Discussion
www.kustomsignals.com/dw/prolaser.asp
john57 said:All Lidar units are being questioned, they all work on the same principle (modified rangefinder, can be fooled). The LTI is under particular scrutiny simply because (I believe) it's the most commonly used product.
Pro Laser ...... probably the Pro Laser III - is very accurate.... not to be confused with an LTi 20/20 which is the one that has been questioned recently. The beam on a pro laser is very, very narrow - even at long distances.
gooby said:
I am talking "theory"
The only verticle area on my car is the number plate. My laser detector detected the signal and is tucked up on the rear view mirror.
What is the chances of having "slip" in this case?
IMO this would depend on the beam width at your car (this being a function of beam divergence, tail-off at beam edge and range from the Lidar gun). Chances are that a portion of the beam hit your VRM, this being the first (and the strongest) source of reflection, the Lidar gun will measure the time-of-flight to that first surface, even though the beam will strike/reflect from other surfaces. If the beam hit the VRM at any time, there is no chance of achieving an undetectable sweep error (change of reflection co-efficient would be far too great, hence no false speeds displayed).
It’s likely that a portion of the beam will bounce off the bonnet above the VRM onto your detector so activating it; hence don’t assume your VRM wasn’t correctly hit if your detector activated, irrespective of operated range.
However, if the beam didn’t strike the VRM at all (there’s no way to know, the misalignment process has a flaw – ‘parallax misalignment’, assuming it was done in the first place), and the beam was panned – probably! This was successfully demonstrated with an American LTI at an American court.
Short answer – It’s possible!
smeggy said:
What is the chances of having "slip" in this case?
Short answer – It’s possible!
Agreed. They are heading for big trouble with laser speed meters.
The fundamental problem is that slip error can appear at any time and cannot be detected by the electronics. This means that no laser speed meter reading is 'beyond a reasonable doubt' and therefore no convictions are safe.
I was going to post regarding this very subject just last night, but forgot all about it, so here it comes.
The Good Cpt Sideways does i believe own one of these guns, so if he's reading, id like to make a suggestion.
Take the laser gun and aim it upon a patch of wall thats painted white, so as to give a good reflection preferably from a nice 10/20/30 feet away, whatever, just so long as its a known distance- the reason for this will be revealed in a bit.
Then get a friend to observe the "beam" as it impinges upon the wall using either a night vision scope or b/w security camera and make a note of the size/diameter of the beam.
The reason we wanna know the beam size is so we can tell what diameter the beam will ACTUALLY be at further distances using math.
Its often said to be "about" (thats scamera speak for -we dont know-or care) 3 feet at 1000 feet distance.
For all we know the actual beam size may be 100 feet diameter and we'd never know would we?
For those who dont see the significance in the beam diameter, let me elaborate; What else can a wide diameter beam be measuring besides YOU hmmmm?????
Exactly.
The Good Cpt Sideways does i believe own one of these guns, so if he's reading, id like to make a suggestion.
Take the laser gun and aim it upon a patch of wall thats painted white, so as to give a good reflection preferably from a nice 10/20/30 feet away, whatever, just so long as its a known distance- the reason for this will be revealed in a bit.
Then get a friend to observe the "beam" as it impinges upon the wall using either a night vision scope or b/w security camera and make a note of the size/diameter of the beam.
The reason we wanna know the beam size is so we can tell what diameter the beam will ACTUALLY be at further distances using math.
Its often said to be "about" (thats scamera speak for -we dont know-or care) 3 feet at 1000 feet distance.
For all we know the actual beam size may be 100 feet diameter and we'd never know would we?
For those who dont see the significance in the beam diameter, let me elaborate; What else can a wide diameter beam be measuring besides YOU hmmmm?????
Exactly.
deltafox said:
Take the laser gun and aim it upon a patch of wall thats painted white, so as to give a good reflection preferably from a nice 10/20/30 feet away, whatever, just so long as its a known distance- the reason for this will be revealed in a bit.
