DIY Phase Contrast

Phase contrast set-ups using the Zernicke method can be an expensive option for the amateur, but home made phase contrast although potentially cheap, at first seems a daunting prospect. Etching phase plates accurately using hydrofluoric acid would be technically difficult and hazardous. In 1953, Prof. Wilska, in a letter to Nature, described the use of phase plates using a sooted pattern on glass. This can either be directly on the back lens of the objective, or on a glass plate, a cover slip for example, mounted close to the objective focal plane. There is a useful Discussion in The Microscope   journal of 1953 describing the technique. This link also gives access to transcripts of the correspondence in Nature.

I found that my Watson 30x and 40x parachromats had a ledge behind the lens in about the right place to mount a phase plate as described in an article from the Quekett Microscopical Club, and having seen other correspondence on this technique, but using a smoked stripe directly on the lens (although this also referred to the use of a separate plate), decided to have a go. I tried using a circular cover slip, applying soot from a candle and and scraping it off to give a stripe, but found this difficult to do in a controlled fashion. I then tried masking the coverslip with adhesive tape before sooting, and this worked quite well, although one needs to select a tape that leaves minimal adhesive residue once removed. The substage stop was made by masking a transparent disc with PVC tape to leave a stripe that aligned just inside the phase plate stripe when the objective back-lens was viewed using a pinhole eyepiece.

Below are some pictures obtained using this type of home-made phase plate with the 40x objective. The first pair show a comparison with darkground illumination

Diatom Olympus FH microscope, Watson 40x Para objective, Olympus P15 ocular

DG illumination

Diatom Olympus FH microscope, Watson 40x Para objective, Olympus P15 ocular

DIY Phase contrast

Collotheca - Olympus FH microscope, Watson 40x Para objective, Olympus P15 ocular

DIY Phase contrast

click on image to see full size picture

Tokophrya - Olympus FH microscope, Watson 40x Para objective, Olympus P15 ocular

DIY Phase contrast

click on image to see full size picture. The currents in the water have been made visible, presumably as a result of very small changes in optical density

A further refinement to the technique is to use an annulus sooted onto the phase plate, with a matching clear annulus in the substage filter holder. This technique works quite well, although making small annuli on a cover slip is quite tricky, so I tried using a smoked spot instead. True, this means that the centre of the objective, which is the best part of the lens, is obscured by the smoked spot, but even so the results were quite promising. This method has the advantage that no separate substage stop is required - the substage diaphragm is all that is needed, closed down to just inside the image of the spot as seen when viewing the objective back lens with a pinhole eyepiece. The pictures below were taken using this setup with a Watson 30x parachromat.

Microscope: Watson Bactil Binocular
Ocular: x8 Compensating
Objective: x30 para
Wilska Phase Contrast (spot)
Camera: Canon Powershot S50

 

Watson Bactil Binocular Microscope
Camera: Aiptek Pocket Cam 3 Mega on 1 eyetube of binocular
Objective: Watson 30x parachromat
Wilska phase contrast (spot)
Ocular: Olympus P15

Watson Bactil Binocular
Ocular: Watson x8 Compensating
Objective: Watson x30 parachromat
Wilska Phase Contrast (spot)
Camera: Canon Powershot S50

This image was passed through a one step Paintshop Pro Enhance Photo routine and then rebalanced for colour.

Next, another comparison:

  1. Conventional, Zernicke, phase contrast, Olympus FH microscope with Gillette & Sibert x40 PH objective
  2. Wilska phase contrast, using a smoked central spot, Watson x30 parachromat, Olympus FH microscope
  3. Wilska phase contrast using a smoked annulus, Watson x30 parachromat, Olympus FH microscope
  4. Conventional brightfield using the Gillette & Sibert x40 PH objective, Olympus FH microscope

 

Finally, here are a selection of phase-plates and substage stops:

At the top, a Watson parachromatic objective (x30), next row a substage phase annulus and clear stripe, and the final row shows three types of circular coverglass smoked phase plate: a stripe, an annulus and a spot. These fit inside the objective behind the lens.

There are more pictures here, which I intend to update as I do more trials.

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