How to quantify an unknown GRIN lens?

[DanBarlow]

I have a row of gradient index lens cylinders from a LED print head "laser" printer.

They were almost-contact aligned with the LED strip and very close to the image drum as well. Back focus is going to be <2 mm and front focus <2 cm.

Other than setting up an optical rail with an illuminated test image and screen, (and a microscope to see the resulting image) is there another test I can do to characterize them? They might be good collimating lenses due to short FL? I will be trying one with the blue diodes just to see what happens.

[Jem]

Take the lenses to a local Optometrist/Eye Doctor and ask them to 'neutralise' them on a Focimeter. They will then give you the strength of the lenses in diopters. It's then a very simple calculation to convert this to focal length.

The only problem would be if the strength of the lenses was over 25 diopters as that's usually the maximum strength that a standard focimeter can measure.

Cheers

Jem