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Posted by Steve on May 23, 2008, 9:54 am
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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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Posted by rittercnc.com on May 23, 2008, 12:50 pm
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rittercnc.com had written this in response to
http://www.www.rittercnc.com/modelengineering/Laser-Centre-Finder-Edge-Finder-4237-.htm
:
Steve wrote:
> 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
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.
This is ma' sig
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Posted by Chris Edwards on May 23, 2008, 1:29 pm
Please log in for more thread options wrote:
>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
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
--
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"
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Posted by on May 24, 2008, 5:07 am
Please log in for more thread options On Fri, 23 May 2008 18:29:41 +0100, Chris Edwards
>wrote:
>
>>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
>
> 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
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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Posted by Steve on May 24, 2008, 8:52 am
Please log in for more thread options
> On Fri, 23 May 2008 18:29:41 +0100, Chris Edwards
>
>>On Fri, 23 May 2008 14:54:15 +0100, "Steve"
>>wrote:
>>
>>>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
>>
>> 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
>
>
> 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
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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> it".