# large prism in front of spotlight = rainbow beam?



## redberet (Mar 26, 2015)

If you put a large prism in front of a spotlight beam, will you get a gradient beam with the colors of the rainbow?


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## lucca brassi (Mar 26, 2015)

you will get specter of (MH - metal halide lamp) or halogen bulb - gas composition ( so not entire rainbow but specter )

in that way works spectrometers . you have source lamp , then you filter with prism desired wavelength out of specter and then you guide that beam through sample you want to research .

same thing on research of universe - stars ; star light (or sun) you get from telescope through prism and then you get specific spectre ( rainbow ) of elements that burns on sun surface.


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## degarb (Feb 15, 2017)

I have been wondering what practical ways of doing this. Practical means to me, a small cheap, durable, lightweight device that can be thrown into a book bag and toted to jobs. . Maybe a prism held in front of smart phone camera, manual white balance snapshot the rainbow and compare to ideal light of same cct. 

No luck for last two days googling. White swirl prism photography, cereal box, and 700 dollar spectrometry.


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## FRITZHID (Feb 15, 2017)

Diffraction grating won't work for ya?


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## degarb (Feb 15, 2017)

FRITZHID said:


> Diffraction grating won't work for ya?









https://flic.kr/p/QSCVPw








I see a $20 film. Yes looking for something tangible to buy. Above is a mmish slit in a box with CD inside. Will need to find a manual white balance app. . This will only work with flashlights I own. 


BTW, metal halides only come alive above 600 watts. . I don't see a 1000watt mh on your flashlight hit list.


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## degarb (Feb 15, 2017)

My CD in a box tests, aren't really showing me anything yet. A 2012 xml 6500 Kelvin xml rainbow look identical to my 2016 xpl 4300 Kelvin led.

Also, incredibly hard to get light angled and distance consistent.


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## degarb (Feb 15, 2017)

Vs.


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## degarb (Feb 15, 2017)

An album, comparing xml, xpl, xpe, from the Flickr App:
https://flic.kr/s/aHskRcMHn7


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## degarb (Feb 15, 2017)

https://youtu.be/9udYi7exojk


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## degarb (Feb 15, 2017)

FRITZHID said:


> Diffraction grating won't work for ya?



Been trying to find some youtube demonstration of a tool bases on diffraction grating. Most are mind bending, but useless. 

This one, blows my mind, as it is a must see:
https://youtu.be/A9tKncAdlHQ


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## degarb (Feb 16, 2017)

After hundreds of dead ends, found https://youtu.be/kx5R-3iakOw

Haven't found more than one source, $20.


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## degarb (Feb 17, 2017)

FRITZHID said:


> Diffraction grating won't work for ya?



What resolution film should I be looking to buy? Probably want something I can photograph and document.

https://www.edmundoptics.com/optics/gratings/holographic-diffraction-grating-film/54509/

I cannot get info on this stuff.


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## FRITZHID (Feb 17, 2017)

That I'm not sure of, you'd have to experiment.


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## degarb (Feb 17, 2017)

FRITZHID said:


> That I'm not sure of, you'd have to experiment.




https://www.youtube.com/watch?v=ZowYVDQDDZ4

1000 per mm. Unfortunately, this is only iphone. Not going out soon to buy an iphone.


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## FRITZHID (Feb 17, 2017)

1000/mm is what i used to take this pic using my samsung


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## degarb (Feb 17, 2017)

FRITZHID said:


> 1000/mm is what i used to take this pic using my samsung




Now this is what I am talking about! So, you just put the film over (or how far in front?) the camera lens, point at the light and shoot? Could you do several lights, for comparison?

What light is this?


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## FRITZHID (Feb 17, 2017)

It's trial and error. Took 3 or 4 tries till I got it where I wanted it.

That's not a light, that's the spectrum from my HeNe laser tube.


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## degarb (Feb 17, 2017)

When you have a chance, post some other lights, please.


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## degarb (Feb 18, 2017)

Found another youtube video, 
https://youtu.be/fl42pnUbCCA

They use the clear part of a recordable CD for the diffraction grating film. Is this even possible? 

Then, why not just buy a 3 foot section of black abs tubing, and cut it to 12 inches ? 

I wonder too, if you also need this foot long chamber and slit, even with diffraction grating film?


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## FRITZHID (Feb 18, 2017)

correct.
i just hold the grating about 6" from camera lens, then tilt/move around till it's where i want it and then shoot. i use no tubes/slits. lol

i'll get some more shots once i get more unpacked from my move. most of my lights are still in the garage.


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## degarb (Feb 18, 2017)

FRITZHID said:


> correct.
> i just hold the grating about 6" from camera lens, then tilt/move around till it's where i want it and then shoot. i use no tubes/slits. lol
> 
> i'll get some more shots once i get more unpacked from my move. most of my lights are still in the garage.



What are the dimensions preferable for this film, using your technique? Seems like you need a frame of some invention, dimension. Probably cardboard, glued Popsicle sticks, paint stir sticks, or pictures frame? 

Without a frame, you would need a third hand to operate the camera, or tripod - too restrictive.


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## FRITZHID (Feb 18, 2017)

like i said, i just hold the camera in one hand (cell camera) and the film in the other and aim, then shoot. it's really that simple for me.


