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Thread: Galvo/Amp Upgrade

  1. #21
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    Quote Originally Posted by jdavis7765 View Post
    I thought I would be able to cut a 2x2 block of aluminum with metal blade on circular saw (metal blade), but maybe I was wrong :/.
    I have successfully cut 1/4 inch thick aluminum plate using a table saw with a carbide-tipped blade, but this is admittedly a risky task. You need to go very slow! If you overload the saw it can violently kick the plate back at you, potentially causing serious injury. Also, this only works with aluminum. Do *not* try it with steel. (Trust me on this - you will have a very bad time if you try it with steel!)

    In theory you could do the same thing with a circular saw, but again, it's risky. For sure you'd want to have the aluminum plate clamped down really firmly before you started, and again you need to go slow with the skill saw. But a carbide-tipped blade will cut through aluminum reasonably well provided you take the appropriate precautions.

    Note that this only applies to cutting plate. Cutting a 2 inch thick piece of solid aluminum is probably beyond the abilities of your average hobbyist unless you happen to have a mini mill or a really nice band saw. If you need to work with material that thick you probably want to take it to a machine shop.

    I did look at the diagram but for some reason it did not register that the one view shows the beam entering and the height at which it should enter.
    OK, but you see it now, right? The Compact 506 scanners have a beam entry height of 25 mm if you come in from the right and hit the top mirror first, or a beam entry height of 18 mm if you come in from the left and hit the bottom mirror first. (To do the "left entry" the block has to be rotated 90 clockwise.) All of this assumes that you are facing the block with the output beam coming straight at you.

    If I were thinking about upgrading the lasers at any point, is there any website that sells them you could recommend or even recommended lasers? When I say upgrade, i do not mean higher power, I quite like where I am at now. I just wonder if I can get better color from better lasers vs what I have now.
    There are several suppliers, sure, but I'm not sure exactly what you're wanting to improve.?. I thought the lasers in your projector already supported analog color modulation... If so, then you should be able to dial in just about any color you want. Or is there another problem with color that you're referring to?

    Usually when people ask about getting "better color" it's because they're looking to get rid of subtle modulation issues that can leave "tails" or other artifacts in graphics shows - particularly when parts of an image have the intensity faded down very low. Fixing issues like this is normally a matter of switching to a better diode driver for the lasers. Is that what you're talking about?

    Adam

  2. #22
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    Quote Originally Posted by buffo View Post
    I have successfully cut 1/4 inch thick aluminum plate using a table saw with a carbide-tipped blade, but this is admittedly a risky task. You need to go very slow! If you overload the saw it can violently kick the plate back at you, potentially causing serious injury. Also, this only works with aluminum. Do *not* try it with steel. (Trust me on this - you will have a very bad time if you try it with steel!)

    In theory you could do the same thing with a circular saw, but again, it's risky. For sure you'd want to have the aluminum plate clamped down really firmly before you started, and again you need to go slow with the skill saw. But a carbide-tipped blade will cut through aluminum reasonably well provided you take the appropriate precautions.

    Note that this only applies to cutting plate. Cutting a 2 inch thick piece of solid aluminum is probably beyond the abilities of your average hobbyist unless you happen to have a mini mill or a really nice band saw. If you need to work with material that thick you probably want to take it to a machine shop.
    Yeah, I got the block in the mail today and I do not think this is something I want to do on my own. I think I will just get the measurement and pop into a local machine shop to see if they can cut it for me.



    Quote Originally Posted by buffo View Post
    OK, but you see it now, right? The Compact 506 scanners have a beam entry height of 25 mm if you come in from the right and hit the top mirror first, or a beam entry height of 18 mm if you come in from the left and hit the bottom mirror first. (To do the "left entry" the block has to be rotated 90 clockwise.) All of this assumes that you are facing the block with the output beam coming straight at you.
    Yes, I see it now, should be fairly easy to measure once I get the beam height.



