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  1. #1
    Mustafa Umut Sarac's Avatar
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    Rembrandt - Leica Relief and Integrated Modulation Contrast

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    I found at Summitar, Elmar, Summicron 3d relief effect or they call 3d pop up effect 25 years ago and I still use Leica. I researched as much as I can to reveal the recipe of optical design methodology and no success at the end.

    I think I know how to create wild 3D effect like below image. I think that might be asked , how can we apply such a technoogy to our lenses.

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    Hoffman modulation contrast has established itself as a standard for the observation of unstained, low-contrast biological specimens. Its innovative technical implementation permits significantly simpler handling and greater flexibility in deployment. The integration of the modulator in the beam path of themodern inverted microscopes allows a wide range of brightfield or phase objectives to be used, rather than a small selection of special objectives. Now, contrast can be modified and optimised individually using freely accessible modulators.

    Modulation contrast

    The modulation contrast is a contrast enhancing method in wide-field microscopy that converts optical gradients or slopes in unstained specimen and live cells into varying light intensities. It was invented by Robert Hoffman in 1975 and employs a slit plate to enable oblique illumination and a modulator for light intensity modulation. Due to the three dimensional appearance of the specimen, main applications of modulation contrast in medicine and life sciences are micromanipulation techniques like ICSI (intracytoplasmic sperm injection) in IVF and cloning and pronucleus injection in transgenics.

    Special components in the light path

    At least two special components in the light path are necessary for modulation contrast illumination. To enable oblique illumination a slit plate is placed in the front focal plane of the condenser. Secondly, a modulator is placed in the back focal plane of the objective. The modulator contains three designated areas with different optical densities: one transparent area, one with 15 % light permission and one with 1 % light permission. Light passing the modulator is by definition called modulated.

    In addition to the above mentioned components a second slit containing a polarizer can often be found in the slip plate. In combination with another polarizer located on top of the condenser of the microscope, this polarizer can be used to control the effective slit opening (by opening the 90° (dark) position) and enable relief effects. Note that the specimen is not located between the polarizers which allows the employment of birefringent plastic or glass vessels. However, the polarizers are not a prerequisite for modulation contrast.

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    Modulation contrast converts phase gradients to brightness gradients

    Many components of cells cause changes in the phase of transmitted light by their innate properties. These properties might be the slope and the steepness of a specific structure, a structure that modifies the rate of change in refractive index or simply changes in the thickness of a given structure. As these properties (e.g. cell thickness) often change gradually over a certain area (instead of changing instantly), the change of the phase of light over this area also occurs gradually resulting in a phase gradient. Phase gradients will diffract the incident light which causes a change in the angle of deflection of the light.

    Due to the oblique illumination that is employed in modulation contrast, the change in the angle of deflection might greatly be affected and the light will pass the modulator in a different area compared to non-deflected light. In the resulting images areas of the cell(s) that are more or less homogenous in turns of slope, steepness, thickness etc. will be displayed in grey. The same is true for the background of the image, as light passing these homogenous areas does not experience a phase shift due to phase gradients in the specimen and will hardly be deflected.

    In a modulation contrast system non-deflected light passes the area in the modulator with 15 % light permission, resulting in grey color for homogenous areas of the cell(s) and the background. When light passes areas of the specimen that cause a phase shift (e.g. changes in the slope of a cell membrane), the light is deflected either to the dark (1 % permission) or the transparent (100 % permission) area of the modulator. As the specimen is obliquely illuminated, the image will appear darker from one side of the gradient (where the light is deflected to area with 1 % permission) and brighter from the other side of the gradient (where the light is deflected to the area with 100 % permission).

    IMC offers more freedom

    In the case of Integrated Modulation Contrast (IMC) the modulator is integrated outside the objective in a focal plane conjugate to the condenser (intermediate pupil) in the beam path . The modulators are mounted on sliders which are inserted into the interpupillary interface on the side of the stand . They are therefore freely accessible and allow the user to easily adjust the contrast as required. Beyond this, it is also possible to use modulators with different transmissions. The slider also features a brightfield position for unmodulated images. Microscopes with IMC have been set up to ensure that the orientation of the contrast (shadow direction of the 3D impression) is identical for all objectives. The spatial impression of the specimen thus remains unchanged when changing objectives or magnifications, so there is no need to adjust the slit diaphragm.


    A fundamental consideration when uncoupling the modulator was that the rear focal plane of the objective can be anywhere within the entire range of the 45 mm parfocality distance. A modulator outside of the objective must therefore be movable by at least that distance. Thanks to the design of the Leica objectives, which is defined by fixed focal planes, deployment in inverted microscopes and fixed magnification steps from 5x to 63x, it was possible to reduce the number of modulation planes to two pupil positions (Figure 6).

    The beam path to the image of the pupil, the so-called intermediate pupil, is designed as a 1x telescope system. The infinite beam path behind the objective is reproduced in the intermediate pupil. As a result, plane-parallel optical modulators of any thickness can also be inserted into the beam path at the intermediate pupil, tilted or untilted, without impairing the position or quality of the image. Stray and false light are minimized by the optimal monochromatic and chromatic correction of the telescope system as well as the extremely low reflection properties of the vapour-deposited grey and dark metal coatings of the IMC modulator.


