Laser beams at night?

**Falstaff** · 05-11-2009, 07:21 AM

A customer has complained of seeing 'laser-like' beams when looking at street lamps, car headlamps etc. in the dark. I have examined the lenses and the AR coating seems adequate on both surfaces. I can, however, see green, elongated, images when I look through the lenses at an inpection lamp in my darkened test room. There are three line-like images in the lower part of each lens (varifocals), which can join up into one long, sinuous, vaguely horizontal, line.I have not yet been able to observe the effect in other lenses.

Has anyone else had such complaints? Presumably, under such harsh lighting conditions, it is possible, despite the anti-reflection coatings, to see a doubly reflected, highly distorted, image of a very bright light against a dark background. Or is there something else going on here? (the lenses are free form generated).

**chip anderson** · 05-11-2009, 08:51 AM

Poly?

**Falstaff** · 05-11-2009, 09:23 AM

We don't know the lens type because we do not recognise the engravings. However, they are definitely not polys. They are 1.5 index transitions of some sort.

**Jacqui** · 05-11-2009, 10:31 AM

Without looking at them, I can't be certain. However I would look at the AR coating first, it could be faulty.

**Wes** · 05-11-2009, 05:59 PM

Could it be an ar crazing?

**fjpod** · 05-11-2009, 07:21 PM

I've had similar complaints from patients in the past and we traced it to almost microscopic "cracks" in the AR due to chucking and edging pressures. We actually had to look at the lenses on a slitlamp to see the defects. We thought the patients were crazy before we foud it out. Since then, we have improved our edging techniques with AR and no further problem. Put the lenses in the slitlamp and look for cracks or striations on the front or back surface. BTW, this only happens on moderate to high minus lenses.

**HarryChiling** · 05-11-2009, 09:37 PM

Originally Posted by Falstaff

A customer has complained of seeing 'laser-like' beams when looking at street lamps, car headlamps etc. in the dark. I have examined the lenses and the AR coating seems adequate on both surfaces. I can, however, see green, elongated, images when I look through the lenses at an inpection lamp in my darkened test room. There are three line-like images in the lower part of each lens (varifocals), which can join up into one long, sinuous, vaguely horizontal, line.I have not yet been able to observe the effect in other lenses.

Has anyone else had such complaints? Presumably, under such harsh lighting conditions, it is possible, despite the anti-reflection coatings, to see a doubly reflected, highly distorted, image of a very bright light against a dark background. Or is there something else going on here? (the lenses are free form generated).

This issues is indicative of cracks or crazing. If you go into a photography store and ask them to look at a starburst filter you'll understand why this is happening.

**Falstaff** · 05-12-2009, 03:36 AM

Thankyou. There is certainly faint crazing on the upper corners of both lenses but which is very difficult to see. There are indications that the lenses have been glazed too tightly in the frames. I will have a closer look for more extensive crazing across the rest of the surfaces.

Best Regards,

Falstaff.

**Georg Mayer** · 05-12-2009, 04:08 AM

Find an old slide projector and, with no slide in, place the lens right in front of the objective where the beam is very bright and nearly parallel.
Start rotating the lens, you will find two positions, 180 deg offset, where the cracks will show up if they are present.

Before doing this clean the lens thouroghly with meths or spirit, some greasy oily streaks with parallel orientation on the lens (caused by wiping directional with any dirty rag ) can also cause similar spiky hazy effects around light sources, but to a lesser degree.

Thinning prism can also cause internal reflections which might show up as a line of green (if the AR is green) dots, fading away from the light source in one direction only, contrary to spikes caused by cracks/lines going off both ways off the ligth source.

Georg

Better Best than Biggest

**Falstaff** · 05-12-2009, 04:34 AM

Thanks. Will try.

Regards,

Falstaff

**Chris Ryser** · 05-13-2009, 11:57 AM

Originally Posted by Georg Mayer

Find an old slide projector and, with no slide in, place the lens right in front of the objective where the beam is very bright and nearly parallel.
Start rotating the lens, you will find two positions, 180 deg offset, where the cracks will show up if they are present.

Georg...............why don't you tell our friends on Optiboard where you are actively working, they might have little more respect and believe you more.

I am not going to give it away, but your advise is always very constructive and usually right on.

**chip anderson** · 05-13-2009, 12:24 PM

And then there is (was) the Modern Arc. Designed for just such problems.

**Georg Mayer** · 05-15-2009, 07:44 AM

....it crossed my mind when I joined, but at the time I thought rather earn credentials through helpful participation first.
Anyhow, my work base i.e. Lens manufacturer in Munich / Germany and my signature slogan gives it practically away.....I am at Rodenstock
responsible for special projects in engineering, here my email:georg.mayer@rodenstock.com

Have a good weekend, and thanks for feeling welcome here.

Better Best than Biggest