    Quote Originally Posted by buffo View Post
    There are several suppliers, sure, but I'm not sure exactly what you're wanting to improve.?. I thought the lasers in your projector already supported analog color modulation... If so, then you should be able to dial in just about any color you want. Or is there another problem with color that you're referring to?

    Usually when people ask about getting "better color" it's because they're looking to get rid of subtle modulation issues that can leave "tails" or other artifacts in graphics shows - particularly when parts of an image have the intensity faded down very low. Fixing issues like this is normally a matter of switching to a better diode driver for the lasers. Is that what you're talking about?

    Adam
    I suppose maybe my ignorance got the best of me. I guess what I am referring to is the blending of colors (assume this would be the effect of modulation) when comparing laser to program on the computer. I know it will not be 100 percent accurate, it just sometimes appears "off". Do you have a an example of the "tails" you referred to?

  3. #23
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    Quote Originally Posted by jdavis7765 View Post
    I think I will just get the measurement and pop into a local machine shop to see if they can cut it for me.
    With luck the beam height of the lasers will be equal to or greater than the beam entrance height for your scanners. Then you can just shim the scanner block up if needed using several layers of sheet metal, which you can cut yourself.

    But yeah, if the laser height is lower than the beam entrance elevation for the scanner block then your best bet is to take the scanner block to a shop and have them shave it.

    what I am referring to is the blending of colors (assume this would be the effect of modulation) when comparing laser to program on the computer.
    The quality of the color blending you see in the output is directly related to the quality of the laser diode drivers. If the analog modulation response of the driver is linear, you should see great color blending. On the opposite end, a pure TTL driver (so on-off modulation only) will only give you 7 possible colors. Most analog drivers show at least some non-linearity, but any analog modulation ability (even from a really cheap driver) is still going to look worlds better than TTL modulation. But yeah, better drivers = better color gradients.

    Don't forget that you can also tweak your color settings in software. Often a little software adjustment can largely correct the limitations of a cheap analog driver. For example, if you notice that your orange looks more like yellow, or if your white has a greenish tint to it, these are things you can tweak in software. Some software will also allow you to adjust the modulation curve throughout the range from 0 to 100% output, which is even more helpful.

    Do you have a an example of the "tails" you referred to?
    I had to do some digging, but I found a few examples. (Funny how people never seem to save pictures that show a problem!)

    In this post, have a look at the 3rd picture which shows a green question mark being displayed. The dot beneath the question mark has a pronounced tail where the laser did not turn off at the point when the dot was fully drawn. The is the most common example of a "tail", and it can usually be fixed by simply adjusting the blanking offset value in software. However, if you have wildly miss-matched drivers you may need to install a delay circuit to match up the response times. (This was a bigger problem back when we had both DPSS and direct-diode lasers in the same projector, but nowadays nearly all projectors use all direct-diode lasers.)

    Another, more subtle example of tails can be seen in this post. Here the effect is harder to notice, but if you look at the starting and ending points of the white line segments you can see a small yellow tail on some of them, and a very tiny blue tail on some as well. The corrected picture to the right isn't perfect, as there are still a few blue tails visible, but it's much better than the initial picture. Fixing this problem required the addition of the delay circuit I mentioned above.

    If you're experiencing tails as shown in the first example (the question mark picture), then you can probably fix that by adjusting your blanking offset. But if you have tails and/or blending artifacts that look more like the second example, then you'll either need to install a delay circuit on each of the 3 color modulation inputs to the projector, or you'll need to replace the laser drivers with ones that have superior modulation response.

    But again, before you start pricing new drivers be sure you've tried to adjust your colors in software first, because most modern laser show software includes several settings that can be used to tweak your color modulation.

