Letter to the Editor
exceedingly poor illustration of this diatom. To justify this criticism, I have intentionally made a photomicrograph of Petrodictyon gemma (Figure 1) with techniques that might be called “retro” instead of “advanced,” as follows: perfectly central ordinary bright-field illumination; white light, completely unfiltered to avoid masking the residual optical shortcomings of the optics used; “dry” condenser, effective NA circa 0.9; and the objective was a Reichert achromatic oil immersion 100/1.3 manufactured around 1912. Te valve of this diatom is always strongly vaulted,
digital stacking would be required to obtain a sharply focused image over the entire valve, but the differences in focus nicely illustrate the “white dot” versus “black dot” settings. Resolution of the striae into puncta is excellent—the results of the “advanced” techniques used for the Piper and Chmela paper were obviously inferior to those that can be obtained with an objective of a century ago.
Authors’ Response Jörg Piper* and Gunther Chmela *
JPu.MP@
t-online.de
Unfortunately, the letter from Mr. Sterrenburg contains
some passages that seem to be rather polemical and not very objective. Nevertheless, we hereby give our comments to his letter.
When reading our article, it is clear for everyone to see that
the standard optical equipment and illumination modes we used (glass lenses, condensers, oculars, digital cameras, bright field, oblique light) were not presented as “advanced,” but rather the various monochromatic astronomy filters described (H-beta, O-III, Solar continuum) were considered advanced. Moreover, it should be noted that mirror objectives (reflecting objectives) are special lenses that can lead to “advanced” optical results in some fields because of their particular optical properties (some catchwords: luminance contrast, achromatism, great working distances, enhanced depth of field). In our view, a method, tool, or technique can be regarded
as “advanced” if it leads to improved or “better” results when compared with conventional means. It also can be called “advanced” if it can improve an already existing method. In our article, the following findings or techniques were mentioned as being “advanced”: 1. Monochromatic astronomy filters are well-suited for improvements of many observations and photomicro- graphs, especially when very fine and low-contrasted details have to be visualized. Te optical design of such extremely narrow band filters is “advanced” (see further explanations below).
2. Green light sources of 546 nm or 540 nm lead to only modest enhancements of resolution and contrast, although they are most commonly used. Narrow-band filters of 500 nm or 480 nm should be preferred for observations in visible light because
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they lead to greater improvements in image quality (resolution, sharpness, contrast). For most tasks, the blue-green, 500-nm filter will lead to the most balanced results (optimized contrast and resolution).
3. Astronomy narrow-band filters used for our technical evaluations cannot be compared with or replaced by “modern” green LEDs because such LEDs do not enhance resolution and contrast in a relevant manner even when declared “monochromatic.”
4. Enhancements of image quality with these filters are superior when compared with the optical effects achievable with immersion condensers.
5. In many cases, the condenser aperture diaphragm can remain wide open, even for very low-contrasted specimens because of the contrast enhancement achievable by monochromatic light filtering with narrow-band filters. Tus, the respective specimens appear in adequate contrast even though the aperture diaphragm is wide open so that any reductions in lateral resolution resulting from a reduced condenser aperture are avoided.
6. For particular tasks, mirror lenses can be used for illumination in luminance contrast. Tis is a new and “advanced” technique awarded the “Microscopy Today Innovation Award” in 2010 [1].
Of course, these “advanced” methods can also be used for other tasks that are not related to diatoms. As clearly explained in our paper, diatoms were just selected as instructive examples in order to demonstrate the potential of the light filters and mirror lenses. Moreover, the described improvements of image quality achievable by our filters are relevant for all optical equipment. Mr. Sterrenburg and other users may work with
doi:10.1017/S1551929511000630
www.microscopy-today.com • 2011 July
References [1] JT Quekett, A practical treatise on the use of the microscope, Hippolyte Bailliere, London, 1848.
[2] W Smith, Annals and Magazine of Natural History 9(2) (1852) 1–12.
[3] A Schmidt et al., Atlas der Diatomaceenkunde, Aschersleben-Leipzig, 1874–1959.
[4] J Tempère, J Brun, P Bergon, PT Cleve, E Dutertre, E Grove, P Miquel, and H Peragallo, Le Diatomiste: journal spécial s’occupant exclusivement des Diatomées et de tout ce qui s’y rattache, vol. 1 and 2, M. J. Tempère, Paris, 1890–1895.
[5] E Frison, L’évolution de la partie optique du microscope au cours du dix-neuvième siècle, Rijksmuseum voor de geschiedenis der Natuurwetenschappen, Leiden, the Netherlands, 1954.
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