"comet tail" grows after turn on

EvoFXDWG · Jul 2, 2017

I have an underwater green unit (like this Underwater Scuba & Dive Green Laser Pointer ) that i have had for a number of years.

I got it out to prepare for an upcoming SCUBA trip and noticed the projected dot, "grows a tail", like classical pictures of an astronomical comet, after turn-on. The "tail" is rougly triangle shaped, with one side arcing and brighter, and covering mabye 15-20 degrees of arc about the center dot. It is always oriented at the same angle wrt an arbitrary point on the circle. There are some other, much dimmer, narrow spikes (not triangles) visible as well, one being 180 degrees from the "comet tail." These spikes also dont appear, or are even dimmer, on initial turn-on. If the unit hasnt been on for a long time, it takes the tail and spikes several seconds to "grow". If it is turned off and immediately turned on, it takes only one or two seconds to "grow". I changed batteries and same result. I had not noticed it doing this until recently.

The regulator board has what looks like a minature potentiometer. I havent adjusted it. I am an electronics engineer but have no experience with lasers.

What is the phenomena I am seeing? Can i fix or improve it?

paul1598419 · Jul 2, 2017

Would be great if you could add a photo of what you are talking about. From your description, alone, it is hard to say.

hakzaw1 · Jul 3, 2017

I never trusted any waterproof laser to be 100% -IMO that is why so many are sold as water 'resistant' or give a limit to depth.
Old style waterproof camera housings had 'O-ring' seals that one must 'grease'=keep clean etc and even then some moisture gets inside.
as said pics can help..
I fear saltwater much more than fresh..takes so little to do damage. its in the air. (copper beware!)

we have some fine members here from your area.. & if I may suggest, .. place an 'intro' thread in our welcome section.. myb check out a few Stickies etc.

I have seen the 'flares' you describe many times lots of kinds, names like 'artifacts' 'moons' 'second dot' (yes they do look like comet tails).. and many causes --some are 'fixable' many are not- those with OCD causing a dire need for perfection. MOld has been known to grow inside/between the lenses. Even sealed.
IMHO must not be very happy with most lasers.

AFAIK no laser diode 'makers' have laser 'hobby folk' in mind--when designing.
Even to he point of making it hard to remove and repurpose the diodes..

I sure we have had threads/posts on this subject.
sure would like to see some pics of your dives/w laser..\& lots of threads on 'cleaning lenses' --

welcome to LPF==+95 < getcha some green bars--lol)

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add-- Im pretty sure you will not see that when using on a dive ...

EvoFXDWG · Jul 3, 2017

hakzaw1 said:
I never trusted any waterproof laser to be 100% -IMO that is why so many are sold as water 'resistant' or give a limit to depth.
Old style waterproof camera housings had 'O-ring' seals that one must 'grease'=keep clean etc and even then some moisture gets inside.
This unit has been down with me on at least 50 dives in the Gulf of Mexico, at max depths of typically 80 feet, with no hint of saltwater intrusion. Yes, i keep the orings clean and lubed.

as said pics can help..
working on that
I fear saltwater much more than fresh..takes so little to do damage. its in the air. (copper beware!)

we have some fine members here from your area.. & if I may suggest, .. place an 'intro' thread in our welcome section.. myb check out a few Stickies etc.
I will soon, but wont be spending much time on here. Lots of other stuff going on. Plus.....i dont need another hobby.

I have seen the 'flares' you describe many times lots of kinds, names like 'artifacts' 'moons' 'second dot' (yes they do look like comet tails).. and many causes --some are 'fixable' many are not- those with OCD causing a dire need for perfection. MOld has been known to grow inside/between the lenses. Even sealed.
IMHO must not be very happy with most lasers.
I thought it might be a clue that i described the phenomena as temporal, growing within seconds from turn on, as if its due to heat or capacitive charge saturation. It seems obvious it is not a mold or growth inside as it is not present at turn-on. Also, i assumed the fact that it takes longer for the "comet tail" to "grow" if it has been off a long time would be a clue.

