Natural Science Forum / Physics / Optics / February 2007

Hi

My Zeiss PH1 plate is homemade so pending some accurate measurements
offered from an undamaged one, a central diameter of 3.7 mm and
annulus width 0.4 mm works fine on my 1970s vintage Zeiss stand with
achro / apl phase condenser and Zeiss 10/0.22 Ph objective. The
annulus could do to be a bit bigger if I redo it but works well
enough.

It's possible to measure the desired annulus pretty well with a 'phase
ruler', ie concentric rings of known width printed from e.g. a CAD
package placed in the phase stop plane and the inner and outer annulus
lines determined with a phase telescope. Then print this out blackened
in. Although the PH1 will be the trickiest being the smallest. Ian
Walker has a downloadable 'phase ruler' in TurboCad format on
'Micscape' (3-12 mm in 0.5 mm steps). The condenser focus can usually
take up small errors.

http://www.microscopy-uk.org.uk/mag/imgsep04/phaseruler.tcw

Some hobbyists stick together two back to back printouts to make the
acetate plate denser, athough found on my printer this wasn't dense
enough so painted mine on a slide ringing table feathering the paint
almost but not quite to the annulus edges so that the neat printed out
circle is retained but the black areas are made denser with paint.

Good luck!

regards

David