COL

[MicroMan2]

I went to Miscape many times enthralled at this optical technique. Circular Oblique Illumination. While making darkfield stops I emulate the effects at 400x mag. My question is how big should i make the central stop for 4x and 10x objective lenses. My only filter material is cardboard, no clear support or anything. My filter holder diameter is 32mm

[JimT]

My only advice is to experiment. Since it's cardboard if it doesn't work throw it away and make the next one bigger or smaller

[Oliver]

Color the cardboard black, do not use reflective foil or white cardboard. Otherwise the light bulb might overheat due to reflection of the light. The filters that I once used for Rheinberg illumination started to heat up quite a bit, so make sure that whatever material you use, it is heat-resistent. I printed the filters on laser copy overhead transparency and stacked several of them, because the color was not completely dark. This might be less of a problem for microscopes that use LEDs, as there is less heat emitted. You can make the filters with Powerpoint and you can adjust the size of the circles exactly as you need them and then it is possible to easily try out different stop sizes for the different objectives. This way the corners are also sharper than by cutting them out from cardboard (fuzzy edges).
Oliver.

[billbillt]

Thanks Oliver for the tips and instructions...
MicroMan:... I think I started with a dime sized disk and then tried larger and smaller until I was happy with it...

BillT