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Do I need phase contrast?

Found in: Buying Advice

Phase contrast microscopy is an optical staining technique. It converts differences of refractive index of a specimen into brightness differences.

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Advantages of phase contrast:

  • It allows you to better see live, colorless, unstained specimens. Parts of the specimen, which would be otherwise difficult to see because they have the same color, now appear darker or brighter than the background.
  • It produces images which are quite information rich, and rich in details. Cell organelles can be seen much better.
  • Often phase contrast images subjectively look much better than brightfield images. This is partially due to the increased contrast.
  • Phase contrast objectives can be used for conventional bright field, but the image quality will be slightly lower (due to the integrated phase ring in the objectives). All you have to do is to remove the phase contrast filter from the condenser to use the objectives for bright field.

Disadvantages of phase contrast includes:

  • High price. You need special phase contrast objectives and a phase contrast filter. They are quite expensive.
  • Every objective requires its own phase contrast filter. If you switch magnification, then you have to switch the filter. Some manufacturers make special condensers which include a rotating filter holder. This is practical, but really costly and might not be available for all microscope models.
  • Phase contrast filters might not be available for all microscope models, especially for low cost introductory microscopes, which are not very modular.
  • Phase contrast microscopy is less suitable if you want to observe the natural colors of a specimen, or if you are involved in staining. The natural colors overlap with the differences of brightness that the phase contrast optics produce.
  • Phase contrast microscopy is also less suitable for specimens which have a similar refractive index as the mounting medium, as the optics will then not be able to pick up this difference.

Do I now need phase contrast?

If you are asking this question, then probably the answer is no. You would know when you “need” it. If you want to observe mostly ready-made permanent slides, which are stained, then you might be better off with bright field optics. If your interests are more on the observation of live, unstained eukaryotic cells, then phase contrast does offer advantages, but is not a necessity for casual observation. It depends much on what you want to observe and what your expectations are. If you want to mostly observe unstained bacterial cells, then a 100x oil immersion phase contrast objective is highly recommended. I do not even want to know how much this would cost…..

Alternatively, it might be better to spend the money on a more modular and stable microscope body or on a camera and adapter. The cost of phase contrast objectives and filters can easily surpass the cost of a whole microscope body. Having said that, I would qualify my own opinion somewhat. I personally would prefer to have a low power (10x) phase contrast objective and associated filter than a high power 100x oil immersion bright field objective, simply because I do not use the 100x bright field objective very much. I do not need the magnification. Alternatively you might want to invest the money into buying a more stable microscope with a binocular/trinocular head.

If you do intend to experiment with phase contrast (and other techniques) in the future, then I would more carefully select the microscope manufacturer and microscope body. Get information on the availability or parts and modularity of the microscope so that you are not stuck with a microscope which can not be expanded.

Most amateur microscopists do not have phase contrast and also the introductory microscopes of schools and colleges do not have them. Bright field optics will keep you busy for a life time. But then on the other hand, phase contrast images do look pretty nice!

Brightfield phase contrast

Left: bright field image; Right: phase contrast image (credit: Public domain image by GcG)

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