Laser damage risk

Russell Proulx · Mar 11, 2019

I hope this isn't an inappropriate question for this forum.

I've read warnings regarding the risk of damage to a camera sensor (especially mirrorless) when photographing stage shows that use lasers as well as the same risk when photographing autonomous automobiles which use a spinning laser on its roof.

I read more on the issue at the International Laser Display Association's website :

http://www.ilda.com/camera-sensor-damage.htm

But something written on that web page has me wondering if and why it's accurate and assume there are smarter folks than I on this forum who can explain it.

"SLR camera and binoculars warning : Photographers who use an SLR or DSLR camera should not look through the viewfinder directly towards the laser projector output...."

I can understand the risk of viewing a laser using a mirrorless camera and binoculars (or using Live View or shooting video with a DSLR). But why is there a similar risk looking through an SLR's viewfinder?

The prism of an SLR camera is displaying the back of a screen onto which the focused image is projected. It's not focusing the image on your eyeball. Why would viewing something in an SLR viewfinder be any more risky that viewing anything projected on a rear projection screen?

Timmyjoe · Mar 11, 2019

An SLR or DSLR passes the light coming in through the lens, directly to your eyeball.

The light enters the lens, bounces off the mirror, then projects onto, and thru, the ground glass/focus screen, and then proceeds thru the camera prism and out the viewfinder eyepiece. If your eye is in front of that viewfinder eyepiece, the laser beam will go into your eye.

Best,

-Tim

rokoko · Mar 11, 2019

Via view finder on a SLR/DSLR: direct into your eye with high energy. If you take a shot, sensor damage as well.

Via screen: damage sensor only.

Russell Proulx · Mar 11, 2019

rokoko said:
Via view finder on a SLR/DSLR: direct into your eye with high energy. If you take a shot, sensor damage as well.

Via screen: damage sensor only.

That's not what's happening when you shoot with a view camera. Focusing the sun on the ground glass is not the same as focusing it on your eyeball. What's the difference between a 4x5 camera's ground glass and the small ground glass in a DSLR??

You don't burn a hole in your eyeball (or set it on fire) when the sun is in the scene you're shooting. But if you use a lens to focus that same sun on a sheet of paper it catches fire. But watching the paper catch fire does not harm your eyesight.

beatboxa · Mar 11, 2019

Russell Proulx said:
I hope this isn't an inappropriate question for this forum.

I've read warnings regarding the risk of damage to a camera sensor (especially mirrorless) when photographing stage shows that use lasers as well as the same risk when photographing autonomous automobiles which use a spinning laser on its roof.

I read more on the issue at the International Laser Display Association's website :

http://www.ilda.com/camera-sensor-damage.htm

But something written on that web page has me wondering if and why it's accurate and assume there are smarter folks than I on this forum who can explain it.

"SLR camera and binoculars warning : Photographers who use an SLR or DSLR camera should not look through the viewfinder directly towards the laser projector output...."

I can understand the risk of viewing a laser using a mirrorless camera and binoculars (or using Live View or shooting video with a DSLR). But why is there a similar risk looking through an SLR's viewfinder?

The prism of an SLR camera is displaying the back of a screen onto which the focused image is projected. It's not focusing the image on your eyeball. Why would viewing something in an SLR viewfinder be any more risky that viewing anything projected on a rear projection screen?

I skimmed the link but didn't read it thoroughly. Here's my take:

Viewing lasers through an EVF or LCD is not as dangerous to your eyes (though it is for your camera). The EVF or LCD can only get so bright.
Viewing lasers through binoculars is definitely dangerous to your eye. Primarily because it will take an already intense beam and concentrate it to make it even more intense.

Regarding SLRs, yes, it's still dangerous. And part of the answer lies in enlargement and the nature of the laser beam. Also remember that not all lasers are created equally. A super powerful green laser will probably be more dangerous than a weak red laser pointer.

