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Thread: mRad calculation

  1. #11
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    Brad,
    I agree with tribble, but I also looked back at your comparison of the DPPS green projector with the diode green projector in your last pair of images. The "too tall" 520 is actually closer to the 445 in beam size. but because the 445 is much less visible the weak halo in the first image is missed and the line "looks" tighter, but it hardly is. Also notice in your very first image in your first post. The red is your tightest beam and this is (in my experience) the most divergent beam. I think Omar needs to focus the blue better as well. Finally, measuring off the screen and making the assumption that any blooming by the camera is not too different for the three colors, I measure the blue at aprox 2.5 mrad and the red at 1.5mrad. What did Omar specify the divergence of the projector to be?

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    Only thing I am finding for specs on the web site is <1.0mR (full angle) for a Pluto outfitted with the same 680mw of 637, 900mw of 520 and 445. In another configuration of Pluto that contains the same red and green but the new 462 blue, it says <1.6mR (full angle). Yes, I too think the blue seems a bit large as well but not as bad as the green. I would think it perhaps odd that two of the three would be out of alignment unless the projector took a pretty good jolt in shipping from DHL somehow. I suppose it's possible but, I trust Lightspace enough that it probably didn't leave the factory looking this way. The red is nice and tight though, just like the other Pluto's I own.

    Omar did say in an e-mail that:

    "And about the 520nm green, it is normally bigger divergence than the 532nm green(usually 0.5-0.7mrad), the 520nm green we made it about 1.0mrad.

    I check your photos of the outputs, this green divergence should be 0.3*1.0mrad, that is why you see one axis is bigger! I just talked with our technicians and been told that to ensure higher power of the 520nm green, they are using another lens, and without prisms in this green module! If use the prisms, it will be about 100mw less after opticals. So if you don' t like this green diode, I can arrange to send you another one with prisms(smaller divergence)..."

    I told her yes, I'd like to swap out the diode module with prisms. 2.77 isn't going to cut it. I may see what she thinks about the 462 blue as well.

    (I still love these Pluto's - even with the ocassional hiccup - and Lightspace has been great to work with.)

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    Interesting.... mine will arrive any day now. I'll make some measurements on my own and post the results.

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    Yes, it will be interesting to see if the ratios are similar as well as the actual numbers. I'm also curious as to the size of the scanner mirrors in these projectors and if the beams have been sized to adequately fill these mirrors.

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    Quote Originally Posted by planters View Post
    Yes, it will be interesting to see if the ratios are similar as well as the actual numbers. I'm also curious as to the size of the scanner mirrors in these projectors and if the beams have been sized to adequately fill these mirrors.
    I got the new PT-A40 wide angle scanners in these two new Pluto's. You can open them up at least 10 degrees wider that the regular PT-40's. The mirror shape is different naturally and here is a link to the dimentions:

    http://www.eightonlight.cn/products/.../0418/342.html

    This morning I set up an original Pluto with the PT-40's along with a new one with the PT-A40's and, the width of the edges of the test pattern are at least 20 feet wider. I believe it's PT's answer to the DT40wides. At some point I'll compare the two with one of my projectors that has the DT40wides in it. I still feel a bit like it's all treading water until the 506's are really "ready for prime time" retail sales.

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    Thanks for the quick feed back. I wish Bill would chime in here because he has the CAD program that will show any particular mirror set as it is scanned through its range and how the beam is projected onto each surface. Based on all the files he has sent me, I suspect that the "X" mirror is adequate for an unvignetted 5mm square profile beam. However, I am pretty sure that the "Y" is too short even for a 3mm beam because of the very wide scan angle. I may be wrong here. I'm only guessing.

    Part of the problem is that when the laser hits the shaft the light reflects in a large, distorted area in the far field and so the "Y" mirror may only have about 9mm of clear aperture and then only this much if the beam is small enough to fully use the distal end where the mirror is beveled at the corners. The "X" scans the spot pretty widely onto the "Y" over the short distance between these two mirrors.

    I would not change anything however, until these can be replaced by the 506's. The larger and appropriately sized mirrors of the 506's will allow full, uninvented 5mm beams and with that kind of beam width the largest line in your first post should be 1/2 the width of your red.

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    So if I am understanding you correctly, your hypothesis as to why I'm getting such fatter lines than I think I should is more a result of the PT -A40 wide scanner mirrors as opposed to buffo's PT-40's.

    Omar mentioned in an e-mail this morning that the green should have a spot size on the wall at 10 meters of 12 millimeters. That got me thinking and since I was going to have to take it out of the case anyway, I pulled the head off the base plate and flipped it upside down on the projector lid and fired it up, measuring exactly 10 meters from the wall.

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    Using my (standard) ruler, I got a rectangle of about 1/2 inch by about 5/8th of an inch at that distance (or 12.7mm x 15.875mm) There was an awful lot of speckle in a rectangular shape extending several inches around it.

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    I also decided to pull the blue as well just as a comparison. It too was a rectangle but about only .125 inch x .5 inch or so (3.175mm x 12.7mm)

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    Here they are from a distance:

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    And the blue a little more close up.

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    So... it still seems to me that the 520 green is considerably larger than it should be and, I'm wondering a little about the 462 blue although, I suspect it's probably ok. I just don't have any sort of reference to compare it to so I know exactly what I should be looking for.

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    I think the scanner may be the problem. If all the flat optics are of a good quality then the green coming out of the module should not get larger through the scanner. How could it? If you multiply the size of your green spot by the ratio of the 10M test to the first 13.716M test then you should not see anything like 41.27mm even if that represents the larger 5/8" axis. At most, it should be about 22mm thick. The blue makes sense to me. That kind of asymmetry and the super duper low divergence in the one axis is typical of these diodes when uncorrected. I am surprised by the green. Based on DTR's images of the 520 diodes, I thought they would behave very similarly to the 445's (or 462's) only a little bit better.

    So, based on what Omar has said, your green is actually performing close to what he predicted: 12 x12 @10M, but the beam coming out of the projector is not even close. And, your blue is also seeing a big deterioration after the module. If you project a grid with horizontal and vertical lines only in blue you will see the effect of the asymmetrical, rectangular beam in the line thickness. This is normal, but you should see a nice 12mm line in one axis and a "killer" 3mm line in the orthogonal line. But, I bet you won't!

    One other thought. The red seems less affected. What is the order of the blending of the beams? Are the green and blue seeing optics that the red is not?

  9. #19
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    The order in the projector is green first, then red, then blue. The green hits a 90 degree bounce mirror and then combines with the red's dichro and then combines through the blues dichro. The white beam then takes a 90 degree bounce and into the scanner mirrors.

    I'll try the blue grid experiment when I get to work tomorrow. The projector is set up there.

  10. #20
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    Brad, my green (520nm) in my Pluto II looked just like yours. The blue (462nm) was similar.

    I removed the custom correction lenses and G2 lens from the green and installed a 2 element lens. I lost a couple hundred mw but the dot became very clean and symmetric.

    In the blue, I took out the prisms and G2 and installed the same 2 element lens and the dot was clean. I did have to angle the base in the projector since the blue diode mount was offset, and I had to keep the module cover off.

    It looks great now, but after the scanners I am only getting about 2W which is acceptable for me.

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