Laser pointers

ChrisJefferies

Hi Folks,

I'm thinking of getting a laser pointer to help show my son what I'm talking about when we look up at the night sky.

Ebay have a load of 1mW type devices, some of them very cheap. Is 1mW powerful enough to highlight stars or do I need to invest in something stronger?

Thanks

Chris Jefferies

slade_x

ChrisJefferies wrote: »

Hi Folks,

I'm thinking of getting a laser pointer to help show my son what I'm talking about when we look up at the night sky.

Ebay have a load of 1mW type devices, some of them very cheap. Is 1mW powerful enough to highlight stars or do I need to invest in something stronger?

Thanks

Chris Jefferies

No 1mW from ebay will not be enough unless you plan on pointing out stars on a star chart a couple of feet in front of you. in that power range the mainstream lasers will be very disappointing.

the specification of most pointers easily available are highly exaggerated. a really good laser than can sustain its rated output be it 5, 20, 50 to 100mw will be very expensive. 20mw Astronomical pointers roughly start at $100 and are green in colour due to the high visibility of light scattered in that wavelength, for your purpose you would get away with one of the much cheaper ones

I purchased one for myself a couple of years ago from dealextreme cheap enough, im not certain if its the exact same range but the following appear very similar:

http://www.dealextreme.com/details.dx/sku.1372 100mw
http://www.dealextreme.com/details.dx/sku.1998 150mw

The expensive high rated lasers that can sustain their rated output actually double as slow cutting lasers. You do not want one of these. they are extremely bright and goggles are recommended with their usage especially to filter unwanted infrared light. i feel they are also overkill for the intended purpose. a higher rated laser will go further and illuminate brighter naturally but im sure budget is important

Having that said if the linked lasers are similar to the one i purchased for the same purpose as you, they will also be very bright. And i would always recommended extreme care be taken when any laser is being used. considering the intensity even with the cheaper model i would recommend goggles especially indoors as you will no doubt play with it also. no one would however blame you. they are a very novel device.

One bit of warning though its possible irreversable eye damage can occur from indirect (yes indirect) exposure to one of these lasers. Obviously direct exposure damage is almost guaranteed. the cheaper ones are not filtered from infrared but may only produce negligable amounts or none at all at low power (there's also a chance you could come across an inexpensive good quality laser that might not have an infrared filter).

I wouldnt even trust a teenager with one. having that said i dont even think i would trust some of my friends with one who are very much in their late twenties.

I cant stress enough how potentially dangerous these laser pointers are. undetectable accumulative eye damage is not of preference to anyone especially an observer of the night sky

There are user videos posted on the site i linked to but in the following link from the site, the beam intensity i think you can expect from the above lasers is accurate http://www.dealextreme.com/feedbacks/browseVideos.dx/sku.1372~id.7098

It is likely you could find a similar "cheap" laser on ebay, but i dont really trust the majority of sellers on ebay in their claims

ChrisJefferies

Thanks slade_x.

I'll give it some thought and see if I still want to buy one. I'm concerned that they might not be such a good thing to have around children, even when I follow all the safety measures.

ednwireland

errrm i picked up a 1mw a few weeks (green) and its fine for pointing to stars cost about a tenner took weeks to come from china - lets be honest at that price what have you
i was suprised myself - i went for one with AAA batteries as its easier to get replacements

thecornflake

Don't quote me on this as i am not a judge or anything but , i think there is only a certain wavelenght of laser legal in Ireland ~630nm i think.
This would mean green is illegal and i also think there is a limit on the Watts also.
However i haven't really heard of it being enforced.

Calibos

ednwireland wrote: »

errrm i picked up a 1mw a few weeks (green) and its fine for pointing to stars cost about a tenner took weeks to come from china - lets be honest at that price what have you
i was suprised myself - i went for one with AAA batteries as its easier to get replacements

The problem with the cheap chinese lasers is that one can't be gauranteed they have proper IR filtration. Thats what does the damage.

100 euro gets you a good 10mw one for astronomical use although greater than 5mw is banned in most countrys. To be sure you are staying within the law and getting a good quality unit its probably safer to pny up the extra euros and get a GLP from an actual online astro shop as opposed to a chinese ebay seller.

Popoutman

I've purchased two of the HongKong Specials over the past 3 months.
Both were advertised as 5mW 532nm green laser pointers, 2x AAA batteries required.
One was just bright enough to give a green beam at night.
The other was bright enough to easily give a green beam that I could just follow in twilight, and it would illuminate a building 2km away.
As long as you aren't looking into the beam, it'll be fine.
Class IIIa recommend not looking into the beam anyway.

Go with a €5 pointer - you may get lucky.

ChrisJefferies

As they're so cheap on ebay I'll give one a try and see how I get on. Probably not the right time of the year to be buying one now but there you go...

Thanks for the help.

Calibos

OP asks on Astronomy forum what laser should he get to point out stars to his kids
........
Amatuer Astronomers on said Astronomy forum tell him he needs a 5mw to see the beam at night and not to buy dirt cheap GLP's on Ebay, because they break easily and are very possibly dangerous with no IR filtration
.........
OP says thanks and will be picking up a cheap €5 laser from ebay shortly.

:rolleyes:

Popoutman. Believe me when I say there is nothing that irritates me more than reactionary hysterical anti GLP scare stories posted on astronomy forums. However, while the danger with a good GLP might only come from directly looking at the beam, the problem with the cheap lasers with little or no IR filtration is that the dangerous IR radiation is invisible and the IR does not come out of the GLP lense in a tight beam like the visible frequencies. It comes out in a much wider cone. So you don't even have to be looking directly down the barrel of the laser to be getting dangerous levels of IR in the eyeball.

FISMA

Chris,
A good strong flashlight is all you need. Even better, have you ever seen one of the hand held lights that the lads use for lamping? They are all you need.

Even on a clear night there will be enough of a beam to point out whatever stars you need to see.

John mac

I use a led lenser.

Abelloid

I had a 25mw Wicked Laser, it was very easy to see, even in strong ambient lighting. A little more expensive, but worth it IMHO.

Calibos

JustinOval wrote: »

I had a 25mw Wicked Laser, it was very easy to see, even in strong ambient lighting. A little more expensive, but worth it IMHO.

Thats where I got mine but didn't mention it in case it was against forum rules or something. I got the cheapest 10mw one they do. No need for anything more powerful.

Popoutman

I've just checked both of my GLPs with a few different IR sensitive cameras.
Off-axis, I'm not seeing anything brighter than the IR radiation from a tv remote control On axis? I'm not willing to illuminate the chips with the laser light, same as I'm nor willing to illuminate my retinas in the same way!

I don't doubt that there can be some really cheaply made items that are missing the relevant IR filter, and that if the IR radiation is slightly more divergent in such a case.

However for both of my pointers it's a non-issue - there's very little if any IR coming off-axis.

Calibos wrote: »

the problem with the cheap lasers with little or no IR filtration is that the dangerous IR radiation is invisible and the IR does not come out of the GLP lense in a tight beam like the visible frequencies. It comes out in a much wider cone. So you don't even have to be looking directly down the barrel of the laser to be getting dangerous levels of IR in the eyeball.

Gavinal

High powerful laser pointers maybe hurt airplane and also hurt your son without correctly method, my neighbor bought 200MW green laser pointer last month and his eyes was hurt by laser, so be careful!

you'd better choose lower-powerful laser pointers and good for your son.:cool:

Popoutman

Here's an interesting link:

http://www.nist.gov/customcf/get_pdf.cfm?pub_id=906138

PDF with a niec little simple test to see if your laser pointer is putting a lot of IR into the actual on-axis beam itself.