    Adam

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    So, got my block of aluminum and machine shop said 130 dollars to cut. I went and bought aluminum cutting blade for miter saw, secured black to saw with clamp, put cinder block in between me and saw for safety and it cut through like butter. Got that done and holes drilled to mount and it seems like I have the tails you are referring to, only these appear to be cause by galvo block placement. If I slide the block toward or away from the back or front of projector, it moves to the top of the bottom. It looks like there is a sweet spot but with my limited abilities it will take quite a few attempts to get right. This leads me to think, did I get the wrong size mirrors? Should I have went with 5mm instead of 4 as it may have been easier to align? It seems to be more pronouced on red than any other color as well, not sure what that indicates as the blue beam appears to not be circular yet it looks more like a small vertical rectangle so I figure that would have more spill off on mirrors. Let me know what you all think.
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    Quote Originally Posted by buffo View Post
    With luck the beam height of the lasers will be equal to or greater than the beam entrance height for your scanners. Then you can just shim the scanner block up if needed using several layers of sheet metal, which you can cut yourself.

    But yeah, if the laser height is lower than the beam entrance elevation for the scanner block then your best bet is to take the scanner block to a shop and have them shave it.



    The quality of the color blending you see in the output is directly related to the quality of the laser diode drivers. If the analog modulation response of the driver is linear, you should see great color blending. On the opposite end, a pure TTL driver (so on-off modulation only) will only give you 7 possible colors. Most analog drivers show at least some non-linearity, but any analog modulation ability (even from a really cheap driver) is still going to look worlds better than TTL modulation. But yeah, better drivers = better color gradients.

    Don't forget that you can also tweak your color settings in software. Often a little software adjustment can largely correct the limitations of a cheap analog driver. For example, if you notice that your orange looks more like yellow, or if your white has a greenish tint to it, these are things you can tweak in software. Some software will also allow you to adjust the modulation curve throughout the range from 0 to 100% output, which is even more helpful.



    I had to do some digging, but I found a few examples. (Funny how people never seem to save pictures that show a problem!)

    In this post, have a look at the 3rd picture which shows a green question mark being displayed. The dot beneath the question mark has a pronounced tail where the laser did not turn off at the point when the dot was fully drawn. The is the most common example of a "tail", and it can usually be fixed by simply adjusting the blanking offset value in software. However, if you have wildly miss-matched drivers you may need to install a delay circuit to match up the response times. (This was a bigger problem back when we had both DPSS and direct-diode lasers in the same projector, but nowadays nearly all projectors use all direct-diode lasers.)

    Another, more subtle example of tails can be seen in this post. Here the effect is harder to notice, but if you look at the starting and ending points of the white line segments you can see a small yellow tail on some of them, and a very tiny blue tail on some as well. The corrected picture to the right isn't perfect, as there are still a few blue tails visible, but it's much better than the initial picture. Fixing this problem required the addition of the delay circuit I mentioned above.

    If you're experiencing tails as shown in the first example (the question mark picture), then you can probably fix that by adjusting your blanking offset. But if you have tails and/or blending artifacts that look more like the second example, then you'll either need to install a delay circuit on each of the 3 color modulation inputs to the projector, or you'll need to replace the laser drivers with ones that have superior modulation response.

    But again, before you start pricing new drivers be sure you've tried to adjust your colors in software first, because most modern laser show software includes several settings that can be used to tweak your color modulation.

    Adam

  5. #25
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    Quote Originally Posted by jdavis7765 View Post
    it seems like I have the tails you are referring to, only these appear to be cause by galvo block placement
    The tails I mentioned in my previous post are artifacts in the displayed image on the wall. They are caused by the timing of the lasers not being sync'd to the galvos. So you have a situation where the galvos are still trying to get to the point where the laser should turn on, but the laser turns on too early and the line that should be blanked ends up being partially lit. Or, if the laser timing is late, then the galvos have gone past the end of the line and are now heading off to another part of the image, but the laser is still on so again part of the line that should be blanked ends up being partially lit.

    I can't understand how moving the galvo block would cause tails like this in the displayed image. Also, the picture you posted only shows a single vertical red line with clearly-defined end-points, so that doesn't really look like the tails that I was talking about.

