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Edwin's Vignettes
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Macro
Experiment
June 29, 2003
After
writing a short piece on the
Canon 500D
closeup lens , I took to re-reading some parts of John Shaw's
Closeups in Nature book on macro photography. I went
through the chapter on stacking lenses to obtain very high
magnification and wondered if I might be able to do something
similar. There were a couple of concerns though, primarily that I
did not have the same lenses John Shaw recommended for stacking
lenses, namely a 200mm f4 prime as the master lens and a short 105mm
f4 for stacking. It's best if the two lenses are of similar physical
dimensions to allow for easier matching and mating of the lenses.
What
to do? Then I spied the 35-70mm f2.8 and 20mm f2.8 lenses in my
cabinet and my mind went hmm...both lenses have a 62mm filter size,
so that makes them very similar for the physical dimensions, but,
how do I stack them together? There are certainly adapters available
that allow for reverse stacking of lenses, but trying to track one
down would take time and given how specialized such an accessory
would be, perhaps not a great use of funds. John Shaw recommended
just taping the lenses together if high magnification work was just
going to be an occasional thing, so that's what I did.
 No
gaffer tape available, so I used the next best thing, masking tape.
Duct tape leaves a sticky residue that can be a mess to clean off,
even if the tape is applied for a short time and since the 20mm lens
is not my own, best not to mar its perfect finish. I also did not
want to gunk up my own 35-70mm lens either. Oh yes, when stacking
lenses, you reverse the front lens so that the two lenses meet
filter to filter thread. The rear element of the stacked lens then
becomes the front element of your Franken-creation.
How
much magnification is available? Well, the basic formula for the
stacking lens is:
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1000 / focal length of the lens, or in my case, 1000/20 = 50
diopters of magnification, which is huge, because consider that
the Canon 500D is probably no more than a +3 diopter lens
Putting the 20mm lens in front of the 35-70mm (set to 70mm) requires
this basic formula to figure out the magnification available:
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focal length of prime (70mm) / focal length of stacked lens
(20mm) = 3.5X magnification or three and a half times the
subjects true life size
What
kind of subject require 3.5X magnification? Well, you could magnify
anything you want, but I headed out to the garden my dad tends and
looked for some creepy crawlies that make their way into his
watering pail. The insects fly or crawl in and then get stuck in the
water and I suspect that most usually drown, so I had no ethical
qualms about a couple of tiny little critters used for my
photographic experimentation. Today, I only found a few critters,
one was a yellow bug that was less than a 1/4 inch long and a second
was a tiny red bug that was barely larger than the yellow bug's
head. The red bug might have been a water mite, but my shots were
not good enough to compare with the sample shown in John Shaw's
book.
The
sample shots below show just how small the yellow bug is. At left is
a full frame shot taken with my left arm about two-feet away from
the camera and at right is a 100% crop of the yellow bug at the end
of a wooden toothpick. Even a lifesize 1:1 magnification ratio would
not amount to much for revealing the details of the bug.
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 Going
about how to take the shot took a few minutes of adjusting
how high I had to place the subject vis a vis the tripod
mounted D100 camera and the Franken-lens. Working distance
ended being less than two-inches when I set the 35-70mm lens
to its minimum focusing distance. Given the high
magnification and the extremely shallow depth of field,
proper subject placement is critical.
I borrowed my kids Lego blocks to set up a little platform
that got me the general height required with the subject
placed on the back of a B+W plastic filter case. I had to
find some extra pieces of varying height to get the focus
closer to what I needed, and these included a camera mount
cap and the rear lens cap placed under the B+W filter case.
However, focus was still off by an amount smaller than
anything I had available to further stack under the filter
case, but an old magazine placed under the Lego platform did
the trick and got me within a decent focus range.
The sample shot at right shows the basics of my home-brew
macro platform with the exception of the camera, which is
the F100, as the D100 was used to take the sample shot too.
The results were interesting. Stacking lenses causes
mechanical vignetting and gives the appearance that a very
short focal length fisheye lens was used and as one stops
down, the vignetting circle becomes smaller too.
The first shots were taken with just ambient light with the
35-70mm lens set to f5.6. The stacked lens is used wide-open
and together the shutter speed required was 2.5 seconds. The
result is a soft image that revealed that the focus point
desired was still off by a tiny amount and few details can
be discerned.
The next few attempts were with flash being incorporated
into the mix. An SB28DX flash unit connected with the SC17
TTL cord was used and distance for the flash unit was
determined by taking a shot and reviewing the LCD for blown
out highlights. The first shots were very blown out and not
until I moved the flash out to about two-feet away at an
angle that was just slightly higher than parallel to the
subject height, did the results show some promise. However,
even at f22, the focus was still off, as I was unable to get
the yellow bug's eyes sharp.
The red bug was so small that taking shots of it was
essentially a crap shoot using the same technique as for the
larger yellow bug. As you can see below, the results got me
sharp legs but not the body.
Trying to see the subject through the D100 viewfinder was
fraught with problems, as the view was very dim and although
I could see that there was going to be some vignetting, I
could not see just how much there would be. Using the Depth
of Field preview button would have been like trying to view
through the night. And obviously, critical focus was not
possible, or at least with my eyes. To that end, I've
ordered the Nikon 2X DG-2 viewfinder magnifier and adapter
piece to use with the D100 to assist me with better focus
when I wish to do macro photography.
It was an interesting experiment, one that took less than an
hour to do, but one that opened up some previously
unexplored territory for me. The use of digital was key to
helping me see the results of the experiment at various
stages and telling me what I needed to do to get a better
exposure.
f5.6 @ 2.5 seconds - Ambient light exposure
full frame view
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f22 @ 1/60 with an SB28DX set to Standard TTL -
full frame view
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f22 @ 1/60 with an SB28DX set to Standard TTL
50% crop view
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f22 @ 1/60 with an SB28DX set to Standard TTL
100% crop view
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