1 The Director of Photography – an overview

54 Practical Cinematography
Figure 5.4 The effect of using
different apertures
Max Aperture
T1.3
Max Aperture
T2
Shooting
Aperture
T3.2
on some scenes, though perhaps not on others. You have decided this
because you want to vary the definition between scenes as part of your
overall strategy for the visual pacing of the film. You will achieve the
variation by the use of filters of different strengths.
You might, say, look to Zeiss Super Speeds as your prime lens set.
They are truly magnificent lenses. But, if you are never going to open
them up beyond T3.2, is this wise? Remember you want maximum
definition in some scenes in order to contrast this with others.
Let us compare a T1.3 lens and a T2 lens both working at an aperture
of T3.2. For simplicity, Figure 5.4 shows a single component lens,
but imagine what happens in a compound retrofocal lens containing
many elements – things are much worse.
As you can see, when both lenses are working at an aperture of T3.2
the light has to go through far more glass in the T1.3 lens than in the T2
lens. Now it should be obvious that the more glass the light has to go
through, at any given aperture, the more aberrations are likely to occur.
So, why expect a T1.3 lens to give a finer picture at T3.2 than a lens
with a maximum aperture of T2? There are strong arguments to say
that it won’t.
A further disadvantage is that many lenses with maximum apertures
of around T1.3 have minimum apertures of only T11, and at T11
they often perform far from their best – imagine how much glass there
must be right in the centre of such a lens.A lens with a maximum aperture
of T2, on the other hand, will usually stop down to T16 or even
T22 – quite an advantage with today’s high-speed films.
Telephoto lenses
With telephoto lenses all the above remains true, but you have to take
depth of field into account in choosing which lens to use.There is little
point in trying to do a tricky focus pull on, say, a 300 mm lens at T2.8 if
there is any way you can light up to T4 or better. If the shot is going to
be a nightmare at T2.8, you might be better to swap to a higher speed
film just for that one shot – the extra grain hardly ever shows when it
is cut together. So, if you are going to try and avoid shooting at T2.8
with your 300 mm, why order such a fast lens? A 300 mm T4 lens might
very well perform better at T4 than the T2.8 lens stopped down to T4
or it might not, you would need to run a test.
A telephoto lens is not the same as a prime long-focus lens.Telephoto
means the lens has been optically telescoped and is therefore physically