Increasing Depth of Field of
Micro/Macro Lens with Helicon Software
The most
inventive machine on the planet is the human mind. It never stops
being curious and never stops coming up with creative solutions to
problems. So it should not come as a surprise that technology, in
the form of a software product called "Helicon Focus Lite" (www.heliconsoft.com),
has addressed and mainly solved the shallow depth of field problem
when using a macro/micro lens at small or moderate reproduction
ratios (see below). Here the terms micro or macro mean the same type
of lens, those used in close-up photography. To give you some idea
just how marvelous this piece of software is, let’s look at some
flower petals which are of low to moderate contrast and very
difficult, at least for me, to even manually focus sharply.
If Image B
does not impress you, think about this. At a focal distance of 16
inches, the depth of field of the Nikkor 105mm is about 0.1875
(3/16) inches (~5mm). From front to back the petals span 1.5 inches
and that’s why just about everything in Image A, except the outer
edge of one petal, is out of focus whereas most of Image B is in
focus; look at the edges and you will see what I mean. The results
are not 100% perfect, but I never look a “gift horse in the mouth”.
OK, I hope you are excited so let’s get into some technical jargon
so you can understand a little about the limitations of sharpness
for a macro/micro lens.
The depth of
field (DOF) depends on the aperture setting and focusing distance.
With zoom lenses it is still essentially the case but changes in the
focal length give different magnifications which make it appear that
the depth of field has changed - it stays virtually constant as you
zoom in and out. Now a macro-lens has very small depth of field at
focal distances of around 3 feet (~1m) or less. At focal distances
of 1 foot or less (<= 0.3m), the depth of field is essentially in
fractions of an inch (0-5 mm) or close to zero from f/4 to f/22..
All this translates into the simple fact that when photographing
close-up of a non-planer object (something other than
a flat surface, say a flower or insect), those portions of the image
closer or further away from the point where the lens focused will be
out of focus. I like the creative possibilities of out-of-focus
images but I also like the idea of subject matter being sharp and
crisp when I want it to be sharp and crisp. Yes, maybe I am spoiled
but now everyone can be spoiled using Focus Lite. Well, let’s turn
to the depth of field for 105 Nikkor to see what we were up against.
Note I used the past tense here.
Depth of Field Charts for 105 Micro Nikkor;
To
demonstrate this easy-to-use software, we will employ a Nikkor
105mm f/2.8 Macro lens. Let‘s get a view of just how limited the
depth of field can be then apply the Focus Lite software.
These charts are from actual data from that lens:
Now that we
have briefly explored depth of field and what a typical macro/micro
lens has for depth of field values at various focusing distances,
let’s turn to setting up the equipment and see how to use Focus
Lite.
How To Take
Images and How to Use Helicon Focus Lite
Camera Setup
and Sequencing Images:
1. Camera
must be on a sturdy tripod with a cable release. The camera
must not move during image taking with Focus Lite.
2. TURN
OFF THE Auto-focus; focus manually.
3. Focus
on the portion of the object that appears closest to the camera. If
you can focus on an edge or where there is good, but narrow,
contrast separation (light/dark, dark/light), it will help you focus
more accurately. For me this is the hardest part with today’s DSLR
cameras, focusing without using the camera’s auto-focus capability.
4. Once
in focus, trip the shutter then refocus slightly further into the
object and snap the shutter again. Repeat this process as you step
through the object from front to back.
Recommendations:
A. Use an aperture of f/14 or smaller,
even f/22, but be careful at very low apertures; increased
diffraction of light at very low aperture reduces sharpness.
B. When stepping through the object, try
to maintain some level of overlap between sections focused on. Do
not blur out completely one adjacent section from the next section
but keep partial sharpness in the overlap between sections. This is
important to do otherwise the software won’t perform well. By
partial sharpness is meant, not fully blurred out.
C. Don’t worry about taking too many
shots; worry about too few. The number of shots depends on the
f/value and the depth of field, which, in turn, depends on the focal
distance used. The smaller the focal distance and hence the depth of
field, the more shots are needed. In some cases, 2 or 3 shots at say
f/16 or f/18 are needed and others times, at closer focal distances,
usually at 1.5 feet or less 6 or more shots are needed.
D. Avoid low f/values, (large apertures)
below f/8 and short focal distances, it appears to be very
difficult, if not impossible, to get well focused steps when the
focal distances are small and the f/value is small. How do you
separate 0 from 0 for depth of field???-you get my point!
With these recommendations in mind, the next
section is a step through example using Focus Lite and a flat desk
calendar as the object. This way one can easily follow the focused
points used and contrast is optimum, black and white with pink mixed
in.
Using Helicon
Focus Lite
Camera and
Calendar Setup:
1. Five
shots were taken with camera setup shown below.
2. Point
A is the number 27 on the calendar and point B is the number 6
barely legible in the first shot, Image C.
3. Shots
were taken with the lens focused on the numbers 20, 13 and 6 were
focal points and mid-way between 13 and 6.
I won’t go
into all the details of how Focus Lite works but will explain the
simple steps to get good results when using this very handy program.
Ok, let’s
see how we actually did. The span actually seen by the lens-sensor
combination is not 8 inches from the number 27 to number 6, but 6.9
inches due to the 30 degree tilt of camera lens. Nonetheless we are
talking almost 7 inches as a needed depth of field to get sharpness
throughout. According to Nikkor’s DOF tables for 105mm Micro-lens,
the depth of field for our camera-object settings is approximately
0.75 inches and here, we are talking roughly seven (7) inches for
the depth of field to cover the calendar span. Well, did we? One
only has to look at Image E. I say Focus Lite did an admirable job,
but the focusing wasn’t too bad either! To really appreciate how
well this Focus Lite does, just look at Image F. It is an enlarged
area around the number 6 of Image E. You can actually see the
separation of dots in the gray dotted-line - nothing is blurred out.
This is credit to the lens and Focus Lite.
I highly
recommend Helicon's Focus Lite if you want sharpness throughout your
macro lens close-ups. You can purchase an annual license for $30 or
a permanent license for $115 as stated in the Helicon web site as of
2009. Well, we now have the best of both worlds: close-ups that are
sharp throughout or, if we so choose, ones that are only partially
sharp - who could ask for more.
Kind
regards,
Joseph. R.
Votano |
