Simple method to test objective using laser pointer

[Dubious]

Here's an interesting article on using a cheap laser pointer to check objectives for damage. Sounds like a laser pointer is a useful tool to have for anyone who buys used objectives on Ebay. (Sellers often have no idea whether an objectives is damaged.) My procedure is now going to be: (1) examine outside and front of objective with stereo microscope; (2) project laser pointer through it onto ceiling or wall as described in article; (3) install on microscope and examine glass with phase telescope.

https://www.cambridge.org/core/journals ... 498C4A4F81

[MichaelG.]

The principle works very well [maybe too well ?]
… the only problem I have found is that every lens looks dirty !

Setting a threshold of ‘acceptability’ seems to be the tricky bit.

MichaelG.

[mrsonchus]

Very interesting indeed, and oh-so-simple to try! I for one will certainly try this, as progress during cleaning may be observable even measurable if desired. Of course trying for perfection may be a bad idea, but to be able to see any progress would help enormously in the sensible choice of a 'stop point' in cleaning etc as it were.

Thanks for a very interesting and useful post.

[Hobbyst46]

Thanks for the link.

Unfortunately, the serious issues with my ~60 years old objectives are more in the internals, and lens coatings, than dirt on the front lens.
Delamination can be revealed with a stereoscope.
Although the authors of the linked article did not suggest it, I gave the laser method a chance to demonstrate delamination. Quick and dirty inspection of a proved delaminated 40x objective with a 3-5mW red laser pointer. Visually, there was no dramatic change from a non-delaminated 40x objective.

[Dubious]

The laser would, I think, be best at detecting lateral fractures in layers of glass or things that similarly change light transmission when scanned side to side. Since delamination involves glass that is still intact side to side, I'm not surprised it is less useful there, although in some cases there probably would be an indication that something is wrong.

[iconoclastica]

Thanks for the link. I greatly enjoy browsing past issues of this journal that I didn't know before now.