    If I slide the scanner block toward or away from the back or front of projector, it moves to the top of the bottom.
    What is the "it" that you are referring to? Are you, perhaps, seeing a line that is coming out of the top of the projector that ends up being projected on the ceiling? That is, you have the normal image being displayed on the wall, but you also have a line that is "leaking" out of the top of the scanner block? (Roughly 90 degrees from the normal projection direction?)

    If that's what you've got, then yes, the problem is that your scanner mirrors are not wide enough to capture the full width of your lasers. This isn't a huge concern so long as the amount of red that is "spilling" off your scanner mirrors isn't excessive. Basically, if you still have enough red in your output to get a decent color balance, then as long as you have a lid on your projector it will block that line of red light that is coming out of the top of the scanner block. No one will ever see it.

    Should I have went with 5mm instead of 4 as it may have been easier to align?
    It's not so much an alignment problem as it is a beam diameter problem. People forget that the mirrors have to move through a range of angles. With the mirror at a 45 degree angle to the beam, you need a mirror that is at least 5.7 mm wide to capture the full width of a 4 mm beam. But as you rotate the mirror closer to horizontal, the required mirror width needed to capture the full beam increases dramatically. At 30 degrees you need an 8 mm mirror, and at 20 degrees you need an 11.7 mm mirror. And yes, each of these examples assumes an otherwise absolutely perfect alignment. Normally you want at least little wiggle-room beyond that point because perfect alignment is not easy!

    Most scan systems have a max optical scan angle of around 60 degrees, which means the scanner mirrors need to move 30 degrees. That's +/- 15 degrees on either side of the perfect 45 degree middle point. So the worst case in this example is when the mirror is at the 30 degree point (that's 45 minus 15), and that means you need at least an 8 mm mirror if everything else is perfect in order to capture the entire width of the 4 mm beam. In practice, you probably want a 9 or 10 mm wide mirror to be on the safe side.

    So yeah, if you had gone with 5 mm aperture mirrors you probably would have had an easier time. However, as I mentioned above, so long as you aren't losing a great deal of light you can live with the problem because the projector lid will block any part of the beam that spills off the scanner mirrors.

    And again, all of this assumes that the "tails" problem you're describing is actually part of the beam spilling off the scanner mirrors and leaking vertically out of the scanner block to create a line on the ceiling. That's not "tails", that's spillage. If my understanding of your problem is incorrect, then please post additional pictures and we'll try to figure things out.

    Adam

  6. #26
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    I will try to do a better job explaining. The issue is only with the red laser. When single points are projected it is more pronounced and always manifests as a vertical line either to the bottom or the top of the point. If I move the scanners forward and backwards in the case this vertical line moved to the top or the bottom of the point. When complex visuals are displayed the lines dissapear as I am sure this is because the laser is not dwelling on a single bright point but is spread over a larger area?

    I do have some spill off that shoots vertically, but the older scanners did this so I assumed it was probable these would too.

    I belive that I only have two options (If my thoughts are correct about the mirrors being too small), precisely align the scanners in the center of the spill off or return the galvos for a 5mm set. The latter I really do not want to do as I would be wasting peoples time by not doing my own research from the beginning. I guess I just wanted to see if I was correct in my assumption.

    A few curious questions... Is beam diameter correlated to beam power or is it pretty much just something you decide when purchasing a laser? So if I, for instance, wanted to purchase another red laser with a smaller beam diameter, would that be feasable? Probably will not do it, just curious.. Also, we had talked about laser amps, is there a site you could recommend buying from if I wanted to upgrade and are they something that can just be replace easily or do I have to match laser voltage etc.

    Again, thanks for sticking with me and answering all of my newbie questions! I really do appreciate it.

  7. #27
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    Artifacts like that can be due to either issues with the collimation of the laser diode, or the near field alignment being off and the spot hitting the edge(s) of the galvo mirror (or the spot just being too big). If the artifacts look the same across the entire scan field, then it's almost certainly the first problem. It also just looks like beam artifacts from your photo.

