Page 1 of 2 12 LastLast
Results 1 to 10 of 11

Thread: Newbie (to this forum) have a couple of questions

  1. #1
    Join Date
    Sep 2006
    Location
    St. Louis, MO - US
    Posts
    83

    Default Newbie (to this forum) have a couple of questions

    Hello all,

    I am new to the forum but not new to lasers. I have spent many hours on other forums that deal with lasers in general (guess which one) but often found myself answering questions about analog modulation and PCAOMs. There are just a few people on the forum, myself included who can answer some of the more complex questions.

    But when it comes to my own questions, I get a reply "omg dude, i dont know what u mean".

    So, here are my questions! :)

    I've read around the forum and found the ratio for the near perfect white color balance is 4:1:2 (RGB). With this ratio in mind, does it really matter much if the red module is 635nm/650nm/671nm?

    Also, I'm familiar with the ILDA interface, at least the pinouts. I will be working on the repair and major modification of an RGB unit shortly but there is some confusion as to what it connects to. I've heard two things.

    1) The interface plugs into the 25-pin connector on a daughter card - (Pangolin, Bocatec etc.) which makes sense.

    2) You don't need that card! It hooks up to the LPT:1 printer port!

    Is that actually true?

    I've have numbered the pins in an Excel spreadsheet (1-25) and labeled the pins from both the ILDA pinout and the printer port pinout. It just doesn't look like it should work and I don't want to try this.

    If anyone is able to assist with this (either question) it will be greatly appreciated.


    Thank you in advance,



    Phil

  2. #2
    Join Date
    Jul 2005
    Location
    Flying over a town near you
    Posts
    1,404

    Default

    Sounds like the 25 pin d-sub connector for a DACsignal input........got any pix?
    You are the only one that can make your dreams come true....and the only one that can stop them...A.M. Dietrich

  3. #3
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,488,547

    Default Re: Newbie (to this forum) have a couple of questions

    Welcome to the group Phil!
    Quote Originally Posted by godfrey
    I've read around the forum and found the ratio for the near perfect white color balance is 4:1:2 (RGB). With this ratio in mind, does it really matter much if the red module is 635nm/650nm/671nm?
    There are two schools of thought on this issue. The "Physics major" viewpoint, and the "Arts major" viewpoint.

    The Physics major will quote you the specs of the Mark-I human eyeball. Basically, the human eye is roughly 2 times less sensitive to 650nm light than it is to 635 nm light. So if you want to use 650 nm light, your 4:1:2 ratio becomes 8:1:2.

    671 nm is even worse. The human eye is between 5 and 7 times less sensitive to 671 nm as it is to 635 nm. So now you're talking about a ratio somewhere between 20:1:2 and 28:1:2!

    The Arts major will point out the fact that "What looks good, *IS* good!" And to a large degree, he is correct. Most people won't see a huge difference between a system that is 100% color balanced and one that is not. (The one caveat here is that 671 nm really *is* approaching the absolute lower limit for human vision, so unless you've got BUCKETLOADS of power at that wavelength, you're probably better off sticking with 650 nm... Having said that, 671 nm makes some *very* cool colors when mixed with green and blue!)

    I used to believe that perfect color balance was paramount. However, after facing the reality that green is cheap, red is pricey, and blue is outrageously expensive, I decided to go ahead with what I had... As you can see from my avatar pic (or some of the other pics I've posted in the gallery), perfect color balance isn't always necessary. (All my pics are 14mw 632.8 red, 7 to 10 mw 532nm green, and 25 to 30 mw 488nm blue.)

    No doubt you've seen some of the less-expensive Chinese RGB laser projectors on E-bay that offer 300 mw of 650 nm red, 50 mw of 532 nm green, and 50 to 60 mw of 473 nm blue... Now, based on the specs of the human eye, these systems should exhibit terrible color balance. Nowhere near enough red, or blue for that matter! Yet I've seen one of these projectors in operation first hand, and I can tell you that they look great. The white is pure white. The yellow is yellow (not greenish at all). The teal is clearly a clean mix between green and blue. The pink/magenta is quite vivid. So perfect color balance isn't always that important.

