# Telescope mounted Green Laser Pointer problem.



## brucepeter2002 (Apr 25, 2006)

First post here asking for advice. I have aquired a pen type green laser pointer which is about 15mW - works well. I made an adjustable mount so it could be installed on my telescope for initial star alignment to save trying to get into awkward positions trying to set up the position of the initial alignment stars.
It is not used for anything else and is ideal for what I intended...
After making a neat mount and istalling it onto my 10" scope I find that the lasers power output was a fraction of normal. After a short investigation this is clearly due to the outside temp, even at 10C the units power is bad. Suspected batteries so kept unit outside then changed batteries for warm ones but the problem is still there so its not the battery which is the problem (2x AAA).
Bring the laser inside so it warms up and its back to normal output.
I have now insulated the case and this helps but does not cure the problem.
Is it normal for this type of laser to be so temp sensative and is there a way around the problem or am I just unlucky...
Any help please gratefully received.
Peter


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## crampedson (Apr 25, 2006)

Lasers should not be quite so sensitive to temperature fluctuations, in fact, the laser should get brighter as the temperature decreases due to a higher efficiency in low temperatures. In addition, there is a photodiode in all green lasers used to keep the light output constant, despite conditions. Your laser's photo diode may be acting up due to it being cold.


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## EGP (Apr 25, 2006)

All DPSS lasers (like the green you have) are sensitive to temperature variations, some more than others - it's part of their personality you might say.

Last year I was outside, taking some beamshots from a couple of green lasers, on a cold, foggy night (about 0C). In this temperature, a 25mW was noticeably brighter than an 80mW; the latter clearly more affected by the cold. As soon as they were back to room temperature inside, the 80mW performed normally again, being much brighter than the 25mW.

Probably not much to do in your case, apart from what you have already done - except get another laser and hope it's less sensitive to the cold; bit of a lottery really..

Regards,
Erling


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## brucepeter2002 (Apr 25, 2006)

Many thanks for the reply - Seems I have got a bad one that needs a heater. As this was a birthday present from the wife I have to "control" my feelings.
After I had the problem I took it apart (yes it still worked when I got it back) and I was fascinated with with it - although I did not expect to work on it with a watchmakers eyeglass - Next step will be to strip it down again and try some freezer spray on some of the (few) components to see if the problem is on the board - next I will try the laser tails with a very quick blip on the spray to see if it dims - I can only hope its a board component.
Any pointers (forgive the pun) - I have nothing to lose as its no good as it is...
Will just have to work in the dark so the wife dont know what Im up to.
Peter


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## brucepeter2002 (Apr 25, 2006)

Hi all.

Messed round with the freezer can and as soon as you hit the brass case the light level reduces.
Seems that I have to forget using this one and will have to consider another.
*Next question* - What make would you recommend I look for because the published output on Ebay makes me laugh - I need a good beam which is only used sensibly and with caution to place over a star with no Joe public or other astronomers around to cause problems to.
As I caught a cold the last time round (just unlucky) I think you chaps out there have far more knowledge than me so any help you can give me to point (trying) me in the right direction would be well received.
Thanking you in advance.
Peter


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## Tritium (Apr 25, 2006)

Lucky Duck is having a halfoff sale this week. Use the promotional code HALFOFF at checkout. Just picked up a Jasper Always for my 10" mead reflector.

www.luckyduck.com

Thurmond


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## brucepeter2002 (Apr 25, 2006)

Many thanks for the advice. I have placed my order and got the 50% so I would like to thank you for that as well. Just one other bit of advice I could do with - how do I explain to the wife her green laser birthday present has not only shrunk but also turned from a black case to a silver case... I can usually baffle her with science but I stand no chance here - a designer fitted case would just not work for a mature male - any other ideas.
Joking aside - many thanks for your help and I will let you all know how I get on - incidently you can see my Meade telescope and the gear I have at www.peterbruce.pwp.blueyonder.co.uk if your interested.
Regards
Peter


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## jkaiser3000 (Apr 25, 2006)

I agree the problem is most likely the crystals getting too cold to work efficiently. I think your best bet would be to fashion some sort of heating blancket to prevent it from geting cold. you could keep it in your pocket until necesary also. From your description, sounds like you only need it for a couple of minutes while you align your scope.

You can check this web page, it has instructions for building a dew preventer that may be adapted for your needs. Or check Kendricks page for an already built one.

Think of it this way, another opportunity for a do-it-yourself project :rock:


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## brucepeter2002 (Apr 25, 2006)

Thanks for the info but I have all the gear if you look at my web site in depth. The problem with keep taking the laser on and off is of scope to finder alignment. Once aligned it would remain spot on so to remove it each time defeats the object as it would need to be realigned again. The laser I have works better when heated - put it on the heater (still like winter over here so heaters still on) and watch it go - but as it cools down the level falls off. - Time for a new one. - so ordered it...
I was considering a few wire resistors around the case under the insulation I installed but thats more wires going to the scope and with loads of leads already it just makes no sense. I can only hope the new 5mW unit will cut through the light pollution of my London suburbs and give me a target green spot to align to. Trouble with standard scope finders is that you end up in weird positions trying to look down them because they dont have a turnable diagonal. You have this on the main scope as standard but they insist you break your neck with the finder... The green laser on an adjustable mount was the anwser for me (fitted it neatly into an old red dot finder scope) - before buying the original unit I did consider the rifle type on Ebay but they come from Hong Kong and the seller has made the feedback "private" so thats a no go area for me. The rifle green dot laser is powered by a 123A cell which is a far better battery in the cold. I can only hope the new Jasper Always laser unit from Luckyduck works well as this is my last chance. It has been an expensive trip so far however the reward and fascination for the subject is as interesting as adaptive optics (no I cant afford that).
Regards
Peter


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## jkaiser3000 (Apr 25, 2006)

yep, using the finderscope can be a pain in the neck sometimes, quite literally :thumbsdow. Anyway, I find my 5mw can punch through my light pollution, which I expect would be similar to yours. so I don't forsee any problems for you in that respect. I believe my limiting magnitude to be around 2, 3 at best. I can't see polaris from my location, but that's mainly because it's hiding behind a montain :laughing:. It may rise above the mountain in the future, but I'm not holding my breath :lolsign:

clear skies


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## RadarGreg (Apr 25, 2006)

If it is getting that cold, it might be a problem with the batteries as well. Have you tried lithium cells? I have an AstroAimer from www.hotechusa.com, and it runs on CR123a cells. It also has red and white LEDs so you can read your star charts or save your night vision. It is a bit pricey, but well constructed. I don't use mine for astronomy, but more for tactical use. The barrel of the AstroAimer is the same size as most star finder mounts, so you don't need to go the duct tape/ home brew mount route. Good luck,


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## Athoul (Apr 26, 2006)

It's also not just the crystals that perform differently when cold. As the laser diode gets cold it will shift towards blue and when it gets hot will shift towards red. Now the crystals will lase optimally when pumped with 808nm radiation, so what this means is that as the diode gets colder it is now outputting at a lower frequency then 808nm, perhaps 804nm(aproximation) this will result in less output from the ND:YVO4 crystal. Likewise when the diode gets to hot, it will start to shift further into the IR spectrum...again causing a reduction in output.

Now temperature also effects the crystal on the atomic level, so this will also have an effect on output... anyway without going into a huge explanation, basically it's a combination of all these things that result in decreased output with temperature changes.


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## brucepeter2002 (Apr 26, 2006)

Its interesting to note that the temp range of the device and the crystal operate within such a narrow range which would be unacceptable within most other electrical applications. I also note that the Luckduck advert provides some way around this with a circuit that controls the output power with a feed back system of control which is why I felt the operating range would be broader and thus be better suited for the scope. If this new unit fails my only option is to warm the unit with a few wire wound resistors which would not be an ideal situation because this scope is used at our caravan (*see my web site above*).
Green laser pointers waving about all over the sky can be a nightmare at any astronomical gathering because you can kiss goodbye to any imaging you are doing as the beam passes over the object your trying to image which is why I wanted the laser mounted and aligned with the scope so I can just fire it up to do my initial star alignment and cause no problems to man or beast. I must admit that I will take a short exposure of the projected laser "star" to see what it looks like as it will be an interesting exercise to see how the beam will spread after a few thousand feet of projection. I use a Starlight Xpress MX7C colour camera which is very sensitive and has a Peltier cooled Sony super HAD CCD chip and this will show up any photon you hit it with...
Regards
Peter


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## EGP (Apr 26, 2006)

Peter, had a brief look at your homepage yesterday. Must say your Jupiter shots look amazing, considering they're taken with amateur equipment  

Since your wife probably isn't looking here, could you give a hint at what the cost of the involved equipment has been ?  - I take it a 10" Meade doesn't exactly come cheap...

Regards,
Erling


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## comozo (Apr 26, 2006)

Like Athoul said there is an optimum operating temp for the MCA and diode which in this case starts around 70F - ends about 90F.


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## bg2vo (Apr 26, 2006)

Some LP work well at low temperature and some are not. You're just unlucky.
I've tested dozens of lasers against temperature variation.


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## SuperNinja (Apr 26, 2006)

brucepeter2002 said:


> The rifle green dot laser is powered by a 123A cell which is a far better battery in the cold. I can only hope the new Jasper Always laser unit from Luckyduck works well as this is my last chance.


Yeah, thats what Luckyduck says on their site.



Luckyduck website said:


> *Cold Weather Battery*
> Green lasers are great for astronomy, but did you know ordinary AAA-batteries lose most of their strength when the weather gets cool — even below 60°? That’s why the Jasper Always works on a special 3 volt lithium battery that can handle cooler temperatures. Ideal for astronomy and other outdoor uses, the Jasper Always retains it’s strength even on chilly nights.


http://www.luckyduck.com/lasers/now.php


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