They mentioned something about a lens gathering much more light than the human eye. While this can be true, things are a bit different with lasers. Lasers primarily have a concentrated beam--and this will generally be the same intensity regardless of the aperture (because the beam itself only hits a finite amount of the glass). The lenses may gather marginally more light from the outskirts (as you can still see that a laser is on even if the beam is not aimed directly at your eye), but this light will contribute much less to the intensity. The beam itself is what you primarily need to be weary of, and this will go right through the aperture if aimed as such.

But how intense will it be? This will depend on quite a bit. Let's assume a 50mm lens, of any aperture. Most SLR viewfinders will attempt 100% brightness at a magnification around 0.7x. This would mean they lose only 1 stop of light to the AF mirrors & focusing screen (where it is then diffused). A laser's intensity minus 1 stop is still enough for damage. In this case, it could just damage a smaller area. Yes, it is diffused, but by how much? Probably not enough to prevent injury. Unless the entire focusing screen uniformly turns green (or red or whatever). But this is unlikely--you'll have a hot spot where the beam is aimed.

This may sound counter intuitive, but a longer lens would probably be "safer" (still super dangerous) than a wider angle. The long lens will at least spread the beam out more (reducing its localized intensity), while the wide angles will concentrate the beam more. This enlargement is same reason that a magnifying glass and the sun can burn through wood and other things--what you're doing is projecting an image of the sun onto the wood. The image, however is concentrated from a larger area--this would be what wide angles do to a laser.

You can even test this by taking a laser and shining it onto a wall using various focal lengths. What you'l see is that a wider angle will brighten the beam but make it smaller; while a longer lens will enlarge the beam while making it dimmer.

Marianne Oelund · Mar 11, 2019

Russell Proulx said:
"SLR camera and binoculars warning : Photographers who use an SLR or DSLR camera should not look through the viewfinder directly towards the laser projector output...."

I can understand the risk of viewing a laser using a mirrorless camera and binoculars (or using Live View or shooting video with a DSLR). But why is there a similar risk looking through an SLR's viewfinder?

The prism of an SLR camera is displaying the back of a screen onto which the focused image is projected. It's not focusing the image on your eyeball. Why would viewing something in an SLR viewfinder be any more risky that viewing anything projected on a rear projection screen?

Personally, I wish they'd just ban the use of powerful lasers at shows. They were a bad idea to begin with, and are completely unnecessary.

The problem with looking through an SLR viewfinder, is that many lenses will greatly increase the brightness of the laser image projected onto your retina. A laser beam hitting your naked eye from a distance has some spread to it, so that the size of your iris will limit the energy that is passed.

In dim lighting, typical iris diameter is about 6mm. Using a 50mm lens at f/2.8 (no need to consider wider apertures than that since viewfinders are limited to f/2.8 angular spread), the aperture for gathering light is 18mm. That could potentially send 9 times as much laser energy to your retina. At longer focal lengths it's even higher: A 200mm f/2.8 lens could gather up to 140 times as much laser energy than your naked iris. Damage to your retina could occur almost instantly.

The same light-gathering gain applies to binoculars and telescopes and shows why catching a glimpse of the sun through them can cause eye injury.

beatboxa · Mar 11, 2019

Marianne Oelund said:
Russell Proulx said:

"SLR camera and binoculars warning : Photographers who use an SLR or DSLR camera should not look through the viewfinder directly towards the laser projector output...."

I can understand the risk of viewing a laser using a mirrorless camera and binoculars (or using Live View or shooting video with a DSLR). But why is there a similar risk looking through an SLR's viewfinder?

The prism of an SLR camera is displaying the back of a screen onto which the focused image is projected. It's not focusing the image on your eyeball. Why would viewing something in an SLR viewfinder be any more risky that viewing anything projected on a rear projection screen?

Click to expand...

Personally, I wish they'd just ban the use of powerful lasers at shows. They were a bad idea to begin with, and are completely unnecessary.

The problem with looking through an SLR viewfinder, is that many lenses will greatly increase the brightness of the laser image projected onto your retina. A laser beam hitting your naked eye from a distance has some spread to it, so that the size of your iris will limit the energy that is passed.

