Re: Nikon D40 with 300mm lens AND teleconverter (Nikkor AF-S Teleconverter TC-20E II)

Neil Harrington wrote:
Wilba wrote:
Neil Harrington wrote:
Wilba wrote:
Neil Harrington wrote:

Greg obviously does have *some* idea about focal lengths, so
explaining the common 35mm equivalencies does not seem like
a bad idea. He's going to run into the concept sooner or later
anyway.

He does, it is, and he will, but he won't understand it from David's
explanation. :-)

I think he's better off understanding the perspective of a stated focal
length on his camera, like 100/33 = 3x, rather than 100*1.5/50 = 3x.

Not really. The "3x" in your examples tells him nothing useful.

If we accept that statement at face value, it's equally true to say that
"100mm tells him nothing useful".

Sure it does, if he's familiar with the effects of different focal lengths
and can visualize them with respect to the subject. If he's not, he
eventually will be. Presumably he already knows that magnification is
proportional to focal length, so "3x" tells him nothing new or useful.

Nice try, but let's get back to the point. (You do get it that the maths
above is only to illustrate the unnecessary complexity of thinking in focal
lengths for a format you're not using?)

For Greg, in using a camera like the D40, I believe he's better off thinking
of the view through an attached 100mm lens as a 100mm view, not a 150mm
view. You seem to disagree with me (but you do agree below). Neither of us
is entirely right or wrong.

What exactly do you expect him to do with the "3x"?

The same as you expect him to do with "100mm". The difference is,
with a magnification he may be able to relate it to other experience,
like looking through telescopes, binocculars, magnifiers, etc.

As I've pointed out, you are completely mistaken in trying to make that
sort of comparison. Your "3x" or any other "x" in connection with a camera
lens WILL NOT give him the same result as that power in a telescope or
binoculars.

You are completely mistaken in assuming that I did say or imply that it
would give him "the same result". And as you know, my point is not about 3x
or 50mm, but about 1.5.

Are you telling me that when you think "18mm on a 1.5 factor camera", you
are thinking predominantly of an actual angle? As a number of degrees?

Angles are measured in degrees, not millimeters.

I can't believe that anyone is genuinely stupid enough to think that "18mm
on a 1.5 factor camera" is an attempt to specify an angle! But just in case
you are, I was implying, "18mm LENS on a 1.5 factor camera". Blimey! :-)

... generally speaking with short lenses one naturally thinks in terms
of field of view, while with long lenses one thinks of magnification.

Ah! That's a new and different statement from you.

So here's Greg talking about shooting birds at 510mm ... dya reckon it might
be handy for him to think about magnification? Maybe? :-)

How do you think about magnification with long lenses?

People have used the argument to explain why 100mm (or thereabouts) is the
ideal f.l. for portraiture (on a 35), and I can't count the number of
times I've seen someone claim that it's "most natural" because it
duplicates the magnification of the human eye, i.e. that the image in the
viewfinder looks the same size as when seen with the naked eye. It simply
isn't true, or at least it's never been true on any SLR I've tried the
comparison with.

Aha. So you're talking about lenses for portraiture. You're right, it's
complete bull***, and nothing at all to do with what I'm talking about.
I've never heard anyone argue that a 100mm lens on a 35mm camera is a good
portrait lens because it duplicates the magnification of the eye. That
sounds like someone who doesn't know what they're talking about talking out
their arse.

"Normal" is almost meaningless. For head-and-shoulders portraiture a 100mm
lens does provide a natural look and a 50mm would be regarded by most
people as too short. For scenery, landscapes etc. a 50 is often too long.
It's also too long by the traditional rule which says normal focal length
should be about equal to the diagonal of the negative. People got used to
the idea of 50mm being "normal" simply because most camera makers accepted
the Leica standard f.l. as their own. But there have been rangefinder 35s
with (non-interchangeable) shorter lenses for almost as long as 35s have
been popular. In the early 1950s the popular Kodak Signet had a 44mm lens.
The Bolsey I think was about the same. Most of the Japanese RF 35s that
began to flood the country had 45mm lenses. The trend since then has been
for fixed focal length lenses on compact 35s to become shorter and
shorter, various models being 42, 40 and 38mm. The last compact 35s I
owned (Konica Big Mini, Yashica T4 and Olympus Stylus Epic) all had 35mm
lenses. All of those were "normal."

Except in the sense that I learnt it, and have been discussing.

Actually even with 35mm SLRs, I always preferred the 35mm lens to the 50mm
as a "normal." To me it always seemed the 50 was too long for some things
and too short for almost everything else.

Completely different and incompatible idea of normal. To me, an abnormal
idea of normal. :-D

My experience, having done the experiment as described, is that 50mm
gives a "normal" view, as described in the literature I read when I got
that camera.

Try it again. This is very hard to do accurately. You have to have both
eyes open of course, and the viewfinder image is somewhat displaced
vertically as well as horizontally. Use a zoom lens and change the focal
length while turning the camera slightly from side to side. See which way
a distant image moves relative to what's outside the viewfinder. If it
moves in the same direction you're turning the camera, the f.l. is too
short; if it moves in the opposite direction the f.l. is too long. When it
doesn't move at all you're at unity magnification, i.e. the same
magnification as the naked eye. Do this very carefully; the object is to
find the point at which there is absolutely no movement one way or the
other. With my Minolta 700si it's just a little short of 70mm on the zoom
ring. With my Nikon D80 it's a little above 45mm.

Interesting way to do it. Thanks for that. I found the best way was to hold
the camera vertical so that I had an unobstructed view with the other eye.
Using a 28-70mm on my ME Super, it's a smidge past the 50mm mark.

Again, this really doesn't show anything about what's "normal." It will
vary with the magnification of the camera's viewfinder system.

Yes, you need a viewfinder with a magnification near 1. Which way would it
go - if your experiment gives a result of Xmm, would you multiply by the
magnification of the viewfinder, or divide?

On a 35mm SLR, the f.l. with apparent unity magnification is usually
around
70mm, ...

Not with the ME Super here on my desk.

Have you actually tried it at about 70mm?

Yes, 28-70mm. If I had to put a number to it, I'd say 55mm.

You seem to be arguing that Greg is better off to learn to think of his
view through an 18mm lens on a D40 as a "28mm" view, rather than
as an "18mm" view.

Not necessarily, but the concept of 35mm lens equivalence is now well
established and everyone uses it, not just for DSLRs but for all kinds of
digital cameras. In fact it actually started with APS cameras, which were
considered to have a lens factor of 1.25x.

However, the equivalencies obviously are more useful to those of us who
are familiar with focal lengths associated with 35mm cameras. If Greg is
not, I don't think there's any particular reason for him to become
concerned with them, but he will surely be seeing them mentioned often in
the literature and might as well have some understanding of what they're
about.

Well that's what I've been saying all along, so there's nothing left to
argue about. :-)

I'm not sure that's the best advice. Other than compliance with
convention, why is it?

Just the fact that it *is* a convention makes it worth adhering to. You
could measure distance in stadii or room size in cubits, but few people
would grasp what you were saying since those units are not the
conventional ones nowadays.

Unless those were the units engraved on your lens ... then I'd say you're
better off working in those units, and converting them for discussion.


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