Meniscus
Lens vs. Computer Simulation An inexact test
Introduction
This
article deals with a single element meniscus lens. Such an optical
scheme is well known for its unique softness, which cannot be easily
simulated with the help of computer tricks. Of course, a lot of painstaking
manual operations can do the job. But straightforward methods invariably
fail to produce the expected soft-focus effect.
I
do not intend to refute such conclusions. The purpose of my test is
merely to illustrate them. I am absolutely sure that a single picture
can give by far more useful information than a lot of boring and lengthy
explanations. With this in mind, let us analyze the images.
Pictures
produced by real lenses
Fig 1. Home-made single element meniscus lens, f = 85 mm, f/4.0
In
Russia, photo amateurs often make home-made meniscus lenses on the
basis of the Helios-44 lenses, which are available on the market at
very low prices (about $10). Those lenses with a 42mm threaded mount
were manufactured in the Soviet Union for the well-known Zenith SLRs.
I also made my meniscus lens from Helios-44.
Even such a small web-image can demonstrate two important features
of the meniscus lens. First, the picture is rather soft. Second, the
bright parts of the image glow. Every white area in the picture is
surrounded by distinct radiance.
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Fig 2. Pentax FA 50/1.4 SMC
This
photograph was produced by a Pentax prime lens.
It was selected as a starting point for my computer simulations.
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The
results of computer simulation
Fig 3. Computer soft-effect
Frankly
speaking, this picture has nothing to do with meniscus lenses. It
just demonstrates how typical computer softness looks like. To obtain
such an image, you will have to create two layers. In the upper half-transparent
layer, the picture should be sharpened and/or its contrast should
be slightly increased. The background layer should be blurred with
help of the Gaussian blur filter.
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Fig 4. Softness based on the Median filter
To
obtain this picture, I substituted the Gaussian blur filter with the
Median filter. In rare cases, the Median filter alone can produce
images that are very close to the pictures taken with a true meniscus
lens. As far as Fig 4 is concerned, we may see that the image still
lacks
the radiance that can be seen in Fig 1.
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Fig 5. An attempt to reproduce radiance
The
effect in Fig 5 was obtained by a procedure described by Vitaly Abramov.
As far as I know, is available only in Russian. However, the essence of
his method is not difficult to understand. He suggested that the Maximum
filter be used to produce rough aureoles. Then they should be smoothed
and blended with the original picture.
Well,
there is some radiance in Fig 5. However, the picture looks a little
bit unnatural. Moreover, the procedure produced several artifacts.
The result is still far from the target picture shown in Fig. 1.
Nevertheless,
I admit that Abramov's procedure is very useful. It cannot completely
simulate the meniscus lens. However, it can be used to produce an
interesting effect.
Conclusions
There
is no point in drawing any simple conclusions from my experiments.
I pursued only one goal — to give you some basic information
on the subject matter. Thus, treat this web page in an appropriate
way.
You
must obtain a written permission from me to use any materials of this
site for any commercial or non-commercial purposes, unless there is
an explicit statement to the contrary.