In dim lighting, typical iris diameter is about 6mm. Using a 50mm lens at f/2.8 (no need to consider wider apertures than that since viewfinders are limited to f/2.8 angular spread), the aperture for gathering light is 18mm. That could potentially send 9 times as much laser energy to your retina. At longer focal lengths it's even higher: A 200mm f/2.8 lens could gather up to 140 times as much laser energy than your naked iris. Damage to your retina could occur almost instantly.

The same light-gathering gain applies to binoculars and telescopes and shows why catching a glimpse of the sun through them can cause eye injury.

Just an important point here, along the lines I mentioned in my reply as well (and that i think you hinted at): the amount of light will depend on laser beam size.

ie. a 50mm f/2.8 lens will only gather up to 9 times as much light if the beam itself has a diameter of 17mm or more. For the 200mm f/2.8--the laser would need a diameter of 71mm or more (which is a thick beam for a laser).

If the beam is smaller, the lens will gather more light than the laser itself, but not proportionally to the aperture size, as only a small part of the light hitting the lens has the high intensity of the laser beam. The remainder of the lens will capture stray beams diffracted from the laser's exit, which are far less intense than the beam.

Horshack · Mar 11, 2019

Marianne Oelund said:
Russell Proulx said:

"SLR camera and binoculars warning : Photographers who use an SLR or DSLR camera should not look through the viewfinder directly towards the laser projector output...."

I can understand the risk of viewing a laser using a mirrorless camera and binoculars (or using Live View or shooting video with a DSLR). But why is there a similar risk looking through an SLR's viewfinder?

The prism of an SLR camera is displaying the back of a screen onto which the focused image is projected. It's not focusing the image on your eyeball. Why would viewing something in an SLR viewfinder be any more risky that viewing anything projected on a rear projection screen?

Click to expand...

Personally, I wish they'd just ban the use of powerful lasers at shows. They were a bad idea to begin with, and are completely unnecessary.

By unnecessary do you mean there exists a show-lighting alternative to lasers with the same aesthetic as lasers but without their risk? Or do you mean that the aesthetic itself is not worth the risk?

beatboxa · Mar 11, 2019

Russell Proulx said:
I hope this isn't an inappropriate question for this forum.

I've read warnings regarding the risk of damage to a camera sensor (especially mirrorless) when photographing stage shows that use lasers as well as the same risk when photographing autonomous automobiles which use a spinning laser on its roof.

I read more on the issue at the International Laser Display Association's website :

http://www.ilda.com/camera-sensor-damage.htm

But something written on that web page has me wondering if and why it's accurate and assume there are smarter folks than I on this forum who can explain it.

"SLR camera and binoculars warning : Photographers who use an SLR or DSLR camera should not look through the viewfinder directly towards the laser projector output...."

I can understand the risk of viewing a laser using a mirrorless camera and binoculars (or using Live View or shooting video with a DSLR). But why is there a similar risk looking through an SLR's viewfinder?

The prism of an SLR camera is displaying the back of a screen onto which the focused image is projected. It's not focusing the image on your eyeball. Why would viewing something in an SLR viewfinder be any more risky that viewing anything projected on a rear projection screen?

I forgot to mention in my other post: along with lasers, don't view the monsters from Birdbox through either the OVF or EVF/LCD either. They appear to have the opposite effects as lasers on EVF/LCD: they will cause injuries to you without damaging the camera sensor (or cause you to injure yourself). BD Wong knows. Or, he knew.

So basically avoid lasers & monsters with your camera.

Russell Proulx · Mar 11, 2019

Marianne Oelund said:
The problem with looking through an SLR viewfinder, is that many lenses will greatly increase the brightness of the laser image projected onto your retina. A laser beam hitting your naked eye from a distance has some spread to it, so that the size of your iris will limit the energy that is passed.

So is the risk in the brightness of the light itself and not the nature of the light?

As an experiment I just set up a DSLR (D800E) with a 50mm f/1.8 lens, preset the focus to 2 feet and passed my red laser pointer through the lens (from a 2' distance) and placed a small white screen behind the viewfinder. All that comes through is a larger and much dimmer red blob and nothing that resembles the small sharp light coming from the pointer.

