oblique illumination- Schlieren photography

[Rene]

Came across a video that explains some parts of contrast enhancement by oblique and annular illumination:
https://www.youtube.com/watch?v=px3oVGXr4mo

Best wishes, René

[the_playstation]

Helo Rene.

This video is very interesting and we can see things, who are normaly unvisible. I have try this with two of my teleskop mirrors but for spectacular videos and pictures, you need a big parabolic mirror with 1 meter diameter. Sorry about my bad english.

Best whishes and regards Jorrit.

[Paul Keller]

I reckon the original work on Schlieren under the microscope is a contribution of R.W. Wood, in the Philosophical Magazine, Vol.50 (1900), p.347: 'An Application of the Method of Striae to the Illumination of Objects under the Microscope'. Unfortunately I could only lay my hands on this reference amongst my papers, rather than the original text. An interested party will undoubtedly unearth it somewhere. Hopefully, this will help in the endeavour.
Regards,
Paul

[Rene]

Thanks Jorrit, wow, a 1 meter mirror, I would love to try that!
Hi Paul, I guess annular illumination is a kind of Schlieren. I'm pretty sure that it was in common use around 1900, the victoreans loved their diatom dotting. But I'm curious what Wood had to say about it.

Thanks, best wishes,
René

ps replies in german welcome!

[the_playstation]

Hallo Rene.

Die Schlierenfotografie ist dem Foucault Test sehr ähnlich, mit dem man feinste Unebenheiten auf einem Parabolspiegel erkennen/sichtbar machen kann. Nur werden hier feinste Unterschiede der Lufttemperatur, Luftdichte sichtbar gemacht. Mit dem Fouccault Test ist man in der Lage, Abweichungen der Spiegeloberfläche darzustellen, die im Normalbetrieb (z.B. eines Teleskopes) bedeutungslos wären. Ich habe Ihn benutzt, um selbst einen Spiegel per Hand zu schleifen.

Liebe Grüße Jorrit.