Based on a previous question is this the difraction limit of our microscope? , I got the idea to use a true white parallel back light to illuminate an object for measurements (target accuracy is 1 micron). At the moment I'm using a white LED backlight but the image quality is not as good as I hoped due to diffraction. A true white light source should improve this.

In my mind, I would need a ie 100 Watt halogen light, a pin hole and then some lenses to create the parallel beam (I'm ignoring any heat problems at the moment). But google gives me very little results on the subject. Maybe this is not how it's done in the real world?

My questions;

  • What would be the best way to create a true white parallel light beam, diameter 3cm?

  • I don't find any references for true white parallel light. All I find are LED based. Is this so?

  • If true white light is not used that often, maybe it's not so important for image quality? Maybe I should focus more on things like the optical quality of components / alignment / focus /..?


1 Answer 1


This is common requirement in microscopy and this method of illumination was found in the 1890s by August Köhler.

Have a look at this page on Köhler illumination.

  • 3
    $\begingroup$ You should probably include a summary of Köhler illumination: I always think of Köhler illumination as collimating each point on the source lamp at the sample, so that the sample plane is the Fourier plane of the source lamp plane. $\endgroup$ Feb 25, 2018 at 13:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.