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Thread: My scanner up and running with Alphalite pro

  1. #11
    Join Date
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    Default is that a chinese laser

    have you got a chinese laser in there ? just wonder if you had had any blanking issues with it ? still have'nt sorted my blanking problem out
    looks cool
    dave321

  2. #12
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    Default Re: is that a chinese laser

    Quote Originally Posted by dave321
    have you got a chinese laser in there ? just wonder if you had had any blanking issues with it ? still have'nt sorted my blanking problem out
    looks cool
    Yes it is. I have no problem with blaking. I do however have to have reverse blanking turned on in Alphalite software
    "Gravity its not just a good idea its the law"

  3. #13
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    Default

    I have the same type of green laser and I think it's a little slow on the blanking. If I run my projector at about 20K and faster the blanking begins to be a problem.
    You know, I have one simple request. And that is to have sharks with frickin' laser beams attached to their heads!

  4. #14
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    Default

    Quote Originally Posted by Groover
    I have the same type of green laser and I think it's a little slow on the blanking. If I run my projector at about 20K and faster the blanking begins to be a problem.
    The images above were done at 30k with no problem with blanking.
    "Gravity its not just a good idea its the law"

  5. #15
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    Default Blanking problem?

    Quote Originally Posted by Groover
    I have the same type of green laser and I think it's a little slow on the blanking. If I run my projector at about 20K and faster the blanking begins to be a problem.
    Groover;

    I have one of the cheap chinese DPSS lasers in my Alphalite projector. I believe it's the same laser that Fred is using, and thus it's probably the same one you have as well.

    What sort of blanking problems are you having? The only problem I've noticed with mine is a power fall-off if the blanking duty cycle gets up around 15% or so. (IE: You'd expect average power to be 85% with a 15% blanking duty cycle, but actual power output is only around 45%...) So the frame is scanned accurately, but it appears dimmer than it should.

    Is this the problem you're experiencing? (From your post, I thought you were talking about the laser not coming back on at all, or at least the re-light being delayed, once you tried to blank above 20kpps - causing "dead spots" in the frame...)

    I can run my projector at 50kpps, and the blanking is able to keep up without any problems. (Well, within the timing limitations of the Alphalite hardware itself, that is!) Now, every once in a great while I'll come across a frame that has "tails" in a few places when it's displayed at high scan rates, but I think that's more a function of the timing inconsistencies on the parallel port and not anything to do with the laser itself.

    Basically the issue I have is that when the laser is blanked rapidly, it comes back on at the right time, but doesn't instantly come back on at full power. It starts at some lower power level and then takes a tiny amount of extra time (I'm guessing ~ 100 microseconds) to ramp back up. But if the blanking duty cycle is high enough, the laser never gets all the way back to full power before it's blanked again, causing a fall off in average power.

    The blanking-induced power fall off only happens when I display images that have *lots* of blanked areas that are close together in the scan pattern. (Which means that the blanking is happening much more frequently in a given frame, like this one.) But even with the power fall off, the entire image is still displayed - just not as brightly. I never end up with "dead spots" in the pattern. Do you?

    Adam

  6. #16
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    Default

    The problem is that there are tails. Like the laser takes to long to light up and down. But what you say about low power have also happend if the laser have been off for a while. A warmup think I think.
    You know, I have one simple request. And that is to have sharks with frickin' laser beams attached to their heads!

  7. #17
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    Mar 2006
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    Default

    Hey Buffo, I see this as well with my Green laser... I can see when i go from frame to frame a BIG intensity difference depending on sometimes, just a few more blanking points.......Is this a common thing? I am using the Lambda Pro...

    I wonder if you see the same effect with all the DPSS Balnking? Would it make a difference if it was ANALOG Blanking Rather than TTL?
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  8. #18
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    Default Blanking issues

    Carey;

    Yeah, I know what you mean. Some frames display just fine, while others that are only slightly different show a pronounced difference in brightness. I've heard that this blanking-induced power loss is *very* common among the Chinese DPSS units.

    As to whether analog blanking would help the issue - I think the answer is "maybe", depending on how it's done. I spoke with Sam Goldwasser about this problem, and he said that the better DPSS units do not completely kill the current to the pump diode when they blank, but only drop the current to just below the lasing threshold for the Nd:YVO4 crystal. This is supposed to help the diode come back up to full intensity fast, since it is already idling. This also helps smooth the temperature curve as the unit switches off and on.

    He said that with a *good* TEC control circuit and a blanking circuit that idles the diode at just under lasing threshold for the Nd:YVO4 crystal, this problem will disappear. However, it seems that lots of manufacturers are taking the cheap route, which is why this problem is so common.

    I've got an older Lasever DPSS unit that I really need to do some experiments with. It has a very nice power supply, and I know it supports TTL blanking, but it might actually support analog blanking as well. I'd like to know if it suffers from the same power loss issue as the other Chinese laser I've got in my Alphalite projector. (Now if only I had more time to play...)

    Groover,

    RE: tails on some images. Have you played around with the blanking timing in the software? If you have tails on ALL frames, then I can see that being caused by the laser blanking being too slow. But if it's only on *some* frames, then maybe you just need to tweak the blanking timing a bit?

    Out of hundreds of frames, I have maybe 5 or 6 that show really bad tails when displayed. But those tails are there even at slow scan speeds; they just get longer when I crank up the pps... (I think the files are just screwed up.)

    By the same token, I can display the ilda test pattern at 50kpps with no tails, even at 10 degrees. I would think that if the laser wasn't blanking fast enough, I'd be seeing lots of errors on the test pattern at 50kpps... Do you have tails on the ilda test pattern when you display it at speeds above 20kpps?

    Adam

  9. #19
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    Default Re: Blanking issues

    Quote Originally Posted by Buffo
    Out of hundreds of frames, I have maybe 5 or 6 that show really bad tails when displayed. But those tails are there even at slow scan speeds; they just get longer when I crank up the pps... (I think the files are just screwed up.)

    Adam

    Sounds like there arn't enough anchor points at the end of each frame.. Just add some extra points
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