    Bottom line: get as much red as you can afford, and stick to 650 nm or higher. Beyond that, get as much blue as is reasonable for your budget. But don't sweat it if you can't get half as much blue as you have red. You'll be fine with less. And if you have enough money left over to get some extra green - even if it blows your color balance all to hell - go ahead and do it. You can always dial the green back (assuming you've got analog modulation) when you want better color balance, yet you'll still have that extra power available to give your beam shows some real punch!

    Quote Originally Posted by godfrey
    Also, I'm familiar with the ILDA interface, at least the pinouts. I will be working on the repair and major modification of an RGB unit shortly but there is some confusion as to what it connects to. I've heard two things.

    1) The interface plugs into the 25-pin connector on a daughter card - (Pangolin, Bocatec etc.) which makes sense.

    2) You don't need that card! It hooks up to the LPT:1 printer port!
    Number 1 is correct. Well, mostly. The ILDA standard is indeed a 25-pin connector that passes ANALOG data between a projector housing and a controller. The projector housing is the box that holds the lasers, the galvos and amps, the safety shutter, and the color control equipment. (Color control equipment can include modulation of the laser power supply, use of a PCAOM, use of multiple AOM's, or even using a combination of galvo's and dichros.)

    A controller can either be a stand-alone unit that uses it's own procesor and memory to display a series of pre-set frames, or a digital-to-analog converter (or DAC) that connects to a computer (like the Pangolin QM2000 PCI card) and converts the digital signals from the computer to analog data that is sent to the projector.

    In either case, the 25-pin ILDA port is used to connect the controller to the projector. Remember that this is analog data. Variable X and Y positions for the scanners (in the form of an analog waveform), and variable color information to the color control equipment. (Assuming analog blanking is supported by the controller.)

    Number 2 is most certainly false. The parallel port on a computer is a *digital* data link. The ILDA standard connector is an ANALOG link between a controller and the projector.

    The confusion is that they both use 25-pin connectors. Also, many of the early DAC's used the printer port to communicate with the computer, which adds to the confusion. (Later DAC's used the ISA bus, then the PCI bus, and now even the USB ports on a computer.) But remember that there is no analog data on the PC's printer port. You *can't* connect a set of galvo amps directly to a PC's printer port!

    As an aside, there are several low-cost DAC's that still use the parallel port. The Alphalite, the Die4DAC, and even this home-built DAC that we were talking about earlier all use the parallel port to communicate with the control software on the PC. Note that all of these DAC's suffer from some inherent limitations of the PC's printer port, however. Most notable among these limitations are strobing, pauses, and hot spots in the scanned image caused by interruptions in the flow of data from the PC. It is because of these limitations that most laser show software has moved on to faster interfaces like the PCI bus and the USB port...

    Have a peek at some of the older messages here on Photon Lexicon and you'll find several discussions of color balance, and more than a few pictures showing you what a balanced (and an unbalanaced) system looks like. You might be surprised at the beauty of those unbalanced systems!

    Adam

  4. #4
    Join Date
    Sep 2006
    Location
    St. Louis, MO - US
    Posts
    83

    Default

    Adam. Thank you for the very comprehensive reply, it is very appreciated. In addition, thank you for clearing up the confusion on the printer port issue. I just knew it didn't sound right. If that was the case then why are we buying these expensive controller boards?!?

    I have not had the opportunity to work with this unit yet, but from what I've seen from a couple of photos taken from the inside - this unit is poorly built.

    RTV silicon and double sided foam tape hold components in place. This RGB projector unit was purchased for $1,050 new. There are two major factors as to why its so cheap. 1) Design and build quality. 2) NO IR FILTERS!! AHHHH!

    These issues need to be addressed! The first order is placing IR filters on the blue and green modules. The second is to purchase new optics mounts for the dichroic filters and cube prism which is used to combine the two red wavelengths.

