AO Darkfield 1096 Condenser

[MikeBradley]

I have this AO1096 cardioid darkfield immersion condenser on an AO110 microscope and I'm finding it very hard to centre, at any magnification level. The poor darkfield results I get seem unaffected by whether I use water or oil, the manufacturers literature simply says "immersion". So my question is what steps do people follow to centre this sort of condenser? Thanks

Michael

[apochronaut]

It's oil and must be. There should be a circle visible when looking at the upper surface of the condenser. Using 10X , bring the oiled condenser up to contact the slide( it is better if the slide is a little thicker than the standard 1mm but that shouldn't affect the results the way you describe), then focus on a subject. Center the circle in the field. You may need to slightly rack the condenser up and down a bit to get a good focused circle. At this point, you should see that the illumination circle is fairly symmetrical around the centering circle. If it is not, then you may have a problem with condenser list....... Oh no. Not condenser list! anything but condenser list. It could be worse, it could be the dreaded condenser dive. Either way , on the x axis or the y axis the condenser needs to be level with the face of the objective. You can get away with it in BF but not DF.

The other thing is, if you are trying to use it for 100x DF, a 110 is barely able to kick out enough lumens to get a decent image.

This is a toric condenser. The toric lens needs to be in the bottom and the right way around. The center needs to be a depression not a peak, otherwise the lens has been installed backwards.

[MikeBradley]

Thanks apochronaut, I have followed your guidance and got a very acceptable result, I was only trying it at 40x. I think i had been too conservative with the amount of oil I'd been using earlier.

I had realised my error in calling it a cardioid type when it is in fact a toric one, and yes the dimple is facing the right way!

Finally, I'd never heard of condenser list before but i expect I'll worry about for ever now. Thanks

Michael

[apochronaut]

Glad it worked. I forgot to mention the noticeable flash of light, once you have made adequate oil contact.
Condensers in drydock can list but it is not of as much consequence. It only becomes a problem once you set them afloat on oil.