If I viewed the laser with my eye to the viewfinder (which I WILL NOT) it would be seen as a very small sharp and bright light source.

When I repeat the same test using binoculars what appears on the white screen is small, focused and very bright light like the original laser.

Sorry if this is tedious. I would just like to understand what I'm missing (other than a few screws <g>).

Thank you for your time in helping explain the issue!

Russell Proulx · Mar 11, 2019

beatboxa said:
Most SLR viewfinders will attempt 100% brightness at a magnification around 0.7x. This would mean they lose only 1 stop of light to the AF mirrors & focusing screen (where it is then diffused). A laser's intensity minus 1 stop is still enough for damage. In this case, it could just damage a smaller area. Yes, it is diffused, but by how much? Probably not enough to prevent injury. Unless the entire focusing screen uniformly turns green (or red or whatever). But this is unlikely--you'll have a hot spot where the beam is aimed.

I think I'm understanding. Thanks for taking the time to write such thorough explanations.

rokoko · Mar 11, 2019

Russell Proulx said:
beatboxa said:

Most SLR viewfinders will attempt 100% brightness at a magnification around 0.7x. This would mean they lose only 1 stop of light to the AF mirrors & focusing screen (where it is then diffused). A laser's intensity minus 1 stop is still enough for damage. In this case, it could just damage a smaller area. Yes, it is diffused, but by how much? Probably not enough to prevent injury. Unless the entire focusing screen uniformly turns green (or red or whatever). But this is unlikely--you'll have a hot spot where the beam is aimed.

Click to expand...

I think I'm understanding. Thanks for taking the time to write such thorough explanations.

beatboxa · Mar 11, 2019

Russell Proulx said:
beatboxa said:

Most SLR viewfinders will attempt 100% brightness at a magnification around 0.7x. This would mean they lose only 1 stop of light to the AF mirrors & focusing screen (where it is then diffused). A laser's intensity minus 1 stop is still enough for damage. In this case, it could just damage a smaller area. Yes, it is diffused, but by how much? Probably not enough to prevent injury. Unless the entire focusing screen uniformly turns green (or red or whatever). But this is unlikely--you'll have a hot spot where the beam is aimed.

Click to expand...

I think I'm understanding. Thanks for taking the time to write such thorough explanations.

You're welcome. I thought it was an interesting question, so to bring it home, here's an experiment.

First, I took an actual focusing screen. Here's a stock focusing screen from a D750. Note that it is not opaque...it is actually pretty clear. Much different than the "paper" experiment.

38953e90f31249dfaf78dfa635751ba6.jpg.png

Then, I propped it up (very gently, because these things are crazy delicate). And I put it up against a some paper against a wall:

590a61c8e5074ef1a6ba0f5d7f84b8fb.jpg.png

And for illustrative purposes, I went with a handheld green laser (532nm)

This is rated at at less than 5mW, a fraction of the power of typical club & concert lasers.

76c40836f59540f7bc80f6aa5347c7dc.jpg.png

Yes, you'd still get injured.

BTW, here's the interesting diffractive pattern produced by the focusing screen:

4b63d86aca0d4a2690bee285f25f2d1c.jpg.png

Also, this is similar to the "telephoto" scenario I described earlier--the same total light spread over a significantly larger area (thousands of times larger) is far less dangerous.

Russell Proulx · Mar 11, 2019

beatboxa said:
BTW, here's the interesting diffractive pattern produced by the focusing screen:

That's the same pattern I saw projected onto the paper screen I was using, though it was vignetted by the size of the camera eyepiece. I assumed that because it seemed diffused that it would not pose a risk.

I've shot a fair number of events were lasers are used on stage or on the dance floor and am only now learning of the risks. Because of my shooting style I rarely have my eye in the viewfinder in those situations,. But I'll now be sure to avoid doing it for safety reasons as well as avoid using live view on the SLR. Using the Z7 will definitely be avoided altogether.

beatboxa · Mar 11, 2019

Russell Proulx said:
beatboxa said:

BTW, here's the interesting diffractive pattern produced by the focusing screen:

Click to expand...