    Getting a nice beam out of diode lasers, especially multimodes, is tricky. The raw diode, despite being a laser, kinda just poops light like an LED, and you'll need a collimating lens to convert that poop into a nice beam. Due to fundamental limitations in optics, there is only so good you can make the beam, especially if you need to fit the whole diode and optical assembly in a reasonably-sized module or projector. There will almost always be a certain amount of spill from light that the collimator can't wrangle into the beam, which usually shows up as a faint glow around the spot, and sometimes the spot itself has little sticky-outy bits of higher intensity light from the main spot. The glow is usually not intense enough to notice in use, as you've seen, but human eyes have really good dynamic range and we can often perceive it when the spot is static. Because that that spill has a much higher divergence than the beam of interest, it drops off much more rapidly in intensity than the beam, so as you get farther from your projection surface it will be less visible.

    Going to a larger set of mirrors on your galvos will help if your problem is that the spot is too big for what you have and the mirror edges are causing your trouble, but if the diode collimation is the problem, then bigger mirrors may actually give you more spill out the front and make things slightly worse, depending on what the beam characteristics actually look like. If the problem is your near field alignment causing the red to fall off the galvos while the G&B are centered, then ideally you want to fix your near field alignment. Going to bigger mirrors would of course help with that, but that's kind of a sledgehammer fix.

    Beam diameter and divergence are linked by conservation of etendue. Basically, you can't reduce the spot size without commensurately increasing the divergence, and vice versa. Low divergence requirements necessarily implicate a large diameter requirement, all else being equal. But you may be able to find a red module (or a different correction strategy) that gives better results. It's hard to tell exactly how bad this sort of thing is from photos. Getting REALLY good beam quality generally requires shifting technologies, either going from multimode diode to single mode diode, or from direct injection diode to something else, but generally that sort of shift means giving up a lot of power or going way up in price--sometimes both.

  8. #28
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    Quote Originally Posted by jdavis7765 View Post
    When single points are projected it is more pronounced and always manifests as a vertical line either to the bottom or the top of the point. If I move the scanners forward and backwards in the case this vertical line moved to the top or the bottom of the point.
    OK, that sounds like the beam is just barely spilling over the edge of the scanner mirror and the line artifacts you are seeing are caused by refraction as the beam spills off the edge. Moving the scanner block in or out changes the mirror edge that the beam spills off of, which is why the line flips from top to bottom.

    There are a couple things you can do to fix this... For starters, larger scanner mirrors will help. But that's a lot of work to pull everything out and swap things, and you may still have some artifacts present due to the imperfect collimation of the red multi-mode diode. In my opinion a better option is to install a spacial filter.

    Basically this is a pair of identical lenses in a keplerian collimator arrangement (so you have a focal point in the middle and no change in beam diameter from input to output) with a movable pinhole (that's the spacial filter) in the middle. As you move the pinhole from the focal point in the center to a position closer to the input lens you will progressively mask off more and more of the outer portions of the beam. This will allow you to clean up the beam profile to remove any artifacts and it will also reduce the beam diameter slightly before it hits your scanners. That way the beam fits more comfortably on the scanner mirrors and you don't have any stray artifacts. Once you find the sweet spot for the pinhole between the two lenses you can mount it permanently in that location.

    When complex visuals are displayed the lines disappear as I am sure this is because the laser is not dwelling on a single bright point but is spread over a larger area?
    Yeah - even a really messy beam will blend into a fairly uniform-looking line when the scanners are busing drawing lots of complex shapes. But if you are displaying a simple point (like a "hot beam" cue), any beam artifacts will be more apparent.

    Is beam diameter correlated to beam power or is it pretty much just something you decide when purchasing a laser?
    Tough question to answer, as there are lots of variables. For a given range of power there are really good (and expensive) lasers that have the best beam characteristics and there are cheaper lasers that have poor beam characteristics. But the power range has an effect as well, because once you transition into the multi-mode diodes there's only so much you can do no matter how much you spend on optics.

    So while you might be able to get a 50 mw red beam in anything from 1 mm to 6 mm, if you want 2 watts of red the smallest beam you'll find is likely to be around 4 mm, if not more. Well, that's for direct-injection diodes anyway. Gas lasers, OPSL, and DPSS lasers are another story!

