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Testing the Microvision SHOWWX and AXAA L1 Laser Pico Projectors

dsholz

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Re: Testing the Microvision SHOWWX Laser Pico Projector

Good news everyone! I'm going to have access to an AXAA L1 this upcoming week, and I intend to do a good side-by-side comparison. If anyone wants me to look at anything in particular, here's your chance to put in requests ahead of time :).
 

dsholz

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Re: Testing the Microvision SHOWWX Laser Pico Projector

Here's a quick write up for tonight. I'll elaborate and post more in the near future. Please post any questions you have, while I have access to both units.

Initial Impressions of AXAA L1: Although the AXAA L1 has a nice metal body, it immediately seems twice as heavy and twice as thick as the SHOWWX. This turns out to not be quite true when you add the metal VGA adapter to the SHOWWX, but if you plan on connecting this to your iPOD then there is no doubt which is the 'slimmer' device. It's very nice having a keypad on top to control the unit without a computer, however, the menu system is sloppy and unintuitive. Worst (to me), pressing any of the buttons produces a loud "ding!" button noise which I don't think can be disabled. One time, the OS even froze on me, and I was unable to restart the device (I had to wait for the battery to run out). The lasers instantly turn on, but the OS takes about 15 seconds to 'boot' up.




It's really nice how the L1 has all these extra ports on the side (and can plug directly into a PC for video output). To me, this was one of the huge downsides of the SHOWWX design.





You can see the lasers and some optics going inside through the vents.

Heat and Noise: The AXAA L1 has a tiny fan inside and a large number of vents. This seems to allow it to remain cooler than the SHOWWX with its metal VGA adapter (without the VGA adapter, the SHOWWX is much cooler). The fan isn't noisy at all, but it does produce 'some' noise, which you might notice when switching from a completely silent SHOWWX.

Accessories and Ports: The AXAA L1 comes with a USB thumb drive which can be plugged into the unit to access/transfer videos and photos, however, this feels somewhat unnecessary given the popularity of thumb drives these days.

General Comments on Image Quality: The AXAA L1 produces a smooth picture with no visible pixel borders in the image. The DLP chip produces a definite rainbow effect, but there is no other discernible frame refreshing (unlike the SHOWWX, which suffers from the same discomforts of any 60 Hz CRT monitor). To me personally, the rainbow effect on the L1 was less annoying than the 60 Hz raster scan refreshing on the SHOWWX, but I doubt either issue would bother most people.


Here's a picture of the L1 rainbow effect (made by moving my hand quickly through the projector beam), which comes from projecting the red, then green, then blue images separately. If you move your eyes fast, or move your hand in front of it, you can see the colors separate.

Color Quality: In displaying an RGB color gradient on both projectors at the same time, the SHOWWX appeared to produce more vivid hues, with the L1 having washed out reds, yellows, and purples (both had the same dark 445nm blue).



Image Brightness: Although the AXAA L1 is rated at 20 lumens and the SHOWWX is rated at 10, I did not see a major difference in brightness, although during the photo-shoot the microvision was looking brighter.



White Balance and Constrat: The SHOWWX produces much better whites than the L1. Both have good contrast, but you can definitely notice that the L1 cannot display absolute blacks, as the SHOWWX can (by turning off its lasers while scanning black areas).

Laser Characteristics: Surprisingly, the L1 is labled as a Class I device (where the SHOWWX is marked Class II). All of the different laser colors have the same polarization (unlike the perpendicular ones of the SHOWWX). It seemed like the Microvision might have a slightly stronger speckle effect (it "appears" as if it comes with the stronger hues, but I'm not sure what that means). I'll measure this speckle effect in MATLAB tomorrow evening.
 
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Things

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Very impressive writeups :)

Interesting how the SHOWWX is brighter, yet is supposedly 10 lumens less, but the L1 seems to have a larger image at that distance.