    Fig. 6: Leica objectives are defined by fixed focal planes. Due to their use in inverted microscopes and due to fixed magnification steps of 5x-63x, it was possible to reduce the number of modulation planes to two pupil positions.

    Individually variable parameters

    The IMC offers plenty of scope for individual adjustment of the modulation contrast. The modulator is adjustable vertically to provide a homogeneous image at all times. Varying stage or buffer solution levels and different positions of the cells within the specimen dish can thus be compensated. Moving the modulator sideways alters the resolution: The further the modulator and the slit diaphragm are moved outwards, the higher the resolution (max. resolution Res = λNA).

    Two modulator parameters affect the strength of the contrast: the transmission and the width of the grey area. Reducing transmission increases contrast. Transmission of 25 %, for example, results in smooth contrast. With a value of around 10 %, the contrast becomes significantly crisper. Varying the modulator width is similarly effective


    Narrowing the grey area results in crisper contrast, while wide modulators soften the overall image impression. The slit diaphragm of the IMC features two openings. The first slit is imaged on the grey area of the modulator, producing the oblique illumination for the modulation contrast. The second slit is covered by a polarization foil (Figure 7). A rotatable polarizer positioned in front of the diaphragm can increase or decrease the 3D effect of the modulation contrast. The polarizer does not affect image quality when working with plastic dishes, as the light is polarized only on the illumination side and no analyzer is used on the objective side. The sizes of the slit diaphragms are matched to the most commonly used condensers.

    IMC is therefore not only suitable for routine examinations of biological material – it is also an excellent tool for demanding applications such as micromanipulation, microinjection or microdissection.

    Advantages of IMC

    Numerous advantages make integrated modulation contrast a widely used method in wide field microscopy. Integrated modulation contrast allows the usage of objectives with magnification factors up to 63X. No special objectives are needed and objectives with high correction (e.g. planachromatic and apochromatic objectives) can be employed for modulation contrast. This results in excellent resolution of details with good contrast and visibility

    Another advantage of modulation contrast microscopy is that, unlike in differential interference contrast microscopy, plastic vessels and dishes can be used, as the polarizers in the light path are located before the sample. Furthermore no Wollaston prisms are needed. This results in moderate costs for a microscope equipped with modulation contrast.

    Reference

    Hoffman, R.: The Modulation Contrast Microscope: Principles and Performance, Journal of Microscopy, Vol 110, pt 3, August 1977, pp. 205–222

    Bernard Kleine, Dipl.-Phys. 1 Thomas Veitinger, Dr. 1
    Leica Microsystems
    Last edited by Mustafa Umut Sarac; 04-02-2014 at 06:00 PM. Click to view previous post history.

  2. #2
    cliveh's Avatar
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    And your question is?

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  3. #3
    Mustafa Umut Sarac's Avatar
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    I think I know how to create wild 3D effect like below image. I think that might be asked , how can we apply such a technoogy to our lenses.
    Read it before post.
    Can you please ask easier questions ? One Apug members request .

  4. #4
    cliveh's Avatar
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    If you know how, pray tell.

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  5. #5
    Mustafa Umut Sarac's Avatar
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    I must think about it and read more. I will report more later. Any idea is welcome. By the way , I found same 3d look at moon mission processed images. I think digital must have an answer but I dont know where.
    Can you please ask easier questions ? One Apug members request .

  6. #6
    Mustafa Umut Sarac's Avatar
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    That image explains everything better :

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    Can we put these two filters , one for front of lens , one back and get it work ?

    Below image is helpful also.

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    Last edited by Mustafa Umut Sarac; 04-02-2014 at 05:40 PM. Click to view previous post history.
    Can you please ask easier questions ? One Apug members request .

  7. #7
    Mustafa Umut Sarac's Avatar
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    Images appear shadowed or pseudo three-dimensional, enhancing visibility because of differences in contrast on either side of a detail. There are no halos exhibited in the image, unlike the images produced with phase contrast optics. Modulation contrast converts phase gradient information into amplitude differences that are very different from the phase relationship variations (and optical path differences) produced by a phase contrast microscope. Use of the dark and gray zones in the modulator produce images that contain varying shades of gray and are devoid of color. It is possible to introduce color into modulation contrast images by producing modulators that have the gray and dark zones substituted for colored zones of equal transmittance values. In this case, resulting images from the phase gradient are rendered in colors with similar gradients having the same tint. Currently, we are unaware of any commercial source of modulation filters that contain colored zones.
    Can you please ask easier questions ? One Apug members request .

  8. #8
    Mustafa Umut Sarac's Avatar
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    Above papers indicates three dimensional look is the result of differencing contrast of either side of detail.

    May be ray tracing is the only way to design such a lens. May be Leica and its followers put a little offset of light travel in to their lenses to create a slit and modulator effect . I will report more.
    Can you please ask easier questions ? One Apug members request .

  9. #9
    AgX
    AgX is offline

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    For an understanding of Hoffman Modulation Contrast see here too:

    http://www.leica-microsystems.com/sc...by-step-guide/

  10. #10
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    Am I correct that such a system depends on illumination with polarized light and would therefore not work with most types of photography?
    Trying to be the best of whatever I am, even if what I am is no good.

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