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Thread: Test Pattern Question

  1. #1

    Default Test Pattern Question

    Notice the double lines, what is causing that?

    I can't seem to get a good picture of the standard ILDA test pattern. It looks OK, flickers even at 30k but I guess thats normal. All my pictures are missing some of it although in real life its all there. Tried longer exposure on my camera but that didn't work either

    Circle touching the square and the "color" shift lines at the top look good but this pattern in that picture is the only thing I can find wrong in any of the patterns.


    Click image for larger version. 

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  2. #2
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    This is the Laser Media test pattern. What you're seeing is the fact that the test pattern is exposing a slight flaw in the tuning of your scanners. When those 2 lines don't touch, it means one scanner is running faster than the other. Not by much, though. With some additional fine tuning, you should be able to get that cleaned up. I typically flip back and forth between the ILDA test pattern and this one when tuning.

    Quote Originally Posted by demolish50 View Post
    Notice the double lines, what is causing that?

    I can't seem to get a good picture of the standard ILDA test pattern. It looks OK, flickers even at 30k but I guess thats normal. All my pictures are missing some of it although in real life its all there. Tried longer exposure on my camera but that didn't work either

    Circle touching the square and the "color" shift lines at the top look good but this pattern in that picture is the only thing I can find wrong in any of the patterns.


    Click image for larger version. 

Name:	double.jpg 
Views:	49 
Size:	1.55 MB 
ID:	43493

  3. #3

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    Is that also what causes O's to look like q when there are lots of O's being drawn? I thought it my scan angle but it makes no difference what angel I used.

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    I doubt it, but would probably need to see the frame to make a better guess. The tuning is pretty close, only slightly off from what I can see with the LM test pattern, and if you say the ilda test pattern also looks good then it may just be an issue with the frame itself.

  5. #5
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    Locate the low frequency damping and servo gain potentiometers on your scanner amps. Load the LM test pattern at a medium angle. Pick one amp and give each pot a fraction of a turn, say no more then one turn in either direction. Start with the damping, for it is more sensitive then the servo gain. See if gap between the lines expands or collapses. On one axis it should expand and on the other it should contract. You can then split the difference as needed between the two amps. If your amp has 20 turn instead of 10 turn potentiometers, you may need two full turns, in which case you should mark the screw position with a paint pen or permanent marker. If your scanners have two different mirror sizes, the larger mirror will be inherently slower, which is something to keep in mind. If things are way out, it may take more then one or two turns, but usually at the stage shown in your picture, the tuning is very close. The controls interact, which is why I'm suggesting small turns at first.

    The LM test pattern is designed to show the difference in the velocity between the X and Y scanners, using the diagonal lines. It will also show how well the velocities and damping match at the corners, as the damping error grows, the corners show "overshoot".

    http://lasershowparts.com/files/Arti...20Tutorial.pdf

    http://www.laserfx.com/Backstage.Las...Scanning1.html

    The ILDA pattern is scanned at specific angles, in order to standardize the tuning between users, this chart from Pangolin Inc. helps find the angle:

    http://www.pangolin.com/userhelp/scanangles.htm

    Steve
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  6. #6

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    That is a wealth of info. Exactly what I was looking for. Thanks .

  7. #7

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    So I was able to use my wife's camera and get a good picture, long shutter speed and my hands tend to shake but turned out ok. It does appear the blue circle is slightly outside the square on the horizontal axis. I had not noticed this before. I made sure I had an 8 degree scan angle this time though.

    Click image for larger version. 

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    green wall really makes the colors look funny =p

  8. #8
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    Hey guys. It's been awhile since I've posted here. I accidently broke off one of my scanner mirrors. I glued it back on pretty good but now I need to retune the scanners. I am scared to death to do this but I guess it's time to learn how. My problem is that I can't find the test pattern with the circle inside the square. The one I find has the circle outside the square and it's not a perfect circle. Is it ok to use this one for retuning? I'm using Spag...ti software on a home built projector for personal use only. Thanks for your help.

  9. #9
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    Quote Originally Posted by 2tall View Post
    Hey guys. It's been awhile since I've posted here. I accidently broke off one of my scanner mirrors. I glued it back on pretty good but now I need to retune the scanners. I am scared to death to do this but I guess it's time to learn how. My problem is that I can't find the test pattern with the circle inside the square. The one I find has the circle outside the square and it's not a perfect circle. Is it ok to use this one for retuning? I'm using Spag...ti software on a home built projector for personal use only. Thanks for your help.


    You have the right test pattern. You are misreading the speed test portion of the pattern.
    Set your scan angle to about 8 degrees on the screen. Increase your point rate (PPS) till the circle just collapses into the Square. At this point you;ll see whats going on. All this does is measure your upper scan speed.

    Google Search for "Buffo's scanner tuning tutorial"

    Steve
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