrote in message
om...
"foto" wrote in message
om...
It would be nice to know how the scene I am looking
at thru the binoculars relates to my lens length.

This is not really possible, because binoculars have varying angles of
view quite independent of magnification. Lenses do not.

Dividing the lens focal length by the focal length of a normal lens (assumed
to be 50mm for a 35mm camera) is a good way to approximate the
magnification.

Camera lenses don't have 'magnification' at all. They cover certain
angles on certain sizes of film.

--
- Alan Justice

"Michael Scarpitti" wrote in message
om...
"Jeff Keller" wrote in message
...
"Michael Scarpitti" wrote in message
om...
"foto" wrote in message
om...
It would be nice to know how the scene I am looking
at thru the binoculars relates to my lens length.

This is not really possible, because binoculars have varying angles of
view quite independent of magnification. Lenses do not.

Dividing the lens focal length by the focal length of a normal lens
(assumed
to be 50mm for a 35mm camera) is a good way to approximate the
magnification.

Camera lenses don't have 'magnification' at all. They cover certain
angles on certain sizes of film.

It is magnification if you can see it better than with the naked eye, which
you can with a telephoto. Just like binoculars. My 600 gives about the
same magnification (to my eye, no film involved) as a 12x binocular.