PWL - Laser pointer: will it damage the camera sensor?

[Kris V]

My granddaughter wants to send a Valentine email to her boyfriend, using a long exposure while drawing a heart on a black background with a laser pointer.
The pointer will not facing the camera. She wants it to look something like the include picture. I tested the exposure time: it will be +/- 15 seconds. Is it safe to use her mom's dSLR?

[Dizzy]

As long as she is facing the blackboard with the laser, I don't
believe you would have any problems. Just be sure and let
her know that the laser never gets pointed at the
camera, and that she should be watchful for reflections.

[Colin Southern]

As long as she is facing the blackboard with the laser, I don't
believe you would have any problems. Just be sure and let
her know that the laser never gets pointed at the
camera, and that she should be watchful for reflections.

+1

[shreds]

Yes, do beware of reflective elements.

[Kris V]

Thanks - I'll make sure she is aware of it. She wants to use black velvet.

[Splatsworth]

Would it be any worse than pointing the camera at the sun?

[revi]

Probably: a laser pointer has an output of 1W or so, in a spot of a few mm^2, that translates to ~20W/cm^2 or 200 kW/m^2. The sun's irradiance is about 1.4 kW/m^2. (very rough figures of course)

And see also this thread about laser damage to a sensor...

[Splatsworth]

I'll take your word for it

[Photon Hacker]

Probably: a laser pointer has an output of 1W or so, in a spot of a few mm^2, that translates to ~20W/cm^2 or 200 kW/m^2. The sun's irradiance is about 1.4 kW/m^2. (very rough figures of course)

The number quoted for the laser pointer is arbitrary. Not only we don't know the power output of laser pointer to be used (Most consumer laser pointers are well below 1 W light output) but the size of the spot probably varies a lot and it's not uniformly lit. These numbers are meaningless anyway, neither of these light sources would usually shine directly on the image sensor, you have ignored the focusing effects of the lens.

I think to use an attenuating filter (Strictly speaking it's not important whether it is natural density because the LASER output is mostly on a narrowband) and increase the ISO sensitivity as need will reduce the risk to the camera. Alternatively, filter-out the main wavelengths of the laser with a specific filter for its type and paint on a fluorescent screen with different dyes forming a pattern or otherwise featured to further reduce risk to the camera and get a colored heart (Can also be done on PP, of course).

[Colin Southern]

a laser pointer has an output of 1W or so

Um, no. Consumer (class 3a) aren't supposed to exceed 5mW. There are a number ramped up ones that go higher, but even a 50mW would be rare for a handheld.

Black velvet absorbs light VERY well - zero chance of damaging a sensor with light reflected from it - however - if any incident light from the laser hits the sensor directly (or via a highly reflective surface - eg mirror / polished metal) then ALL bets are off.

Need to keep ALL lasers away from human eyes too - many are powerful enough to permanantly damage a retina much faster than a blink reflex.

[revi]

Um, no. Consumer (class 3a) aren't supposed to exceed 5mW. There are a number ramped up ones that go higher, but even a 50mW would be rare for a handheld.

Hmm, I have to check my sources better, sorry about that... And thanks for the correction, Colin.

The thread I referred to still stands though, so having the laser hit the lens is a very bad idea..

Black velvet absorbs light VERY well - zero chance of damaging a sensor with light reflected from it - however - if any incident light from the laser hits the sensor directly (or via a highly reflective surface - eg mirror / polished metal) then ALL bets are off.

Need to keep ALL lasers away from human eyes too - many are powerful enough to permanantly damage a retina much faster than a blink reflex.

That's the reason for the special glasses near open (research) lasers. And those are NOT your standard absorbing glasses (like sunglasses or welder's filters).

And for the black velvet: it's diffuse reflection, so that diminishes the intensity quite nicely (and might partially destroy the coherency of the beam). Usually, diffuse reflection is safe, or any use of a laser pointer would be bad for the eyes. I would be careful with the famous glossy black acrylic though...

[Colin Southern]

The thread I referred to still stands though, so having the laser hit the lens is a very bad idea..

Couldn't agree more (assuming the shutter is open).

[Steaphany]

My granddaughter wants to send a Valentine email to her boyfriend, using a long exposure while drawing a heart on a black background with a laser pointer.

She wants to use black velvet.

I recommend that you avoid black fabric of any sort, black absorbs the whole spectrum, so the only laser reflectance that the camera and yours eyes will receive will be a tiny fraction.

I suggest a white cotton sheet, potentially double or triple layered, as a single layer will allow a significant amount of light through to the surfaces behind the sheet.

In a darkened room, the white sheet will be black as your camera will not be receiving much if any light from it.

The spot illuminated by the laser pointer will reflect the laser light brilliantly. Just open the shutter and have her start drawing. She'll get what she draws on a black background.

You never said what intensity laser, one post assumed 1W, but that is an extreme example, most low cost visible red laser pointers are in the 1 to 5 mW ( 0.001 to 0.005 W ) range. Along with the camera lens, do supervise this as the human eye does not fair well either when exposed to laser energy.

[Kris V]

I recommend that you avoid black fabric of any sort, black absorbs the whole spectrum, so the only laser reflectance that the camera and yours eyes will receive will be a tiny fraction.

I suggest a white cotton sheet, potentially double or triple layered, as a single layer will allow a significant amount of light through to the surfaces behind the sheet.

In a darkened room, the white sheet will be black as your camera will not be receiving much if any light from it.

The spot illuminated by the laser pointer will reflect the laser light brilliantly. Just open the shutter and have her start drawing. She'll get what she draws on a black background.

You never said what intensity laser, one post assumed 1W, but that is an extreme example, most low cost visible red laser pointers are in the 1 to 5 mW ( 0.001 to 0.005 W ) range. Along with the camera lens, do supervise this as the human eye does not fair well either when exposed to laser energy.

I don't know the intensity of the laser pointer - She has one of those combination pen/LED light/laser pointers.
She has different coloured pieces of velvet - black, white, dark blue and burgundy. So, you would recommend white, rahter than black?

[Steaphany]

I don't know the intensity of the laser pointer - She has one of those combination pen/LED light/laser pointers.

Then that would probably be in the 1mW range ( pretty much as low power laser that you can get )

She has different coloured pieces of velvet - black, white, dark blue and burgundy. So, you would recommend white, rahter than black?

Yes, in a dark room, White will still be black except for where the laser shines and that will be nicely bright.

[Kris V]

Then that would probably be in the 1mW range ( pretty much as low power laser that you can get )



Yes, in a dark room, White will still be black except for where the laser shines and that will be nicely bright.

Thanks so much for the clarification. We'll probably be playing with it this weekend - see how everything works out.

[danielpower]

The laser beam didn't point your sensor directly,so it wouldn't damage the sensor.

[MilT0s]

So it 's like the painting with light technique but with laser light. That would be interesting.

I have shot high power lasers (100mW) with attenuation filters many times with ccds (photographs and videos) with no problem in scientific research labs. Yours laser is much much weaker so you would have no problems as long as the radiation of specular reflectance doesnt hit your sensor or your eye. However keep in mind that it is possible that the radiation can saturate the sensor. In this case your camera will record white light instead of red (or other colour) but keeping the intensity low you will have no problem. If however that happens the sensor can overheat so keep it in mind! To avoid specullar reflection reaching your sensor keep the camera away from the wall (or black velvet which is ideal) using a tele lens and point the laser from the side at about 45 deg angle.

The most convient way to control the laser light intensity is the light valve technique if you have two linear polariser by choosing the appropriate angle with respect to their axis. Simple polaroid filters suffic for this job.