Laser Centre Finder / Edge Finder

I treated myself to one of these last week, but I'm not "getting it".
From the web materials, I expected it to produce one very small red dot, ie
about 0.05mm ish. What I actually got when I switched it on was quite a large "splodge" which was made up of some laser sparkle and what appeared to be about five small red dots. Pointing at a matt black finish made the five dots pretty clear. I called the supplier to see if this was a colimation problem and they volunteered to check one from stock and send that out pdq, which they did. Just tried the "checked" one and it's the same as the first.
So not at all sure whats going on here, do I need new eyes?
Steve
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rittercnc.com had written this in response to http://www.polytechforum.com/modelengineering/laser-centre-finder-edge-finder-4237-.htm :
Steve wrote:

The five dots that you see are so called laser "modes". They are unavoidable - laws of physics at work. They could, however made the laser diod's opening smaller - just big enough to pass a single mode - to make the dot smaller at the expense of greatly lowering the brightness. I guess, they didn't. I don't believe you can do anything about the size of the dot then.
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wrote:

         You will get a much more sharply defined pinpoint if you add the optional polarizing attachment - see http://www.chronos.ltd.uk/cgi-local/ss000001.pl?RANDOM=NETQUOTEVAR%3ARANDOM&PAGE=SEARCH&SS=laser+centre+finder&TB=A&GB=A&ACTION=Search
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On Fri, 23 May 2008 18:29:41 +0100, Chris Edwards

With most simple laser pointers, at short range, the image is so bright that the eye saturates on the central spot. This makes the spot appear much larger than the main high intensity point.
The usual way of dealing with is a neutral density light attenuating filter or crossed polaroids between the pointer and the target. Crossed polaroids have the advantage that the brightness can be adjusted by changing the relative rotation between the two polarising films.
This is just a matter of brightness attenuation. It really doesn't matter where the attenuation is placed - between the laser and the target, or between the target and the eye.
If you've got an old pair of polarising sunglasses the two halves can be crossed at a suitable angle to give exactly the same effect.
Jim
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Thanks Jim. I have some lenses in the scrap box somewhere! One other effect that I didn't appreciate was the appearance of "columns" of light in the laser spot. The columns don't go away when you attenuate the light, though the spot does reduce in apparent size. Still not confident that a piece of ground silver steel and a cigarette paper stuck to the workpiece isn't more accurate for edgefinding though.
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Make your own using a 632 nM frequency. I think all these cheap ones use 650/660 which has way lower visibility.Yes, I think it should be a 'dot' that is 'focussable'.
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Answer from the manufacturer is you need the polariser with unit serial numbers greater than 7300, so the polariser isn't really an optional extra... The polariser is another 12 +VAT, so getting to be a very expensive piece of kit.
Steve
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Should have purchased direct from Skip, www.lasercenteredgefinder.com
There are UK bases commercial laser finders, but they really are expensive.
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treated myself to one of

Should have purchased direct from Skip, www.lasercenteredgefinder.com
There are UK bases commercial laser finders, but they really are expensive.
Last time I bought kit from the us, the ticket price was half the UK price. By the time customs and excise had done with me, it cost me more than the UK price!
Probably a gamble in the buyers favour though.
I did swap notes with Skip over the weekend and he is very customer service oriented - full marks -
Steve
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