    So if I, for instance, wanted to purchase another red laser with a smaller beam diameter, would that be feasable?
    Do you know what the rated output power of your red laser is? I'm guessing it's somewhere between 200 mw and 500 mw... If so, then yes, you could probably purchase a replacement module that had a better (narrower) beam profile.

    we had talked about laser amps, is there a site you could recommend buying from if I wanted to upgrade and are they something that can just be replace easily or do I have to match laser voltage etc.
    Are we talking about laser diode drivers (the electronic circuit that powers the diode and controls the modulation), or scanner amps (which control the movement of the scanner mirrors and are matched to the individual scanners)?

    If you mean replacement diode drivers there are several options, but many of the DIY folks here have nothing but good things to say about the BBE driver, which sells for under $30. As for matching the drivers to the diodes, there are two things to consider: 1) the supply voltage to the driver must be at least a volt or two higher than the forward voltage drop across the laser diode. 2) the max current output of the driver must be equal to or greater than the max current draw of the laser diode.

    Normally the voltage supply isn't an issue when you are replacing drivers, since the existing driver should already have the appropriate supply voltage routed to it. As for the current rating, as long as you select a driver that is in the proper range you should be OK. So if the max laser current is 1 amp and all you have is a driver that goes up to 2 amps, you're still OK. I think the BBE driver comes in a few different current ranges - up to 500 ma for single mode diodes on the low end, and up to 2.5 or 4 amps for larger multi-mode diodes on the high end.

    Note that at some point before you install the new driver you will need to look up (or measure) the max current of the existing driver with the modulation input at 100%. That way you can adjust the gain on the new driver so that 100% modulation input yields the same output current to the diode as before with the old driver. If you don't do this you could easily over-drive your diode and destroy it with the new driver.

    thanks for sticking with me and answering all of my newbie questions! I really do appreciate it.
    No sweat dude - that's what PhotonLexicon is for.

    Adam

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    Thank you for the reply buffo! I think I am plaugued with a few problems now. I was able to fix the red beam artifact by undoing one screw from galvo block and twisting a bit (I know this is a hack fix, but it works). I still have a little spill off, but nowhere near as bad as before. The other problem I noticed (which happens regardless of the galvo block being rotated or not) is the blue laser has a vertical rectangular shape to the beam so this spills off the first mirror is hits (y mirror?) causing a spill off on it. Not sure how I didnt notice before. Also, the blue laser light seems to be signifigantly fatter that green and red.

    Buffo, you had mentioned using a keplerian collimator and a pin hole. Looks like this can be used to expand or contract a laser beam size, correct? Then the pinhole will only allow the laser to pass through and come out perfectly circular? Maybe this is a tough question to answer, but where exactly would I purchase this at? I found https://www.edmundoptics.com but seems like there are many things to pick through. Do you have any information that could help me decide what I need or is this fix sort of a custom solution?

    To be honest I was thinking of taking the easy way out and purchasing an RGB collimated laser module, but then too I am worried about the specs I need to look for so the beam size would be compatible with my 4mm galvo mirrors. My mind is all over the place, ahhhh! lol Guess this is what I get for upgrading lasers instead of buying a good brand from the get go. I suppose I would not learn anything with the former. hehe

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    Quote Originally Posted by jdavis7765 View Post
    the blue laser has a vertical rectangular shape to the beam so this spills off the first mirror
    This is a common beam profile for multi-mode diodes, especially the 445 nm blues. Basically the emitter is rectangular so you have two different divergence numbers, one for the narrow axis of the emitter and one for the wide axis. The narrow axis of the rectangular emitter will have the worst divergence. (Between 3x and 8x higher divergence than the wide axis of the emitter.)