Then get a friend to observe the "beam" as it impinges upon the wall using either a night vision scope or b/w security camera and make a note of the size/diameter of the beam.
………
For all we know the actual beam size may be 100 feet diameter and we'd never know would we?
For those who dont see the significance in the beam diameter, let me elaborate; What else can a wide diameter beam be measuring besides YOU hmmmm?????
You might be right about the divergence (it has even been alledged that there are in fact 3 beams); unfortunately, the method of measurement isn’t as simple as that.
The output pulse durations of Lidar are short, very very short, so short that the maximum average power output is up to 50uW, that’s less than a typical IR remote control (even thought the laser power rating is ~30 watts).
Worse still, aiming the LTI at a highly reflective surface will cause the unit to compensate such that it’s own (highly sensitive and fast) receiver won’t saturate, hence substantially reducing the output power. Therefore I doubt that any camera or NVG will detect anything at all in the described set-up, even if done in total darkness.
(by all means try)
A better method may be to aim the LTI such that there will be a minute (and constant level of) reflection (to cause the gun to operate at full power) and pan across the beam (or pan the beam across the camera) whilst the camera is pointed directly at the gun; hopefully it’ll capture the flash at the Tx aperture. This method is more involved, but it should work.
There is also the issue of the rate of tail-off at the edges of the beam, it's likely to be a gradual decrease, so where do you take the cut-off level to be: 50%? 10%? 1%?
I have seen a small dot at 5m range using an IR Filter & a Digi SLR camera, it was very very faint even at that range though.
I think you could do it with a digital video camera & telephoto lens. Ie fix the gun position & move the receiving camera to see the projection.
Though there is an easier way.... SLD 920's are rather sensitive
from 100ft+ range the SLD's detect the beam when aimed at approxiamtely 1m either side of the receiving/emitting heads. A spare set is available for testing purposes if anyone has a spare afternoon & some patience & a measuring tape.
My guess is at 500ft it's 1-2 cars wide
I think you could do it with a digital video camera & telephoto lens. Ie fix the gun position & move the receiving camera to see the projection.
Though there is an easier way.... SLD 920's are rather sensitive
from 100ft+ range the SLD's detect the beam when aimed at approxiamtely 1m either side of the receiving/emitting heads. A spare set is available for testing purposes if anyone has a spare afternoon & some patience & a measuring tape. My guess is at 500ft it's 1-2 cars wide
cptsideways said:
I have seen a small dot at 5m range using an IR Filter & a Digi SLR camera, it was very very faint even at that range though.
I think you could do it with a digital video camera & telephoto lens. Ie fix the gun position & move the receiving camera to see the projection.
Though there is an easier way.... SLD 920's are rather sensitive
My guess is at 500ft it's 1-2 cars wide
Significantly wider than "pinpoint" as they always like to portray it then!
NASA's next mission to Venus will map the surface using LIDAR. It will orbit at an average altitude of 800 miles and the mapping 'footprint' of the LIDAR will be about 25 miles wide, giving a beam divergence of about 3%.
If this same divergence applies to a laser speed-gun, then the beam will be about 3m wide per 100m - about the size of a Renault Clio...not exactly death-ray stuff, is it?
By the way, you can capture IR laser images on a CCD movie camera - I know, I've done it.
If this same divergence applies to a laser speed-gun, then the beam will be about 3m wide per 100m - about the size of a Renault Clio...not exactly death-ray stuff, is it?
By the way, you can capture IR laser images on a CCD movie camera - I know, I've done it.
MGBGT said:How do you think SPECS and ANPR works?
By the way, you can capture IR laser images on a CCD movie camera - I know, I've done it.
Captain,
I just realised how you can very easily get a much better response. Add an attenuating filter or partially cover the Rx apeture (I believe that to be the bottom lens). The LTI will compensate for the weak signal at the receiver by boosting the power output - all the better for your camera to capture.
I can supply zoom video cameras without the usual IR blocking filter if necessary.
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