32
H4D
True Focus
True Focus is primarily intended to relieve a situation caused by wanting to use auto-
focus while having to continually make compositional changes. To be able to exploit
True Focus correctly, a few important points should be studied in order to obtain a full
understanding of how and when to use it.
Basically, there are four variables to pay attention to and they are listed below. The closer
you remain to the ideal situation with regard to these variables, the more noticeable the
effect of True Focus will be.
The variables are:
1. Proximity of camera to subject
2. Focal length of lens
3. Aperture setting
4. Movement of camera and/or subject after setting.
Taking these points in order:
a. The closer you are to the subject, the worse the original problem becomes. Conse-
quently, the need for True Focus solution becomes greater and its application there-
by becomes more noticeable.
b. Short focal length ('wideangle') lenses naturally decrease camera to subject distanc-
es and therefore, following the point in (a), produce a greater need for True Focus
adjustments.
c. Smaller apertures increase the depth of field and therefore would lessen the need for
a True Focus solution. However, smaller apertures produce a different visual effect,
so True Focus therefore allows the exploitation of shallow depth of field without the
fear of unwanted focus restrictions.
d. The mechanics of True Focus use, amongst other things, camera to subject distances
to calculate the required amount of adjustment. It therefore follows that if the cam-
era or the subject move after the initial setting has been made, the calculations will
not be applicable anymore. So, to ensure the optimum correction, both the pho-
tographer and the subject should restrict movement as much as possible. Please
note that with some lenses (particularly longer length lenses) just a few centimeters
movement can essentially ruin the result.
The obvious situation that would most benefit from using True Focus would be a fashion
shoot with a fairly wideangle lens at a large aperture setting and where the central area
of the image is clothing while retaining focus on the model's face. Ideally, a fairly con-
trolled and static flow should be planned on (this means a change of pose by the model
should take place only after captures and the photographer must resist crouching down,
or leaning forwards or backwards too much before capture).
True Focus can be used with longer lenses, smaller apertures etc but the further you
come from situations similar to the 'ideal' as described above, the less the effect will
be until it has no visible effect at all. Please remember that although True Focus can
noticeably improve a demanding shoot it will only work effectively in the specific cir-
cumstances it was designed for.
Below you will find an illustration describing the principle behind True Focus and how it
works in practice.