That's the same pattern I saw projected onto the paper screen I was using, though it was vignetted by the size of the camera eyepiece. I assumed that because it seemed diffused that it would not pose a risk.

I've shot a fair number of events were lasers are used on stage or on the dance floor and am only now learning of the risks. Because of my shooting style I rarely have my eye in the viewfinder in those situations,. But I'll now be sure to avoid doing it for safety reasons as well as avoid using live view on the SLR. Using the Z7 will definitely be avoided altogether.

Was your paper right up against the viewfinder or a bit further back? Further back means more enlargement means less intensity.

Here's perspective for you: That same piece of paper should be reflecting everything you see through the viewfinder, not just the laser. The entire frame should be projected onto the paper. But you may not be able to see it because it's so relatively dim. And yet, it's bright enough to be seen when you put your eye up to the viewfinder.

You can test this theory out by putting a lamp or television in the frame and seeing if it projects.

The laser image projected out of the viewfinder is clearly many times brighter than the lamp or the tv.

lapdog99 · Mar 11, 2019

Recent videos show laser used in tattoo removal reflect off the skin and ruin the sensor instantly, if process is being video recorded.

Marianne Oelund · Mar 11, 2019

beatboxa said:
Marianne Oelund said:

Personally, I wish they'd just ban the use of powerful lasers at shows. They were a bad idea to begin with, and are completely unnecessary.

The problem with looking through an SLR viewfinder, is that many lenses will greatly increase the brightness of the laser image projected onto your retina. A laser beam hitting your naked eye from a distance has some spread to it, so that the size of your iris will limit the energy that is passed.

In dim lighting, typical iris diameter is about 6mm. Using a 50mm lens at f/2.8 (no need to consider wider apertures than that since viewfinders are limited to f/2.8 angular spread), the aperture for gathering light is 18mm. That could potentially send 9 times as much laser energy to your retina. At longer focal lengths it's even higher: A 200mm f/2.8 lens could gather up to 140 times as much laser energy than your naked iris. Damage to your retina could occur almost instantly.

The same light-gathering gain applies to binoculars and telescopes and shows why catching a glimpse of the sun through them can cause eye injury.

Click to expand...

Just an important point here, along the lines I mentioned in my reply as well (and that i think you hinted at): the amount of light will depend on laser beam size.

A quality show laser can achieve divergence down to about 1.0-1.2mrad. So the spot diameter will be about 100-120mm at a distance of 100m.

beatboxa said:
ie. a 50mm f/2.8 lens will only gather up to 9 times as much light if the beam itself has a diameter of 17mm or more.

That's a typical laser spot size at about 15m or 50'.

beatboxa said:
For the 200mm f/2.8--the laser would need a diameter of 71mm or more (which is a thick beam for a laser).

That will be achieved at a distance of about 60m or 200' - a distance where one would want to be using a 200mm lens.

Marianne Oelund · Mar 11, 2019

Horshack said:
Marianne Oelund said:

Personally, I wish they'd just ban the use of powerful lasers at shows. They were a bad idea to begin with, and are completely unnecessary.

Click to expand...

By unnecessary do you mean there exists a show-lighting alternative to lasers with the same aesthetic as lasers but without their risk? Or do you mean that the aesthetic itself is not worth the risk?

The latter.

But the risk could be greatly reduced by not allowing the beams to illuminate the audience, or at least not allow them to scan too slowly.

NAG3LT · Mar 12, 2019

Russell Proulx said:
So is the risk in the brightness of the light itself and not the nature of the light?

Mostly brightness and the amount of light. Lasers are special because they make it easy to produce extreme amounts of light and the beam them tightly over large distances. Welding light is also harmfully bright up close, but it is omnidirectional, making it safer to look at from far away.

However, there are special cases. A recent video with the damage from tatoo removal laser involved a laser that produces very short pulses, few nanoseconds or shorter in duration. While their average power may not be very high and they may not look very bright, all their energy is concentrated in an extremely short time window. Thus their peak power can easily be in megawatt range or higher and they are capable of doing localised damage before the heat has time to escape from the spot they hit.

Laser damage risk

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