    Some lasers use a set of secondary optics to help tame this "fast" axis. The idea is to use a pair of cylindrical lenses or anamorphic prisms to expand the fast axis and then re-collimate it so it's close to the size of the other axis. By expanding the beam in only that one axis you reduce the divergence in only that one axis. So long as you position these secondary correction optics really close to the laser (before the narrow axis has diverged too much) you can widen the beam in that axis so it's close to the width of the the beam in the other axis. Then when you re-collimate that axis it should have close to the same divergence as the "slow" axis.

    the blue laser light seems to be signifigantly fatter that green and red
    As a general rule, the beams from the blue multi-mode diodes are fatter than the beams from the multi-mode greens and reds. However, you may want to check the primary collimation lens on your blue laser. If it is adjustable, it's possible that it has moved slightly from the optimal setting.

    The primary collimation lens is usually just a standard AR-coated aspheric lens mounted in a threaded housing. If it is adjustable you should see either a slot on the lens holder or possibly a small hole near the edge that you can grab with a pointed pick. Rotating the threaded lens holder will move the lens in or out relative to the diode emitter which will change the focus. Try to get the smallest spot size you can at a distance of ~ 15 ft from the projector.

    Buffo, you had mentioned using a keplerian collimator and a pin hole. Looks like this can be used to expand or contract a laser beam size, correct?
    A Keplerian collimator can be used to expand or contract the beam diameter, yes. But in this application the idea is to use identical lenses on either end of the collimator so the output beam is identical to the input beam. The idea is not to change the beam diameter but to position a spacial filter (the pinhole) at the focal point in the middle between the two lenses. This allows you to "carve out" the center of the beam. And since the beam is converging to a point as it passes through the pinhole, any stray light that diffracts around the edge of the pinhole will spread out far enough that it will completely miss the second lens and thus will not be present in the output beam.

    Then the pinhole will only allow the laser to pass through and come out perfectly circular?
    Yes, exactly. I should point out that the pinhole is not really as small as a pin. It's just a small diameter hole that will only allow the center portion of the beam to pass. Normally the hole is made a bit larger than the beam diameter at the focal point. Then by moving the pinhole closer to the first lens (where the beam is still converging) you begin to filter out more and more of the outer edges of the beam. When you get to the beam profile you want, you lock the pinhole in that position.

    Maybe this is a tough question to answer, but where exactly would I purchase this at?
    You can buy the lenses from Edmund Optics, or Thorlabs, or any other supplier, but you will need to mount them and position them yourself. You'll also need a thin sheet of metal with a tiny hole in it that you will mount between the two lenses. The focal length you choose will determine how far the two lenses need to be positioned from each other (basically they will be twice the focal length apart). This lens has a 2 cm focal length (OK, technically 19 mm), so that gives you 4 cm between the pair. $70 for two of them. You could go with a shorter focal length, but alignment becomes more crucial as the distance between the lenses gets shorter and shorter, so I would not go shorter than 1 cm for the focal length (giving you a 2 cm gap to work with).

    If you don't want to try to make your own mounts for the lenses then you'll need to buy those, which adds to the cost, but again any optics supplier can provide those. You can even buy the lenses already mounted in metal barrels to make them easier to mount if you want. The lenses should be identical positive lenses (plano-convex) that are AR coated for visible wavelengths with a diameter at least a couple mm wider than your beam width and with a focal length that, when doubled, will allow you enough room to position the pinhole in the middle while still fitting the whole mess somewhere in the beam path between the last dichro and the scanners inside your projector.

    is this fix sort of a custom solution
    Most definitely a custom solution! But it's not terribly expensive or difficult, and it will be a good learning experience.

    I was thinking of taking the easy way out and purchasing an RGB collimated laser module, but then too I am worried about the specs I need to look for so the beam size would be compatible with my 4mm galvo mirrors.
    Most commercial RGB modules list the beam diameter and divergence, so it's easy to make sure that whatever you buy will work with your scanners. Be sure to measure the width of your mirrors first though, because there is a big difference between a 4 mm wide mirror and a 4 mm *aperture* mirror. (Because the mirror is positioned at an angle to the beam the mirror must be wider than the beam to capture the whole beam.)

    Adam

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