Oh damn... Now i'm curious. Are you on a promise or somethingOriginally Posted by stanwax
Maybe I could - though I guess I wont be doing much scanner tuning this weekend
Rob
Jem
Senior Member
Oh damn... Now i'm curious. Are you on a promise or somethingMaybe I could - though I guess I wont be doing much scanner tuning this weekend
Rob
Jem
Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.”... Douglas Adams 1952 - 2001
hehehe I guess in reality I am!Oh damn... Now i'm curious. Are you on a promise or something
Jem
Rob
If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
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Laserists do it by the nanometre.
Stanwax Laser is a Corporate Member of Ilda
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www.photoniccleaning.co.uk
Senior Member
Keeperx
When I talk about PPS, it is the position instructions per second that I am referring to and understand that 20k scanners scan a circle faster than the ILDA TP which explains why the circle scans without flicker unlike the test pattern.
Yours and everyone else's input on this issue is appreciated. My reason for my question was really for curiosity.
Jem
You know what they say about what curiosity did to the cat.
Rob
I meant the next time we meet for laser related reasons.
With out having the means to check the PPS rate of the PM25 my self I think I should take George's word on this as gospel.
Carl
Senior Member
rob said
aahhhhhhhehehe I guess in reality I am!
so you off to the fetish weekend again then rob....
all the best ... Karl
Senior Member
Karl, Do you know something about Rob that the rest of us should know about?
Carl
Karl you tawt - my spelling is getting worse
I have just wet myself laughing at that - reminds me I must put talc on the shopping list
Rob
If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
-----------------------------------------------------------------------------------------------
Laserists do it by the nanometre.
Stanwax Laser is a Corporate Member of Ilda
Stanwax Laser main distributor of First Contact in UK - like us on Facebook http://www.facebook.com/FirstContactPolymerCleaner
www.photoniccleaning.co.uk
Senior Member
Carl said
yep .... i know that he does not have many good photos of himself on the internet tha can be photoshopped into other photos ...Karl, Do you know something about Rob that the rest of us should know about?
rob can you post a decent facial shot in your foto albums that i can use ....
did i just say Facial shot .... oooohhh errrrrrrr misus
Rob .... at least when you wet yourself ... no one knew ...... you just had a warm sensation in the rubber outfit
all the best .... Karl
This is not true at all. A sine wave at 20,000 hertz would be impossible for even 30K scanners to handle. The maximum *small step* bandwith of a 30K scanner is around 2500 Hz.
Those "points" in the point per second speed have limits on how far they can be from one another. In the case of the ILDA test pattern, the central circle is actually a series of 12 points forming a dodecagon where all 12 of the points are outside of the center square. (Actually it's 36 points, because the figure is traced 3 times in a row.) The scanners, of course, never get close to these points. That's why you see the image as a circle that lies completely within the square. Still, one trip around the circle represents 1 cycle (up and down, or left and right).
If you consider that when drawing the circle, the scanners are ballistic (that is, under constant, maximum acceleration the entire time, because they never reach their destination points), then you can see that it's fairly easy to calculate the maximum speed (in Hz) of the scanners. Assume that all you scan is the center circle. So that's 12 points for a single cycle. If you're running 30,000 points per second, divide by 12 points in the frame, and you'll see that you'll make 2500 trips around the circle in a second. Thus, the small signal bandwidth is 2500 Hz.
Of course, this ignores the fact that there is significant distortion between the 12 points in the ILDA file and the resulting scanned circle. So in reality the bandwidth is even lower than that. But it's a good starting point.
Bottom line: a 20Khz sine wave is an order of magnitude too fast for today's scanners.
No, it couldn't. When the scanners are scanning the circle in the ILDA test pattern, they are already moving as fast as they can. You aren't going to get any more speed out of a set of scanners once you tune them (correctly) to the ILDA test pattern. Also you don't "reduce" the scan speed when you tune to the ILDA pattern. You tune at the speed you will run at.a CIRCLE could be scanned much faster than the ILDA pattern
There is a lot of good information about the ILDA test pattern on the Pangolin website, and some more over at the old LaserFX website. You might want to read up on the reasons behind the specific portions of the pattern.
As for testing the speed of Carl's laser bench, he's going to need an Oscilloscope to test it. And his reasoning is sound. If you tune at a high speed and then display at a lower speed you will get overshoot. In extreme cases the center circle of the ILDA test pattern will enlarge to the point where the scanners actually manage to reach the outer points of that dodecagon!
The opposite is just as bad - tuning to a slow speed and then displaying at a higher one causes undershoot. The scanners never reach *any* of the points in the image. Both of these cases are bad for the quality of your scanned image.
Adam
When we had a go at tuning Carls scanners (before he did some rewiring that affected the output considerably) I played the ilda tp through Mamba set to 18k. Carls concern now is that the PM25 is putting out the said 18k and I guess thats what he needs confirming. When he nexts visits me - dont worry Carl for casual visitors I pack the rubber away - I will be able to examine the board output with a scope and with a bit of luck compare it to a signal from Mamba, set to 18k, of the same frame.
Rob
If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
-----------------------------------------------------------------------------------------------
Laserists do it by the nanometre.
Stanwax Laser is a Corporate Member of Ilda
Stanwax Laser main distributor of First Contact in UK - like us on Facebook http://www.facebook.com/FirstContactPolymerCleaner
www.photoniccleaning.co.uk
Rob;
If you're good with your scope, then load the ILDA test pattern on Mamba and look for the center circle in the pattern on your scope. It's about 2/3 of the way through the waveform. (It will be visible on both the X and Y traces, so it doesn't matter which one you connect the scope to.)
Keep drilling down until you find it. (It will be 36 points clustered together that create a rough sine wave that is 3 cycles long.) Remember that the amplitude will be rather small compared to the rest of the signal.
Measure the time between peaks there just to confirm that Mamba is running at the correct speed. (And so you're familar with what it looks like so you can find it again.) Then load the ILDA test pattern on the bench and do the same. You'll know right away if the speed is off!
Easy, Peasy, Lemon Squeezy!
We did this at FLEM a long time ago. Bill Benner was trying to explain what sample jitter was, and some of us (Buffo sheepishly raises his hand) couldn't quite visualize what was going on, so Bill fired up my 'scope and zoomed in on the waveform coming out of Fred's Easylase USB DAC. And sure as hell, you could see the timing shift back and forth!
Adam
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