Re: [OT] Lenses [Was: [OT] Cameras again]

In message <291220052205081470%nospam@xxxxxxxxx>
Elliott Roper <nospam@xxxxxxxxx> wrote:

> In article <98ea5e14d%Graeme@xxxxxxxxxxxxxxxxxxxx>, Graeme Wall
> <Graeme@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> > In message <291220051957312042%nospam@xxxxxxxxx>
> > Elliott Roper <nospam@xxxxxxxxx> wrote:
> >
> > > In article <4c2fffe04d%Graeme@xxxxxxxxxxxxxxxxxxxx>, Graeme Wall
> > > <Graeme@xxxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > >
> > > > At 35mm (50mm on a 35mm film camera) the perspective of the view is
> > > > very similar to the human eye. Shorter focal lengths expand the
> > > > perspective introducing increasing distortion until you eventually
> > > > get the fisheye effect. Longer focal lengths compress the
> > > > perspective.
> > >
> > > Just for the fun of arguing, and from a little bit of 'satiable
> > > curtiosity'[1], how can you tell?
> >
> > Very easy at the extremes.
> >
> > >
> > > Human eyes don't have a flat plane of film at a fixed distance from the
> > > optical centre of the lens. In fact they act like a view camera with a
> > > maniac in charge of the swings and tilts and lifts. Furthermore,
> > > depending on what you are looking at, they appear to switch off more or
> > > less of the retina (CCD) when it suits.
> >
> > Optically the human eyeball is crap, all the images have to be computer
> > processed before they are any use[1].
> OK, that's what I meant. The link between the optics and the human
> photoshopping is pretty close. If you enlarge a tiny fraction of an
> image taken with a 28mm lens, it will have the same perspective as the
> same image as a full frame telephoto subtending the same angle.

No it won't, think about it. You are dealing with a 2 dimensional image,
doesn't matter how much you enlarge the image the perspective is going to
remain the same, ie the ratio of size of foreground objects to background
objects will remain the same. Unless we are talking holograms and then all
bets are off.

> Does not your eye/brain system act a zoom lens in the same way?.

Nope, times when I wish it did

>
> > And if my failing memory[2] is still functioning, the retina is at a
> > fixed distance form the optical centre of the lens. It is this that
> > gives the eye a wider field of view than a camera lens of the same
> > effective focal length.
>
> Ah yes. Well spotted, although don't you mean 'depth of field'?

No, that is determined by the size of the iris, the larger the aperture the
smaller the depth of field. One advantage of prime lenses over zooms is that
you can have wider apertures than would be practical on a zoom lens, giving
you smaller depths of field, very useful on dramas to make the subject stand
out from the background.

> >
> > > Compare looking into the far distance to see if that is legs walking
> > > off the footpath as seen under a car parked 200m ahead, and catching
> > > sight in the side mirror of the glove of a biker about to do a loony
> > > mezzanine lane stunt behind you. In 35mm terms, that's a 18-500mm zoom
> > > in less than 0.2 sec.
> >
> > No it isn't, because the perspective hasn't changed, you've merely
> > altered the focus, you don't see the distant object any larger or the
> > near object any smaller.
>
> I strongly disagree with that. Your eye/brain is changing perspective in a
> very agile way between concentrating on fine detail in the far distance
> right in the middle of whatever bit of retina is best at that, and then on
> a close by blur exciting some other bit on the periphery just before the
> aforementioned bloke on the Yammy in the mezzanine lane almost clips your
> mirrors.

Nope. just altering focus. If you have a telephoto lens handy try framing a
picture with something close one side of the frame and a distant object the
other, pull focus from one to the other and you will get the same effect.
What I think is confusing you is the fact that the human eye is more
responsive to movement on the periphery of the visual field. A survival
characteristic.

>
> To sort-of answer my own question, but really to ask a deeper one, how
> about comparing photos of faces taken with various length lenses? At what
> focal length are the most flattering portraits taken? Would that be the
> natural "field of view" for looking at people?

Generally accepted that a slight compression of perspective makes for better
portraits, Peter C has pointed out that 85mm (on 35mm film) is regarded as
the ideal portrait lens. The least flattering is a wide angle lens at the
same framing, often seen on 'vox pops' on tv where the subject's nose is
exagerated compared with the ears.

> What about the same question with respect to scenery?

Difficult question to answer, depends on the scenery, too wide and you
flatten the view, probably a standard (ie 35mm on digital or 50mm on film) is
best, once again to match the perspective of the human eye.

> What role do swings and tilts play in architectural photography?

To eliminate the distortion inherent in not being able to photograph the
building from square on.

> Why does mucking about with the true perspective of vertical lines make the
> picture of a building look better?

Because if you don't the buildong appears to be falling backwards, blame it
on the photoshopper between your ears.

> What about the related question of the most natural aspect ratio for film
> or video?

That is a thorny question! 4:3, the conventional tv ratio, or academy ratio
for film, was adopted as a good compromise, it is broader than it is tall,
like the human eye but not such a wide field of view, thus concentrating the
attention on the framed subject better. Film went to widescreen framing to
better reproduce the field of view of the human eye and, alledgedly, to make
it difficult to show films on tv.

>
> I truly believe there are no easy to prove answers to any of this. You are
> a cine cameraman are you not?

<pedant> A tv cameraman, ie I work on tape not film. Not that that makes
much difference these days. My worst problem on film is changing the mags
and you get an assistance to do that for you.

> Is there a good reference book?

Any good book on photography should give you a good work out on the theory.

>
> Preferably one that does not try to snow me with golden means and
> stupid looking blokes with long arms standing in a circle.
>

Golden means are a whole different kettle of fish. Try the rule of thirds
for starters.

--
Graeme Wall

My genealogy website:
<http://www.greywall.demon.co.uk/genealogy/index.html>
.

Relevant Pages