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## degarb (Feb 18, 2017)

Ok. I also may ask how the quality of the 1000 line grating film spectrum compares to the CD techniques?


I found the simplest construction here, 
https://youtu.be/YStZk2zANvk

I knew there had to be uses for these tubes, beyond hamster toys.

The toilet roll tube is shorter than most designs. To me, shorter is preferable for storage, portability, durability, black paint. No one addresses length benefits. Pringle can, comet can, plumbing tubing of various diameter. So why not half inch tubing? 

This one clarifies black interior advantages, which seems minimal, https://youtu.be/ZJcl392f8ew


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## FRITZHID (Feb 18, 2017)

much clearer photos thru the film.


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## degarb (Feb 18, 2017)

FRITZHID said:


> much clearer photos thru the film.



Do you mean, much clearer photos through the film than a CD grating, or, much clearer photos through the film with inside of tube painted black?

Since your aren't using a tube I will assume you mean the film is clearer than a CD grating.

I am still unsure of how wide and long to order, of the 1000 lines. I would assume 3 to 5 properly dimensioned pieces would last a few decades, stored in basement.


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## FRITZHID (Feb 18, 2017)

correct, film vs. cd


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## degarb (Feb 18, 2017)

How big of a film slide do you recommend? . 3 by 5, 2 by 2 inch?


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## FRITZHID (Feb 18, 2017)

this is what i use


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## degarb (Feb 18, 2017)

FRITZHID said:


> this is what i use



https://www.rainbowsymphonystore.com/products/diffraction-slides-1000-line-mm

Unfortunately, they don't sell less than 50 slides at a time.


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## FRITZHID (Feb 18, 2017)

i think thats what i'd bought a while ago. it was less than $10.


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## degarb (Feb 19, 2017)

FRITZHID said:


> i think thats what i'd bought a while ago. it was less than $10.



How many fid you get? Amazon has one for $4, with many buyers saying theirs got damaged in shipping. Maybe 3 for $10. Then plenty for $20.

As I am unsure of the practical value, my gut wants three for $5, feeling one for $4 is risky. 

Made one last night from a paper towel roll, duct tape, recordable CD, yogurt cup, and black spray paint. . All the leds in my housr look full spectrum. The 6500 Kelvin are heavy in the yellow and green. Obviously, confirmation of bands or spikes on the metal halide, though it too was full spectrum, with stronger red than I expected. This was my 400w warmish probe start....the resolution, lack of tools, make the CD sub useful for evaluation of leds. . Merely confirmation that leds and mh is better than florescent.


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## FRITZHID (Feb 19, 2017)

look on eBay


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## FRITZHID (Feb 23, 2017)

here's some readily avail spectras...

Merc w/phosphor





pure xenon





incan



 

Ol school floro






Warm white GE Stick






Nichia 219b






Cree warm white XML2


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## degarb (Feb 24, 2017)

FRITZHID said:


> here's some readily avail spectras...
> 
> Merc w/phosphor
> 
> ...






Thanks, Fritz.!!!!!!!! 

That post does tell me a great deal, about where my CD-R tube is by comparison. Still we need a side by side shot of the same light, by same person, with the film vs. the cdR. The diffraction grating film is better defined, but perhaps, not light years ahead of the CD-R:









These are my images of my 4000K metal halide 400watt probe start, and a 4watt China direct filament circa 2015 purchase. 

I took a paper towel cardboard center, duct taped a round yogurt container onto one end, wallpaper bladed a mm slit in bottom (or used old solder iron), tightened up slit with duct tape on either side, duct tape a quarter blank CD on opposite end after pealing off its metal film by exacto knife around edges and duct tape pulling off metal film. Probably, I should melt groove or carve CD before scissoring of a CD R quarter. DVD R failed for me, had to use the recommended cdR on my second try. Duct taped outside for sturdiness and make inside darker. I did use black spray paint on yogurt, not tube, not sure if needed... I built another from a Pringle can, but don't think it long enough to get the definition. 

Now, your diffraction grating film bands are a more defined, probably less work getting the picture. The 219 and xml are beautiful. Some of your geometry is very interesting, and I would like to know more. The defined bands in the florescent are spectacular. 

So far, have not looked up lines per mm on the cdR spec.


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## degarb (Feb 24, 2017)

http://www.inpharmix.com/jps/CD_spectro.html


Looks like a CD is 600 lines per mm, your diffraction grating film is 1000 lines per mm, a DVD is 1300ish. I am guessing the dvd throws the spectrum too far off to the sides to see in a tube.

Probably more clarity with the film, due to thinness. Maybe the lines are less 3 dimensional, too. Also, 1000 is nearly 2x 600. 

Gonna have to try the dvd again. This time using the Pringle can, or Pringle plus pcv for length.


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## degarb (Feb 24, 2017)

This is a CFL CD spectrum. Definitely needs more resolution to evaluate, beyond:"Yeah, the CFL looks a tad more banded than the metal halide. And, spectrometry of the led looks continuous and not that different than the sun or Incan, regale ss of the led temp. " I still am holding out for 3 slides for $5,shipped. Any computer software to evaluate the spectrometry should be in html, not iPhone or dos. 

My phone is reading 3000 Kelvin for the CFL, 4500 Kelvin for the metal halide, 6500 for my 500 watt metal halide, which is the sales specifications.


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