Light Normalization

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Yianni-VJ
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Light Normalization

Post#1 » Mon Nov 24, 2014 5:39 pm

I understand that to achieve equal exposure across the build area we need to print an array of pillars and by measuring their thickness, determine where to move the hot spot.

I wonder if there could be another way:
The following is a photo, taken from above, of the projector showing a solid black desktop on white paper.
It is clearly visible that the light is weaker on the bottom right side.
The paper's fibers are also visible, which makes the material inappropriate, a different filter media is needed.

Could it be possible to extract information from a properly taken photo, and use it on a software level to achieve a uniform light distribution?

I am not versed in programming, I am just putting the idea out there, in case someone finds it useful.
Please share any thoughts you might have.

Thanks !
Yianni




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mikej
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Light Normalization

Post#2 » Tue Nov 25, 2014 12:56 am

An interesting idea! We would have to assume that the camera is doing a good job replicating the actual light, but if that's the case we should be able to do something along these lines. I'll put it on my TODO list of things to work on.
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Robert Howle
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Light Normalization

Post#3 » Tue Nov 25, 2014 5:42 am

Anyway to incorporate light sensitive paper. Could put model of solid thin block covering selected build area, expose a coulple of layers, develop the "film".

Robert
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Yianni-VJ
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Light Normalization

Post#4 » Tue Nov 25, 2014 7:59 am

Sorry we cannot do that Robert, the first layers are not equal thickness.
But your idea is very good, a nice white, thin, almost opaque piece of plastic would work great I think,

For a test like this to work we need to use same hardware and specs.
Here is another idea: a custom made iPhone holder that mounts on the gold bracket.
We jog with the Z axis and shoot in HDR mode.
A programmer could introduce a Z offset value that works with iPhone's Macro capability.
Personally I hate iPhones, but everybody has one these days.... I will have to borrow...

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Robert Howle
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Light Normalization

Post#5 » Tue Nov 25, 2014 8:38 am

How about a test mode option in "calibration". Created (created by Mike and in software) with model snapped to floor one slice thick (slice thickness won't matter because just want image projected.. This is with no resin in vat, just photo paper in vat (like when u do grid calibration) over the window. Projector stays on for set time to get paper to react then be developed (would give u reference doc). After all, the thing we need to know is light distribution of the projected image (this would cover entire build area for resolution chosen. Maybe i'm not understanding your idea, also could be missing something important on my end, as i am no techy.


Me too, I'm a samsung 4 user. Really don't like Apple's stuff.

Robert Howle
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Yianni-VJ
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Light Normalization

Post#6 » Tue Nov 25, 2014 9:11 am

I think this suggestion is great!
It relies on analog methods of photography, and there are no camera lens interfering with result.
To do this we need:
- Wide format of camera film. (do they still make that?)
- A filter that will allow enough light to sensitize the film, but not enough to burn it...
[s]- A shutter to control the exposure times. [/s]
- A photo lab to develop the film.
- A lot of trial and error to produce settings that everyone can use.
It is a elaborate, but in principal it would work better than a digital camera's CMOS.

EDIT: Scratch the shutter!
We have one on-board, that works great :)

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Robert Howle
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Light Normalization

Post#7 » Tue Nov 25, 2014 9:20 am

There has to be a way to treat some paper chemically, let it dry in a dark place, and just expose it put it in a dark place and let it develop. Will do a little research.

Robert
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Metalcaster
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Light Normalization

Post#8 » Tue Nov 25, 2014 12:30 pm

Wonder how the new solidator is doing it? They claim no pdms and they show 8 huge eifel towers growing at once using a dlp projector on kickstarter. Maybe there is some form of light diffusion they are using?

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Yianni-VJ
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Light Normalization

Post#9 » Tue Nov 25, 2014 6:37 pm

Well, we where discussing about how to achieve equal brightness, not how to replace PDMS, but since you asked, this is their patent https://www.google.com/patents/DE202013103446U1?cl=en&dq=%22tangible+engineering%22&hl=en&sa=X&ei=w9XBUv3DC8TsoATKnoDgCA&ved=0CEEQ6AEwAQ

As for their big envelope, the solidator works in lower resolution to print that large.

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Eddie J
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Light Normalization

Post#10 » Tue Nov 25, 2014 11:05 pm

Lets go back in time to victorian photography. :D use silver nitrate paper which changes colour exposed to light. Then use this an an alpha mask to adjust the projector brightness accordingly.
https://www.youtube.com/watch?v=GNp-V3viRS8

I mentioned this before a while back, i owned a Miicraft printer and this uses a mask on the projector in the same fashion.

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Yianni-VJ
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Light Normalization

Post#11 » Wed Nov 26, 2014 3:26 am

Wow Eddie, this is exactly what Robert suggested !
I remember we talked about Miicraft's alpha mask, but we did not went over on how they produced it.
Do you think they used a similar technique?

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Eddie J
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Re: Light Normalization

Post#12 » Tue Dec 16, 2014 3:19 am

Yea could be produced this way. Seems easier than sampling the light with digital methods.

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tim.yoshi
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Re: Light Normalization

Post#13 » Tue Dec 16, 2014 12:59 pm

Okay, but I'll mention once again my general thought - to what exact wavelenght this method is sensitive? If it's about 500-800 then it will be completely useless!
Never forget that we are dealing with full spectrum light source! If it would be narrow spectrum say 265 UV LED, then such a method could be awesome.
In our exact case (B9 printer with B9R resin) we need to know not only light intensity but also a wavelenght for that "map". Moreover I expect such a intensity distribution to be different acros the different wavelenghts.
If we are talking about B9R resin then 350-550 nm is of our interest, if others like MJR, FTD and so on, then 300-450 nm.

I can't see any better light mask testing method then one which we "got under our nose" (local idiom here - means something that is close, near, always on the view, another words - hidden on the light). The photopolymers themself! They got perfect spectral response to... their own spectral response! :) One could print array of pillars with slightly lowered settings and see where he have lower and higher power IN THE DESIRED SPECTRUM of resin absorbance. But then we need on the software level to adjust accordingly. Now we have "hot spot" method. That is cool, but possbily something like dot matrix could be better, more intuitive and easier.
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Yianni-VJ
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Re: Light Normalization

Post#14 » Tue Dec 16, 2014 3:09 pm

Tim, I cant talk based on scientific facts, but I am under the impression that when a lamp gives out a pattern based on its individual geometry, a fingerprint if we might call it, while its intensity will vary, its wavelength distribution will be the same all over

Although, you may have a point if spherical aberration or other optical phenomena causes a prism effect.

I don't know if we could detect that with the spectrum analyzer gadget you proposed, I didn't receive it.
They mixed up the order and it was not delivered, I m trying to get in touch with them, but did not get a reply so far...

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Yianni-VJ
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Re: Light Normalization

Post#15 » Tue Dec 16, 2014 3:37 pm

Chromatic aberration
http://en.wikipedia.org/wiki/Chromatic_aberration,
This was the term I was trying to come by.
But this would be visible to the naked eye, no?

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tim.yoshi
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Re: Light Normalization

Post#16 » Wed Dec 17, 2014 4:04 am

I know what is aberration. I'm kind of hobby photographer too :)

I think more important is
a) vignetting effect of the lens,
b) hot spot of the lamp
c) uneven thickness and angle of placement of various coatings and filters which light should penetrate inside the case of projector (first UV filter on lamp, second (non-UV?) filter on case, color wheel etc) before it finally reaches PDMS. I noticed that when I fiddled with lamp, I had dramatically changed the hot spot position.
d) uneven dust distribution on all these filters and lenses
f) uneven degrading of coatings on filters and color wheel. I can't explain in other way fact that some projectors start to drop useful output to 20-50%. For example on mine - I had to bump MSM up to 2-3 to print semi-successfully in B9R.
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behold3d
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Re: Light Normalization

Post#17 » Thu Dec 18, 2014 9:34 am

has there been any success with the borafloat glass replacement instead of the lamp lenses?

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tim.yoshi
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Re: Light Normalization

Post#18 » Fri Dec 19, 2014 7:15 am

If you are asking me, more specifically regarding those 24x24 mm sqares of regular window glass I cut and installed in place of first (lamp) UV filter? Then yes, it just works. I still haven't disassembled it and haven't looked what cracked there (i heard it almost immediatelly after placement and turning it on). But it still works! I haven't noticed any degradation in models quality, nor uneven curing. All cures fast as it was without this glass (ok, maybe 5-10% more, but from 3-3.5 seconds it's around +0.3 seconds). I'm not printing to much, but maybe 3 times a week. So far 10+ prints - good.
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