Kohler illumination in the condenser

[rwb27]

I've started prototyping a more sophisticated condenser module. This uses 3 lenses instead of one, and gets illumination that is brighter and more even than the single-lens condenser (even the tall version in the cantilevered_objective_mount branch). It would be great to integrate this into a nice unit that fits onto the microscope and is easy to keep aligned, but currently it's prototyped with separate lens mounts.

The mounts clip on to the same dovetail used by the cantilevered_objective_mount branch, in illumination.scad. You will need to compile an extra-tall version of it, though.

The mounts themselves are pinched from the openflexure dissection microscope although I should really move this somewhere more sensible.

The arrangement is as shown - aiming for an afocal telescope, where there is one focal length between each lens and the intermediate image/Fourier plane.

[rwb27]

[rwb27]

Update: I remembered the lower focal length incorrectly, it's 5mm and 13mm diameter (with an aperture of about 8mm I think). The order details are below:

[rwb27]

It's worth noting that these lenses are fine in the condenser - but don't expect them to produce a nice image, I tried and they are very far from perfect!

[AlEdwardsUoR]

Nice- like this option, and I had meant to ask if this type of more sophisticated illumination was simple to achieve. Given optics friends have told me illumination is a 'dark art' I am relieved to see this simple and low-cost rig, which should be very useful.

[rwb27]

Sure. In fact, my favourite option at the moment (at least until we have a nice mechanical assembly for the condenser) is the one in the cantilevered_objective_mount branch, which just uses a single lens, and an LED with some white electrical tape (PTFE tape should also work nicely) as a diffuser. It's longer than the one on the master branch which gives it a higher NA, and it's not Kohler illumination but it is close enough for many purposes.

[rwb27]

For the record, the illumination I mention above is now in master. It is not Kohler illumination, but it's critical illumination with a diffuser - which is adequate for most transmission imaging. Proper Kohler illumination would be nice as an option, we'll get there eventually! This might be an interesting project for someone wanting to play with optics a bit.