Canon 350d wide angle converter

Gormless wrote:


"Randall Ainsworth" wrote in message
...

Well...20mm x 1.6 = 44.8mm.

As my old father used to say: 2 x 2 = 5 (for very large values of 2)

Pi = 3 for large values of 3 and small values of Pi.

writes:

I had always taken 'normal' to be approximating to the human eye, not to
what is conventionally fitted as 'standard' on a particular kind of
camera.

But what does "the human eye" have as a field of view? The eye has a
high-resolution field of view of only a few degrees - but we can see
much more without moving our heads by scanning the eyes serially over
whatever parts of the scene look interesting. The scannable field is
wider than most wideangle lenses can capture.

Plus there's the low-resolution but motion-sensing peripheral vision,
which can see 180 degrees horizontally at one time. No way to match
that without a fisheye.

So what is normal?

Dave

On Wed, 24 Aug 2005 02:08:06 +0000 (UTC), (Dave
Martindale) wrote:

writes:

I had always taken 'normal' to be approximating to the human eye, not to
what is conventionally fitted as 'standard' on a particular kind of
camera.

But what does "the human eye" have as a field of view? The eye has a
high-resolution field of view of only a few degrees - but we can see
much more without moving our heads by scanning the eyes serially over
whatever parts of the scene look interesting. The scannable field is
wider than most wideangle lenses can capture.

Plus there's the low-resolution but motion-sensing peripheral vision,
which can see 180 degrees horizontally at one time. No way to match
that without a fisheye.

So what is normal?

Dave

Google is your friend! :-)
One of many hits:
http://www.digicamhelp.com/what-is-a-normal-lens/
For 35mm, this site says 50mm.
When I took up photography mumble years ago, I was told by many it
was anywhere from 45mm - 55mm; the variance is because we don't all
see the same. But I see the photography world has pretty much settled
on 50mm. Maybe partly because 50mm is a very popular lens focal
length, as well as being in the center of that range.

--
Bill Funk
Replace "g" with "a"
funktionality.blogspot.com

In article , Bill Funk
writes
Maybe partly because 50mm is a very popular lens focal length,

So, it is popular because it is popular?

as well as being in the center of that range.

This seems a more logical explanation.
--
Ian G8ILZ

Bill Funk writes:

Google is your friend! :-)
One of many hits:
http://www.digicamhelp.com/what-is-a-normal-lens/
For 35mm, this site says 50mm.

You're talking about the normal photographic meaning of "normal".
There, a normal lens is one that gives an image with natural perspective,
given some assumptions about the size of print and viewing distance.

But this "normal" lens has a focal length somewhere near the diagonal
of the image, and a horizontal field of view of something near 40-50
degrees. That's nothing like the human eye, which is what the previous
poster said defined normal for him. I was asking what *that* use of
normal means in a lens.

Dave

In article , Dave Martindale
writes
writes:

I had always taken 'normal' to be approximating to the human eye, not to
what is conventionally fitted as 'standard' on a particular kind of
camera.

But what does "the human eye" have as a field of view? The eye has a
high-resolution field of view of only a few degrees - but we can see
much more without moving our heads by scanning the eyes serially over
whatever parts of the scene look interesting. The scannable field is
wider than most wideangle lenses can capture.

Plus there's the low-resolution but motion-sensing peripheral vision,
which can see 180 degrees horizontally at one time. No way to match
that without a fisheye.

So what is normal?

A normal lens is one which has a focal length equivalent to the diagonal
of the film (not withstanding the possible use with smaller sensors).
The angle of view (53 deg.) with such a lens is approximately equal to
the angle over which an inattentive eye can roam, without moving the
head.

For correct perspective an enlargement should be viewed at a distance
equal to the focal length multiplied by the degree of enlargement.

If we were to reproduce what the eye/brain perceives (N.B. not what the
eye sees) then we would indeed have to use a 180 deg fish eye and make
an infinitely large print. If we wished to replicate the human eye we
would need a video camera with a narrow angle of view which could be
swept around the scene and software to assemble a larger picture, and
this is only a first approximation

Here endith the first lesson. I have been taking photographs for (quite)
a few years now, if you need a few pointers try a library; if anything
is still unclear ask here.
--
Ian G8ILZ

On Wed, 24 Aug 2005 08:57:13 +0100, Prometheus
wrote:

In article , Bill Funk
writes
Maybe partly because 50mm is a very popular lens focal length,

So, it is popular because it is popular?

That's not what I meant.
It (50mm rather than, say, 48mm) is chosen as "the" normal focal
length because that length is a popular length, and there aren't very
many 48mm lenses.


as well as being in the center of that range.

This seems a more logical explanation.

I agree. Maybe I should have reversed the order. :-)

--
Bill Funk
Replace "g" with "a"
funktionality.blogspot.com

On Wed, 24 Aug 2005 08:22:04 +0000 (UTC), (Dave
Martindale) wrote:

Bill Funk writes:

Google is your friend! :-)
One of many hits:
http://www.digicamhelp.com/what-is-a-normal-lens/
For 35mm, this site says 50mm.

You're talking about the normal photographic meaning of "normal".
There, a normal lens is one that gives an image with natural perspective,
given some assumptions about the size of print and viewing distance.

But this "normal" lens has a focal length somewhere near the diagonal
of the image, and a horizontal field of view of something near 40-50
degrees. That's nothing like the human eye, which is what the previous
poster said defined normal for him. I was asking what *that* use of
normal means in a lens.

Dave

I dunno.
Here's your post I responded to:

"But what does "the human eye" have as a field of view? The eye has a
high-resolution field of view of only a few degrees - but we can see
much more without moving our heads by scanning the eyes serially over
whatever parts of the scene look interesting. The scannable field is
wider than most wideangle lenses can capture.

Plus there's the low-resolution but motion-sensing peripheral vision,
which can see 180 degrees horizontally at one time. No way to match
that without a fisheye.

So what is normal?"

What lens are you referring to when you ask what's normal?
If you are trying to ask about a lens that includes the periferal
vision, which I think you are now, I have to say, again, 50mm, because
that lens fits the media (35mm) and provides the same approximate
perspective (within that media) that the human eye does. If you want
the same *coverage*, you need to either change the media, or accept
cropping along the top and bottom of the media ("Letterbox" photos?
:-) ).
--
Bill Funk
Replace "g" with "a"
funktionality.blogspot.com

In article ,
says...
What lens are you referring to when you ask what's normal?
If you are trying to ask about a lens that includes the periferal
vision, which I think you are now, I have to say, again, 50mm, because
that lens fits the media (35mm) and provides the same approximate
perspective (within that media) that the human eye does. If you want
the same *coverage*, you need to either change the media, or accept
cropping along the top and bottom of the media ("Letterbox" photos?
:-) ).

The perspective has nothing to do with whether you are using different
lenses or the human eye. Perspective is determined by your distance
from the subject, and nothing else.