I’m appalled at the number of newbie “professionals” I see talking on the photo-forums about buying and using the 85mm f1.2 (or 1. anything) lens wide open for portraits. Using your lenses widest aperture (f2.8 or otherwise) is unwise in most circumstances especially when doing portraits of paying clients! I expect amateur photographers’ cavalier attitude of wide open apertures just due to their general lack of technical knowledge, but so called professionals must be aware and educated about what their tools can and cannot do. As professionals we must deliver exceptional quality in our images on every session we do—no excuses!
Even when I’m doing fine art photography, just for myself, I’m very careful about depth-of-field and mindful of all the variables that affect it. One of the most important variables that has a huge effect on the depth-of-field, that your selected aperture will yield, is the distance between your camera and the subject.
To illustrate this effect the following images were exposed at the same aperture (f8.0), but at different distances….
 |
|
f8.0 @ 1/250 sec., ISO 800; Distance: 24:; Lens @ 84mm
|
Even at f8.0 you can see that the depth-of-field is very shallow when in this close. By using f8.0 I got nice sharp blossoms on just he nearest vine while everything else went nicely out of focus.
Using DoFMaster.com’s depth-of-field calculator ~
With my DLSR’s sensor: APS-C Nikon
- at f 8.0
- lens@ 84mm
- at 24” from subject
- the DOF is .56” (just over 1/2 inch) Just what I wanted!
If I had gone wide open:
- to f2.8
- the DOF would be .2” (only 2/10th of an inch)
So, let’s try really wide:
- to f1.2
- the DOF would be .08” (only 8/100ths of an inch!)
Virtually nothing would have been in focus with that little depth-of-field.
 |
|
f8.0 @ 1180sec., Iso 800; Distance 8 ft.;Lens @ 44mm
|
So, at this distance (8 feet) my aperture of f8.0 gives me a depth-of-field of 38.2” which was plenty to keep the vines in front of the tree trunk and the tree trunk sharp. Note: This works the same when photographing groups.
Other reasons not to “shoot” wide open:
- Most lenses are not very sharp wide open; they’re often sharper stopped down a couple stops.
- Many Lenses Vignette wide open creating dark corners around the image.
- Some lenses induce chromatic aberrations when wide open…(look it up).
So, in summation, we as professionals must know how to get the most from our tools in order to create the best product possible for our clients on every session. That’s why I don’t “shoot” wide open.
’Til next week…
Author: Jerry W. Venz, PPA Master Photographer, Craftsman
Training Site: http://www.LightAtTheEdge.com
Client Site: http://www.TheStorytellersUsa.com
What is Chromatic Aberration?
Chromatic aberration, also known as “color fringing” or “purple fringing”, is a common optical problem that occurs when a lens is either unable to bring all wavelengths of color to the same focal plane, and/or when wavelengths of color are focused at different positions in the focal plane. Chromatic aberration is caused by lens dispersion, with different colors of light traveling at different speeds while passing through a lens. As a result, the image can look blurred or noticeable colored edges (red, green, blue, yellow, purple, magenta) can appear around objects, especially in high-contrast situations.
