Digital Depth of Field

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Digital Depth of Field
Presented by
N. David King
Digital Depth of Field
Depth of What???
 Before we talk about EXTENDING or
altering Depth of Field we need to make
sure we understand what it is and why we
might want to modify it.
 Depth of Field is the area from in front of
the main subject or plane of
critical/maximum sharpness to somewhere
behind the subject that APPEARS to be
focused in the final print or image.
© N. David King
Digital Depth of Field
Depth of What???
 Depth of Field is not real… it is an illusion
 This limited field of apparent sharpness, the “Depth of Field,” is
unique to photography and is used extensively to help isolate
subjects.
© N. David King
Digital Depth of Field
Depth of What???
 Depth of Field is not real… it is an illusion
 Our human vision links our optical input devices (eyes
and optic nerves) to our brains to constantly re-focus
as we scan a scene so it all appears to be sharp to us
from foreground to background.
 A camera lens cannot do that. There is only one point
in space where it is actually focused, i.e. rendering
points of light in the scene as the smallest circles of
confusion it can.
 That plane of sharpest focus, measured from the
cameras image plane, is called the “Focal Distance.”
© N. David King
Digital Depth of Field
Depth of What???
 Depth of Field is not real… it is an illusion
 As objects in space occur closer or farther away from
the focal distance, the lens produces larger circles of
confusion from each point of light.
 When those circles of confusion reach a size of
approximately 1/200 inch on a print, we will start to
see it as being “out of focus.”
 As objects increase in distance from the point of
sharpest focus they become increasingly out of focus
or “soft” and indistinct. It is painful for us to try to
focus something non-focusable so we look away.
© N. David King
Digital Depth of Field
Depth of What???
 Depth of Field is not real… it is an illusion
 This limited field of apparent sharpness, the “Depth of Field,” is
unique to photography and is used extensively to help isolate
subjects.
© N. David King
Digital Depth of Field
Depth of What???
 Depth of Field is not real… it is an illusion
 Depth of Field is actually a product of magnification but
photographers use several “controls” for it, most commonly the
aperture.
© N. David King
Digital Depth of Field
Depth of What???
 Depth of Field is not real… it is an illusion
 The result is extensive control over how much of the scene will
be in focus.
© N. David King
Digital Depth of Field
Depth of What???
 Depth of Field is not real… it is an illusion
 But there are times when we want a lot of Depth of Field in a
shot but stopping down the aperture is not a good method to
obtain it.
 Why? I’m glad you asked, otherwise I’d not have any excuse for
this presentation…
 Every lens has a “sweet Spot.” This is the spot where all of the
variables (aperture + focal distance + focal length for a zoom
lens) are optimized by the designers to achieve the greatest
possible sharpness.
 Opening up or stopping down from that point reduces sharpness.
 For the aperture part of the equation, with normal rectilinear
lenses that “sweet spot” is commonly (but not exclusively) at
about 2-3 stops closed down from wide open.
© N. David King
Digital Depth of Field
Depth of What???
 Depth of Field is not real… it is an illusion
 That means – unfortunately – that the sharpest aperture is not
anywhere near the aperture yielding maximum depth of field.
 For example for an f2.8 lens, the sweet spot is likely to be
somewhere around f5.6 to f8.
 (BTW…That means that the extra money spent for that fast lens
may be working against you for landscape and macro
shooting…)
 Before the digital world arrived on the scene, if you really wanted
or needed deep depth of field, all you could do was stop down
and live with it or in some cases solve it with the optical
movements on a large format view camera using the
“Scheimpflug Effect.”
© N. David King
Digital Depth of Field
Extending Depth of Field Digitally
 Thinking Digitally
 But working in the digital world we have some new options never
before available because of editing functions such as layering
and layer masks.
 This concept has existed almost from the first days of photo
editors using layers such as PhotoShop.
 The concept is really simple:
 Take enough shots so that in each shot you have something in
focus from front to back and in all of them you have everything in
focus due to overlapping depths of field from shot to shot.
© N. David King
Digital Depth of Field
Extending Depth of Field Digitally
 Thinking Digitally
 Here is what we are talking about.
© N. David King
Digital Depth of Field
Extending Depth of Field Digitally
 Doing It… The Shooting Part
 There are two main keys to success in shooting for
this outcome…
 PLANNING
 STEADINESS
 You must think this through before starting or it will
not come out as you wish.
 Your camera mount has to be so steady you can
adjust focus without moving the camera AT ALL.
© N. David King
Digital Depth of Field
Extending Depth of Field Digitally
 Doing It… The Shooting Part
 Here is an example using a common item you can all
relate to… a pair of push pins.
These pins were shot with
A 180mm f4 Macro lens set
At f11.
You can see that even at
f11 only the front tip of
the pin is sharp.
© N. David King
Digital Depth of Field
© N. David King
Digital Depth of Field
Extending Depth of Field Digitally
 Here is the assembled stack…
© N. David King
Digital Depth of Field
Extending Depth of Field Digitally
 So How is the Stack of Photos Assembled?
 Manually (for the true masochists out there…)
 With the Aid of Software
 Helicon (www.heliconsoft.com)
 PhotoShop CS4 and later
© N. David King
Digital Depth of Field
Extending Depth of Field Digitally

So How is the Stack of Photos Assembled?

The Process In PhotoShop
1.
2.
3.
4.
5.
6.
7.
8.
Open Bridge (File > Browse in Bridge)
In Bridge: Select all Shots
Tools > Photoshop > Load files into Photoshop Layers
In Photoshop: select all layers to make them all active
Edit > Auto Align
Edit > Auto blend (stack)
This will make layer masks and create final
Flatten layers and congratulate yourself on an impossible shot.
© N. David King
Digital Depth of Field
Extending Depth of Field Digitally
 T-t-t-t-that’s All there is to it…!!!
 You can download a copy of this Powerpoint
presentation and a datasheet on the process
in the Photo 204 section on the SDCC page
of my web site:
www.ndavidking.com/sdcc.htm
© N. David King
Digital Depth of Field
Extending Depth of Field Digitally
QUESTIONS?
© N. David King
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