Cheers,
Dan
 

dsholz

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Things: I also thought the brightness difference might be due to the different image aspect ratios, but after running the numbers I'm not so sure.

The AXAA L1 has an aspect ratio of 800/600 = 1.3 and the SHOWWX has a aspect of 848/480 = 1.76. This means if I line them up so that each produces an image 1 meter wide, the L1's image will have a height of 1/1.3 = 0.7m while the SHOWWS's has a height of 1/1.76 = 0.58m. This would make the SHOWWX 'lumen density' 10 lumens /0.58 m^2 = 17.6 lumens/m^2 and the L1 20 lumens / 0.75 m ^2 = 26.6 lumens/m^2.

This means the L1 should still have a 26.6/17.6 = 1.5x lead over the SHOWWX when both images have the same width, but I don't quite see that here.
 
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dsholz

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Wow, not a lot of interest in the AXAA vs. SHOWWX comparison? I only have access to both projectors until the end of Friday, so if anyone has any questions (or anything you want me to test) please ask them as soon as you can.

I'll see about putting them both under a laser power meter and spectrometer, but those are the only other tests that I have planned.
 

AJ_Dual

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Can you take a fast enough exposure to catch the actual dots on the wall tracing out the scans instead of the entire video image?

I think that would be cool and enlightening as to how the projectors scan the image onto the screen/wall.

Also, since you're getting RGB ghosts out of a hand waved through the AAXA's projection, I'm thinking it must be like the Casio A130/A140 where it's using laser diodes as an illumination source and not directly painting with the beams like the Pico does.

That RGB effect is due to the color wheel generally and a direct laser illumination would not need it. It would also explain why the Pico has laser speckle constructive/destructive interference, but the AAXA does not.
 
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kiyoukan

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i know you had a couple of pics but could you make a beam show out of this?
I know its not powerfull but it seems very possible for it to work.
 

dsholz

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kiyoukan: I'll try to make some movies of the microvision making a beam show in a few days.

AJ: Yes, the AXAA uses a DLP chip just like the Casio. I would not say it does not have any speckle, it may be roughly equal to the Microvision's. I'll try to take some 1/4000 second pictures of both projectors, but it won't be super-interesting. For the Microvision you just see a scanline, and for the AXAA you'll just see darkened lines in the image from temporal dithering.
 

Atomist

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dsholz,

Thanks for testing these projectors! I'm quite fond of the ShowWX, or at least it's potential. I've found you can get rid of the speckle by attaching transducers to your projection surface. I used the following:

1. Dayton DAEX25 Sound Exciter
2. An amplifier or receiver to drive transducer (I used Dayton DTA-1 Class T amp)
3. audio source, I used a cheap $20 mp3 player, there's also this free signal generator that works great:

LF Generator

You can use a signal generator to output a sine wave, or Audacity sound editor to create a sine wave that can be played back on an mp3 player. Frequency range will vary, but 40hz-60hz seems to work well.

The 2 or more transducers are applied to back or front of your projection surface, which needs to be somewhat flexible. When the transducers move in and out, they will send ripples or waves throughout the projection surface. Because the angle and surface patterns of the projection surface will be constantly changing, individual photons within the beam strike different patterns, and the luminance is averaged out, and voila, speckle is minimized or even eliminated.

I don't have my showwx right now, but I'd like to try aiming the Showwx toward a mirror moving longitudinally (forward and back) and then directing that toward the projection surface. Similar principle as vibrating screen above, but the beam is moving instead of the screen. I've tested this by attaching a small mirror to the Dayton DAEX25 transducer @ 120hz-230hz reflecting a laser level and it seems to work. The only question is whether this will blur the image too much for sufficient speckle reduction.

Also, there is a new firmware for the Showwx that allows adjustment of laser bias. Unless your unit shipped with the new firmware, you may have noticed that displaying a star field that the green laser smears or trails between stars instead of fully shutting off for black. Also, signal levels between 5%-20% what should be a full screen of a solid color, are instead blocks or columns of shades of that color. If your interested you can email Microvision for the firmware or I'd be happy to just upload or email it to you.