    It will receive a major overhaul. I'm mounting all of the modules and optical components (even the scanner pair) on delrin. It's slightly cheaper than aluminum and has low thermal expansion.

    I can though, share with you my latest attempt to create (near) white light using two DPSS units and a Spectra Physics 163A-1202.

    Run of the mill red laser diode in a laser level (650nm or 671nm) 5mW
    Modded Leadlight 110 (532nm) about 20mW
    Spectra Physics 163A-1202 argon/ion (488nm) 20mW

    I used two sets of polarizing filters to reduce the output of both the green and blue lasers. I used a trichroic filter assembly that came from a broadcast field camera you see the news crews carrying around. The beams were aligned somewhat on target. Steering mirrors should make future setups more accurate...I'm working on making those.

    Anyway, enjoy the photos. *edit* resized photos...

    Phil







  5. #5
    Join Date
    Jul 2006
    Location
    Belgium
    Posts
    270

    Default Re: Newbie (to this forum) have a couple of questions

    Quote Originally Posted by godfrey
    I've read around the forum and found the ratio for the near perfect white color balance is 4:1:2 (RGB). With this ratio in mind, does it really matter much if the red module is 635nm/650nm/671nm?
    I've written a small application in the past that calculates the power levels for the three colors depending on the wavelengths and the relative sensitivity of the cones in the human eye.

    If I input 100mw of 532 nm green, then I have the following results for the various 'reds':

    Color RED GREEN BLUE
    Wavelength 632 532 473
    Power 361mW 100 mW 856 mW
    Ratio 3.6 : 1 : 8.5

    Color RED GREEN BLUE
    Wavelength 658 532 473
    Power 1288 mW 100 mW 856 mW
    Ratio 12.9 : 1 : 8.5

    Color RED GREEN BLUE
    Wavelength 650 532 473
    Power 827 mW 100 mW 856 mW
    Ratio 8.3 : 1 : 8.5

    Color RED GREEN BLUE
    Wavelength 671 532 473
    Power 2954 mW 100 mW 856 mW
    Ratio 29.5 : 1 : 8.5

    I want to point out that these are theoretical values. Ratio's others than the theoretical ratio's can appear very realistic.

    Because there has been said lots of things about the wavelength that should be taken for red, I would like to add a remark on that behalf too.
    As stated in many forums, it is true that using 632nm for the red implies that less power has to be used to match the green light source. But... there is also something like the color gamut. Everyone knows that a tv for instance cannot represent all possible colors. This is because of the use of three primary colors and the choice of the wavelengths of those primary colors. By selecting appropriate primary colors, it is possible to extend the color gamut, enabling to display more colors than with other primary colors.
    To choose the wavelength you want, you have to consider the tradeoff between color gamut and power (cost).

    Some interresting links on this subject:
    http://cvision.ucsd.edu/basicindex.htm
    http://www.handprint.com/HP/WCL/color1.html

  6. #6
    Join Date
    Sep 2006
    Location
    St. Louis, MO - US
    Posts
    83

    Default

    jeejeedr,

    Thank you for the information and the URL's you have at the bottom of your post. I will have to read those tomorrow after I get some sleep!

    I took a look at your formula, and have a quick question.

    Why is blue always represented as 856mW? Wouldn't that be a little excessive or does it have to do with the relative sensitivity of our eyesight.



    Phil

  7. #7
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,488,547

    Default

    Hey Phil;

    No problem. PhotonLexicon is all about helping people enjoy their lasers. Glad to help.

