DX 50 review

Yesterday I received my DealExtreme "True Wish" 50mW. At $25.45 it's a quarter of the price as a quality WL/etc laser.

(I'll highlight the some keywords that summarize the laser)

I must say I have never been this happy with any laser buy! (technically my only other "buys" are 5mW'ies if you don't count buying a DVD burner for the sole purpose of extracting the diode, twice)

The gift box is plain suede and the foam inside smells.




The manual is in Chinese Engrish, and shows how to put in the batteries, it should not be operated outside the temperature range 20[sup]o[/sup]C to 35[sup]o[/sup]C, it has a warmup period of less than 5 minutes (strange fact!?) and a lot of warnings.

It came with two Alkaline AAA batteries, which were not new and already somewhat drained. (measured 1.3V open loop)

The laser seems to work well on 1.2V NiMH batteries. In fact I strongly recommend 1.2V NiMH batteries because even with those, the laser heats up significantly (36[sup]o[/sup]C after 15 min continuously at 22[sup]o[/sup]C room temperature) and it saves the environment and your wallet.

The beam exits off-center (I heard this a lot about this laser) but it's 1.2x1mm oval with a nearly gaussian profile. It also seems to have a soft-on built into the circuit as it takes about 0.5 seconds to go from 0 to the level at which it stabilizes (doesn't matter if it's a cold or warm start). Divergence is 0.579 mRad.

It seems to have a warmup period alright, and with it some unwritten manual rules (which I will write down now). Sometimes when the laser is powered on when cold, it will peak at a certain intensity and stay that way. When it's on for like 10 seconds and you turn it off and on immediately, the power will be more than doubled!

I don't have a power meter but the spot is clearly visible under a bright sun. I can make yellow with my red ~230mW at approx 1/3.5th power. I guess between 50 and 80mW red corresponds to this one. (Still using NiMH batteries)
On my infrared thermometer (mini thermopile) it shows not much response, about 1/5th of that of my red ~230mW at full power. This would suggest there is an IR filter present.

What? 0.579mRad? Isn't that like, really good?

Yep. Do the math if you don't believe me. 10 meters, 1.2mm -> 7mm (+- 10%)
Lucky pick, I guess

Yeah, I was wondering about that mRad too. That's insanely good for such a cheap pointer.

Maybe you got a 'defective' one (where the defect is amazing divergence).

I forgot to say, it can't light matches, even with external optics. It will only smoke a little.

Zom-B said:

It seems to have a warmup period alright, and with it some unwritten manual rules (which I will write down now). Sometimes when the laser is powered on when cold, it will peak at a certain intensity and stay that way. When it's on for like 10 seconds and you turn it off and on immediately, the power will be more than doubled!

Click to expand...

Such issues are typical of these lasers i guess. Perhaps it has something to do with contact resistances, only current measurements can shine some light on that.

Nice review.

Benm said:

[quote author=Zom-B link=1210168161/0#0 date=1210168161]
It seems to have a warmup period alright, and with it some unwritten manual rules (which I will write down now). Sometimes when the laser is powered on when cold, it will peak at a certain intensity and stay that way. When it's on for like 10 seconds and you turn it off and on immediately, the power will be more than doubled!

Click to expand...

Such issues are typical of these lasers i guess. Perhaps it has something to do with contact resistances, only current measurements can shine some light on that.
[/quote]
I'll get back to that after school. All I can say now is that it thresholds at 180mA and drains 300mA at full capacity. (900mW in 50mW out efficiency=5.6%)

I'll also add yet another rule. When you leave it on for more thatn a minute, the power will eventually make a jump to double power.

No totally a warmup issue. When cold and I reach 225mA it's bright. When I increase to 230mA it jumps to a dimmer state. When I keep increasing current, the intensity increases less but when I decrease the current it immediately becomes dim until it jumps to the brighter state below 230mA. All this has to be done in less than 5 seconds to prevent warming up.

When warmed up, the intensity keeps increasing gradually between 180 and 300mA, as expected.

Zom-B said:

Yesterday I received my DealExtreme "True Wish" 50mW. At $25.45 it's a quarter of the price as a quality WL/etc laser.

Click to expand...

true 50mW is $54.50, the regular [probably not]50mW is $25.45

I just received Alpha125's/xarylx' power meter, and the laser emits 37mW peak at exactly 3.00 Volts, and 42mW peak with two NiMH batteries.

Those are pretty decent peak values. I'm still bothered by the unpredictable power output of these lasers though, they all seem to have thermal issues one way or another. You are lucky to have on that likes heat though... the slow powerup can be annoying, but to me much less than the reverse effect where it starts dimming badly within a minute.

Zom-B said:

Yep. Do the math if you don't believe me. 10 meters, 1.2mm -> 7mm (+- 10%)
Lucky pick, I guess

Click to expand...

I don't get it.

The equation giving the diameter(D) in centimeters depending to distance(X) in meters is:
D = 0.12 + X· 200·Tan(0.0002895)

So for X = 10 m then D is indeed 0.699 cm ~= 0.7 cm like original poster said.
But for X = 1000 m then D = 58 cm !!

So the diameter of the beam after 1 kilometer becomes around half a meter!!!! But i have seen countless very cheap 50/30/10/5 mW green lasers where they point to a mountain or a building 1-2 or even 3 kilometers away and the beam, the dot of the beam looks very small, tiny, and definitely not half a meter!

So what is going on??

It depends on which end of the beam you are when estimating the
diameter of your beam (optical illusion if your holding the laser).. IMO

Jerry

If the laser beam has a divergence of ~0.6 mrad, then the dot will appear under an angle of 0.6 mrad to the one holding the laser (except for small distances, since the beam already has a certain diameter when emerging from the lens - effectively it will be coming from a point source 2 or 3 meters behind you). In more familiar terms, that's about 1/30 of a degree, or 2 minutes of arc, or 1/15 of the diameter of the full moon (which is a lot smaller than most people think it is), or about twice the diameter of venus when it's at its brightest - effectively, a fat dot, something that is just barely not a point if you've got 20/20 vision.

the laser int he photo seems not to be so shining.......it seems a 5mw......