AFAIK no laser diode 'makers' have laser 'hobby folk' in mind--when designing.
Even to he point of making it hard to remove and repurpose the diodes..
I assumed if it is a circuit problem, or an adjustment (there is a potentiometer on the circuit board), then it might be an inexpensive "tune". These units are now $49 plus shipping so i might replace it (but might go to blue this time) if it is a difficult or expensive fix. I am taking it out this month and will see if its even a problem underwater. It may not be for my use.

I sure we have had threads/posts on this subject.
sure would like to see some pics of your dives/w laser..\& lots of threads on 'cleaning lenses' --
I have played with it on exactly one night dive (it is pretty cool and the boat crew can see the beam moving from topside at night). I have pointed it at some menacing sharks a few times while spearfishing during the day (it doesnt seem to repel them). Other than that, it is usually in my BC pocket or hanging next to my flashlight and i dont take it out while on a dive. Oh i do remember ocassionally, if there are no gamefish around or we are tired of swimming/hunting, I have gotten it out and play with the smaller reef fish. Some species will chase the spot like a cat. I dont take vid or pix underwater these days, just spearfish. One possible lifesaving use is to flag a boat (or aircraft?) down if we get left drifting by our dive boat (Dry Tortugas is about 70 miles west of Key West). Havent used it for that yet thank goodness! Also have used it on the boat at night to point out satellites and constellations in the dark night skies of Dry Tortugas.

welcome to LPF==+95 < getcha some green bars--lol)
Thanks - not sure what you are talking about (green bars?) but i guess i will figure it out.

+++++++++++
add-- Im pretty sure you will not see that when using on a dive ...

I assume you mean the "comet tail" - probably not. I was more concerned about reduction in range due to dispersion of the light energy. Also concerned if the problem gets worse. But unless the water is extraordinarily high visibility (e.g. no turbidity), i probably wont notice and neither will the sharks.

Radim · Jul 3, 2017

Interesting. Seems there might be a dirty or scratched lens or output window, or something else like a bit of salt somewhere (even little one is enough).
Try to rotate your laser to see if the comet tail shape rotates as well, if yes - it is in laser itself (I use this technique how to distinguish which optics part is dirty - if some difraction grating or output lens and so - when I do some laserpainting and get strange pattern etc.). If it does not rotate, that might be some effect of water use or more likely I guess it might be how you see it. Also eyes have some effects how laser dot is seen - you might try it with observing little speckle stars in dot and move your head (looks like dot is a window behind which the speckle stars are) or if you close your eye a little bit to allow your eyelash to cross the light path from the dot. Here also dive mask may have effect as it is additional optic element. Try to rotate your head with static laser to see difference. Picture would be nice, but also try to identify where there is a problem, might not be laser itself...

paul1598419 · Jul 3, 2017

Actually, you need to rotate the focus lens a little to see if it is the lens. Rotating the whole laser won't tell you much. Also, the OP stated it is an artifact that changes with time, so it might be heat related. You don't want to adjust the pot on the driver board as that sets the current the diode runs at and is unlikely to help, but could cause real problems. It should only be set with a dummy load in place of the laser diode.

Radim · Jul 3, 2017

Yes, Paul, maybe I did not write it clearly. I rotate the grating (or any other optic element attached to laser) separately to see what needs to be cleaned. Laser rotation is sufficient to distingush if it is something in laser or some external effect (since optics in water is very tricky AFAIK - I'm also scuba diver). If there is some salt on crystal for example (could pass even o-rings) the output lens needs to be rotated to distinguish it. Picture of dot might help to identify the cause.

Edit: Also does this defect appear when not in water?

hakzaw1 · Jul 3, 2017

@ OP-- even if you can't come back to LPF much --still glad you came & hope we can help.
have a fun 4th..hak

Accutronitis · Jul 3, 2017

A blue laser beam will travel the largest distance through water, Farther then even green......

paul1598419 · Jul 3, 2017

BTW, Happy B D, Len.

Benm · Jul 4, 2017

I suppose this 'comet tail' thing is actually an artefact that was not designed into the unit at all, but you found practical use for. That makes it pretty difficult to say what caused it in the first place, how it changed or how to change it back.

hakzaw1 said:
I never trusted any waterproof laser to be 100% -IMO that is why so many are sold as water 'resistant' or give a limit to depth.
Old style waterproof camera housings had 'O-ring' seals that one must 'grease'=keep clean etc and even then some moisture gets inside.

Waterproof for scuba diving is indeed something very different than water resistant as in surviving using it in the shower or dropping it in a puddle.

Camera housings for scuba diving require diligent maintenance of the o-rings, as do scuba flashlights and lasers. Not only do you need to grease them, but also keep them very clear otherwise, a tiny spec of sand trapped in there will cause them to flood when down 30 meters or something like that.

Laser pointers -intended- for scuba application will be okay, but something just advertised as waterproof or splashproof will certainly fail at such depths. Waterproof without specification means nothing - perhaps that it'll be okay if you drop it in puddle, but it could already fail at the bottom of a swimming pool with 0.2 extra bar outside pressure.

Recreational scuba diving goes down to 30 meters and sometimes briefly deeper, so equipment for that should be able to handle at least 5 bars of extra pressure, which is a gigantic mechanical load on a big flashlight.

Upside is that the water helps a LOT in cooling those things, there are quite some scuba (LED) lights that can only be operated under water without overheating quickly.

Radim · Jul 4, 2017

Benm said:
I suppose this 'comet tail' thing is actually an artefact that was not designed into the unit at all, but you found practical use for. That makes it pretty difficult to say what caused it in the first place, how it changed or how to change it back.

Waterproof for scuba diving is indeed something very different than water resistant as in surviving using it in the shower or dropping it in a puddle.

Camera housings for scuba diving require diligent maintenance of the o-rings, as do scuba flashlights and lasers. Not only do you need to grease them, but also keep them very clear otherwise, a tiny spec of sand trapped in there will cause them to flood when down 30 meters or something like that.

Laser pointers -intended- for scuba application will be okay, but something just advertised as waterproof or splashproof will certainly fail at such depths. Waterproof without specification means nothing - perhaps that it'll be okay if you drop it in puddle, but it could already fail at the bottom of a swimming pool with 0.2 extra bar outside pressure.

Recreational scuba diving goes down to 30 meters and sometimes briefly deeper, so equipment for that should be able to handle at least 5 bars of extra pressure, which is a gigantic mechanical load on a big flashlight.

Upside is that the water helps a LOT in cooling those things, there are quite some scuba (LED) lights that can only be operated under water without overheating quickly.

Yes, this is correct. Just if you have advanced course (PADI) you might go up to 40 m. Still there are very interesting effects on human body (with air in tank like from 25 - 30 m and below). I got high several times from high pressure nitrogen there (and even deeper than 40 m). Very interesting, but very dangerous - there is important to get up immediately or you might loose your reality that you are diving. I observed great peace in myself, heard bubbles leaking like metalic sounds, everything was joyful and my body was like spreading into space. Not bad for air. :crackup: When I realized that I enjoyed it for a half minute or so checking computer for time and started to go up. When I was in lower depth this psychedelic stuff just vanished.

Regarding the stuff like cameras, flashlights etc. They have very heavy and massive cases to sustain the pressure. Still I assume (does not seem massive) this laser OP has is not designed for diving (maybe snorkeling on water surface), so even shallow water might allow at least a bit of water to get in and possibly get into laser - since salt can get everywhere there might be a bit of salt somewhere.

Benm · Jul 5, 2017

Diving can certainly have it's effects on people, at 30 to 40 meters deep you get issues like the ones you describe.

Personally i don't really enjoy the experience too much. I know how to use the equipment and all, but don't like the fact that you effectively get 'trapped' at a certain depth from which it would be dangerous to just inflate your bcd and surface.

I still enjoy snorkeling and some freediving though, enjoying marine life without the idea that i have no choice but to depend on equipment to survive down below or risk caisson disease and such.

As for equipment claiming to be water resistant: if it's not intended for scuba diving, don't count on it. You get things that claim to be 'water resistant' down to something like 10 or even 30 meters, but will flood when you dive down only a few meters for a short period of time.

For something to be water resistant to 30 meters deep it has to be very rugged - the forces on it are 3 times a large as those would be when floating in in space, albeit in the other direction. Just look at proper under water housings for camera's used by scuba divers, those things are extremely strong, to the point where they'd survive an elephant stepping on it (which is in the same order of pressure really).

"comet tail" grows after turn on

EvoFXDWG

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