    Regarding the cheap mounting solutions in your new projector, yeah... That's pretty typical of a lot of the Chinese units. And I agree that it really sucks. Kudo's to you for taking on the challenge of re-mounting everything. Should be quite nice when you finish. And I agree that IR filters should be standard. I can't imagine why they don't include them.
    I'm mounting all of the modules and optical components (even the scanner pair) on delrin. It's slightly cheaper than aluminum and has low thermal expansion.
    Hmmm... Delrin eh? Isn't that some sort of plastic / epoxy / composite material? I'll bet the thermal conductivity is really low with that stuff. While heat isn't really an issue for the optical mounts, the laser modules themselves (and the scanners for that matter) usually prefer to be mounted on something that can conduct the heat away quickly. Just a thought...
    I can though, share with you my latest attempt to create (near) white light using two DPSS units and a Spectra Physics 163A-1202. <snip>
    The beams were aligned somewhat on target.
    Somewhat on target? Hardly... You did a GREAT job of aligning that rig! Very nice pictures. I see that the far-field alignment was a little off, but it still looks great. With a few diffraction gratings, you could have been doing some cool effects with that setup...

    Adam

    <edit>
    PS: The reason the blue power level doesn't change in any of the scenario's listed in jeejeedr's post above is that the wavelength of the blue laser is held constant at 473 nm for all examples. Since the wavelength doesn't change, neither does the power level needed to equal the brightness of the 100 mw of 532 nm green. The only wavelength that changes is the red, and thus the red power level changes with each example.

    I do have a problem with the calculation, however. It assumes that the human eye has an infinite intensity range, and that the range is linear. Neither of which is actually true. In fact, once you get over a few hundred milliwatts of power in a spot projected on the wall, your retinas will begin to saturate, making it increasingly difficult to notice the next increase in power. In practice, 400 mw of blue will look almost as bright as 600 mw of blue, because your eyes will be saturated by the high intensity.

    Granted, if you have beams sweeping around in a large room, then the extra power *WILL* be noticeable, since you're spreading it around so much. But for graphics projected on a wall, the eyes will begin to saturate long before you get to that 856 mw level.

  8. #8
    Join Date
    Jul 2006
    Location
    Belgium
    Posts
    270

    Default

    Quote Originally Posted by godfrey
    jeejeedr,

    Thank you for the information and the URL's you have at the bottom of your post. I will have to read those tomorrow after I get some sleep!

    I took a look at your formula, and have a quick question.

    Why is blue always represented as 856mW? Wouldn't that be a little excessive or does it have to do with the relative sensitivity of our eyesight.



    Phil
    The blue is always 856 mW because the wavelength for the blue stayed the same in all calculations. The wavelengths relative sensitivity ratio used for blue (473 in my calculations) is 0.1033674000000 compared to 0.8849624000000 for 532nm green, giving 856 mW of 473nm blue for 100 mW of 532nm green, no mather what kind of red is used.

  9. #9
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,488,547

    Default

    Ha ha!

    Jeejeedr - you must have posted seconds after I finshed my edit! Oh well.

    I also should point out that the 4:1:2 ratio assumes that you're using 488 nm light for blue. Dropping to 473 nm increases the amount of blue you need. (Just goes to show you that the human eye is actually pretty bad at viewing ANYTHING in the blue spectrum...)

    Adam

  10. #10
    Join Date
    Jul 2006
    Location
    Belgium
    Posts
    270

    Default

    Quote Originally Posted by Buffo
    Ha ha!

    Jeejeedr - you must have posted seconds after I finshed my edit! Oh well.
    I did

    Quote Originally Posted by Buffo
    I also should point out that the 4:1:2 ratio assumes that you're using 488 nm light for blue. Dropping to 473 nm increases the amount of blue you need. (Just goes to show you that the human eye is actually pretty bad at viewing ANYTHING in the blue spectrum...)
    I love however 473 for the deep blue you can make with it. It's just a shame you need more power...

    Regarding your comment on the appearance of the different power levels: I always start from the idea that it will be used for beam at a certain moment in time. As beams depend on particles in air for reflection, the power difference will be noticable. For graphics on a wall some meters away, even a 250 mW RGB projector will do the job (even nicer).

    The calculations were merely examplary for demonstrating the ratio's. They need to be transposed to match the needed total power which is dependant on the application.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •