When you change the focal length of your lens
either by zooming in and out or perhaps by
putting on a short wide angled lens
not only are you changing the magnification that's what makes far off things come
closer
you're changing three other things as well.
You're gonna have an impact on perspective,
depth of field and
field of view, field of view is like how much you can get into the picture.
To explain this Jane and i have spared no expense in building our
specially painted
field of view demonstrating engine.
All of this is the made using the finest quality garden shed materials, let me just put these
lenses down here,
so i can say what i mean.
Now you imagine
this silver painted drain rods
beautiful that they are
are the barrel of the lens, this is kind of what you're gonna see through your
lens,
and this bit here, the bicycle wheel is the glass at the end. If i have a
wide-angle lens
a short focal length
that's this distance here is short.
I've got a very wide field of view, as i look along these rods what i can see
pans out all the way across over there, to the side all the
way out to the hills over there,
it's a very wide field of view.
If i'd zoomed the lens by increasing this bit,
the focal length,
what happens is
it draws in the field of view, you see how these rods are getting closer
and narrower,
because of this i think we should call long lenses
'narra lenses'
but we don't unfortunately, we're stuck with what we've got.
How does it impact real life?
let's go and have a look at this through a camera.
Beginning with a wide-angle lens and a wide field of view
we're gonna use this rock here, this stone
is the anchor point for this little film.
Now as you can see except
roughly on the
left hand side third
filling the frame,
over this side of the picture you've got
those bushes along the side of the road there,
over here on the other side
you can't you see there's a little standing stone over there
and then the brown field beyond going all the way to the horizon.
If you wanted to get the same shot of this stone
but without all that going on either side
you'd need to narrow the field of view and you'd do that by using a longer lens.
With a long lens the first thing you'd probably notice is there seems to be
more stones in this shot,
that's a perspective thing we're gonna talk about that in a minute just ignore
it.
Think about the field of view,
this business
remember the bushes
over on that side of the road
they've all gone now haven't they
and the edge of the picture on this side
are the bushes way on the top of the hill there.
Similarly on the other side of the stone
the brownfield where the frame did end
that's now disappeared hasn't it, we've excluded that and it's
edging on the greenfield down the other side of the stone here.
Yeah our friend the stone
is the same size in this shot as it was in the wide angle shot, it's occupying
the same space in the frame.
Now because of the magnification aspect Jayne's had to move back with the camera
in order for it to fit
but it's in the same place
and we've excluded stuff down either side.
The other characteristic of the wide lens is perspective,
it stretches things out, it moves them further apart
so something that's close to the
lens will seem quite large and will pull towards it, stuff that's further away will seem tiny.
See these rocks up behind here, they look really tiny and like
they're a huge distance away, they're not let's pace it out, look, one, two, three, four, five, six, seven
eight, nine, ten,
eleven, twelve, thirteen, fourteen
fifteen, sixteen, seventeen, eighteen, nineteen, twenty
twenty-one places that's all it is from where you are
to this rock here.
but it looks really really tiny
like it's off into the distance,
that's because the short lens that expands perspective.
let's take a quick look at it
with a longer lens, it's the same shot, keeping this stone the same size in the
picture. Now we mention there seem to be a lot more stones in the shot, there are no more
stones in this shot to a moment ago,
what has happened is the magnification part has compressed perspective,
long lenses
flattened things together they draw stuff that's a long way away and they
bring it forward
and they kind of stack them, bom ,bom, bom, bom, bom like that, one behind the other
and that's what's going on at the moment.
The rock
behind this one, the stone behind this one is till only twenty one paces away
from where i am,
it hasn't changed at all despite the fact it looks considerably closer,
that's about perspective stacking that's how you get those shots of mountain
ranges going off into the distance and coming together and we've done it with
a bunch of standing stones.
Short lenses, that's wide lenses
with all the wide field of view
they also have a massive depth of field,
depth of field
is how deep
the focus of your shot is,
how much you've got sharp
from in front of the camera to off into the distance.
Now just now when i walked back over there to where that cow is now playing
around with our rock
i was sharp all the way wasn't i? from here back to there
and as i come towards you now
i'm still sharp up to about here
that means the death of focus
with a short wide lens stretches from what three, four feet in front of the
camera
in this case Janes video
all the way to the horizon, that is an immense amount of depth of field.
The final part of this puzzle
is the long lens
and depth of focus, now depth of focus, depth of field it's the same thing
now as i'm walking towards you
i'm slowly shifting myself
out of focus.
The camera is focused on the stone i was standing next to,
and as i'm coming forward
i'm getting myself more and more soft in your view finder.
In a moment to when i got about five or six feet in front of the camera
i'll be very soft indeed
i reckon i look positively drunk by now.
Now then if Jayne just re-focuses the camera on me
so that i come sharp
there we go that's better isn't it.
I'm nice and sharp,
but look any stones that are behind me
look, they've gone completely soft.
If i move towards the camera
if you remember with a short lens, i could come all the way up to three feet
and and i was still nice and sharp, look if i start walking towards you now
i reckon i'm out of focus here.
This is an inherent thing with a long lens it has a shallow depth of field
very shallow depth of field if i was to walk back up this way
the same sort of thing would happen as i'm going backwards
i'm getting softer in the shot as well
just like when i went forward.
It's more pronounced when i come close to the camera
so if you start doing close-up work with the long lens and it's a great tool for close
up work
you've got to be very very careful with your focusing
because your depth of field
is very very shallow
with a long lens.