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Meniscus Lens vs. Computer Simulation
An inexact test


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, Abramov's article 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.


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.



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