Overall the ShowWX produces a very pleasing image once you get rid of the speckle. My only real complaint is that it needs to be brighter! 50 lumens minimum would be nice. Hopefully in the next year I'd like to experiment with either increasing the brightness of the lasers, coupling more powerful lasers via fiberoptic to ShowWX (and using the existing voltage driving the ShowWX's lasers as the input signal to be amplified) OR aligning several ShowWX with an X-CUBE prism (found in lcd projectors to converge R G B lcds) to increase the brightness.

Sorry for the long post!
 
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Atomist

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Also, the Axaa L1 uses an LCOS chip, basically reflective lcd. In this case same concept as color wheel & single chip DLP but with lasers and liquid crystals. LCOS is also known for it's high pixel density, producing a nice smooth image. LCOS is used primarily in home theater projectors but is very popular with pico projectors as well. JVC's version of LCOS is DILA, Sony's is SXRD. And according to rumors, Epson will be announcing their version of LCOS during CEDIA in September.
 

dsholz

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Atomist: Thanks for the great post. Your theory for eliminating speckle is very interesting and I would love to try it myself, but I don't have any transducer related equipment.

The image shouldn't be too blurred if your vibration amplitude is small. From what I understand, the speckle comes from the coherent nature of the laser light, and I'm not totally sure if a low amplitude vibration will vary the coherence enough to make a difference, but it may make the speckle pattern change so fast that your eye averages it together into looking like a lower amount of noise.

Please post the results of your experiment when you conduct it :).
 

hometon

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thanks for the great comparison tests on the 2 projectors, dsholz. Many of the LCoS and DLP projectors also claim more lumen brightness than Microvision's ShowWX. The panel type projectors (DLP/LCoS) require that the light source cover the whole chip evenly - then the pixels that require the color are allowed to be projected, while the others must deflect and absorb the waste light - which turns into heat. Some of the rejected light can leak, and can cause reduction in the contrast ratio. And it is difficult to evenly distribute the light evenly over the whole chip, which can cause the tunnel effect - brighter picture in the middle and dimmer at the edges.

Atomist: very innovative work on speckle reduction. I have read many patents/applications on speckle reduction (there are many), and one of them used this same technique - vibrating the display surface. Other techniques involve vibrating the scanning mirror but I don't think this will be possible for you. Would be great to see some photo's of your work. Mitsubishi laser TV has solved the problem - not sure what they do - they are rear projection and the interference patterns may not be propagated through to the other side.
 

cjyetman

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Re: Testing the Microvision SHOWWX Laser Pico Projector

Does anyone know why it warns against "invisible light"? I figure this thing should have a IR filter on it. Or is that just the standard labeling/warning?
Could it be because the "green" laser is actually a frequency doubled IR laser?
-cj
 

Canuke

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Looking at the last video posted by dsholz, I'm 99% sure that this display is interlaced, to the same spec as the old CRT's.

It makes sense for several reasons, not the least of which is that 60Hz 480i video, being the once-ubiquitous old NTSC standard, avails the manufacturer of a huge pool of existing silicon already tuned to that spec.
 

Atomist

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As dsholz already noted, the ShowWX does appear to be doing 480 progressive, but, it is shifting the scan lines to fill in the gaps. I've owned a CRT projector, and can say from experience that gaps between scan lines are visible with 480P at larger image sizes. However, I would rather have these small gaps between scan lines than for the scan lines to be moving around. Microvision's approach works great for still images, but when displaying video, the scan lines moving around can be very visible and distracting. This might work great at a higher refresh rate, but at 59.9hz it doesn't cut it. Hopefully next year's 720P model will have fixed scan lines; the vertical pixel gaps should be small enough to not be noticeable.
 

styrum

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I just checked Microvision site. SHOWWX is down to $449 as their "back to school" promotion!
 




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