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Full Spectrum and Infrared Photography

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Re: Full Spectrum and Infrared Photography

#11

Post by dheera »

asdff wrote: post #6
NoiseBert69 wrote: post #5

You’re considering whether it would be possible - and perhaps quite elegant - to use an XY‑scanner to raster‑scan the end of an optical fiber across a prism, disperse the light, and then capture the resulting spectrum with a CCD line sensor. With that setup, each pixel on the line sensor would effectively record the full spectral content of the light at that scanned position, all in a single acquisition.

A problem for multispectral imagery (even within visible rgb), is that the wavelengths of light are different so the lens cannot be in focus for all spectrum at once. I have tested this out with a few of my slr lenses. If you have blue channel perfectly in focus, red isn't just a little out of focus, it is actually noticeably way out.

I've had this problem as well, but it's just due to optical properties of the lens and extremely consistent from image to image, so you can calibrate and correct for it as long as you focus each wavelength and collect data separately.

Re: Full Spectrum and Infrared Photography

#12

Post by tomtom1337 »

NoiseBert69 wrote: post #5

You’re considering whether it would be possible - and perhaps quite elegant - to use an XY‑scanner to raster‑scan the end of an optical fiber across a prism, disperse the light, and then capture the resulting spectrum with a CCD line sensor. With that setup, each pixel on the line sensor would effectively record the full spectral content of the light at that scanned position, all in a single acquisition.

You could probably use just an X-scanner, and instead of a CCD line sensor, use a regular 2D image sensor if you used a "1 pixel wide" slit aperture to crop the image perpendicularly to the direction that the prism disperses the light. So instead of a single pixel being dispersed, you disperse a line.

You would reduce the time required by the root of the number of pixels you want (assuming a square image).

(This is what we do in momentum-resolved electron energy loss spectroscopy. In that situation we have electromagnetic lenses that focus the electrons that have been dispersed, so we don't have as bad a chromatic aberration problem as the other response mentions).

I would love to see e.g. a butterfly image with a slider that I could drag to choose the wavelength shown!!

Re: Full Spectrum and Infrared Photography

#13

Post by mncharity »

IAmBroom wrote: post #4
fraywing wrote: post #2

This is really cool -- pedantically, I've always thought "full spectrum" is actually misleading from a traditional photographic sense. Like IR + visible light + UV != full spectrum. I'd love to see post-processed imagery of every-day life through an extended view of broader EM energy (similar to astrophotography)... like what does a city scene look like with x-rays and microwaves included? Side note: have always love…

You'd obviously have to use false-color, as most modern astronomy pictures do (even the ones that use visible tend to pump the saturation UP!). However, the amount of light from the sun drops off exponentially away from the peak at green-blue (yellow-green, after atmospheric filtering). You'd also have to really fake the dynamic range a lot to get it to look any different from IR+Vis+NUV. (If there was 0.001% as much…

I like distinguishing "light" (physical world) from "color" (species-specific biology). Sunbeam blue light is already less intense than NIR-I, but human bio juices the blue. Most humans are bright-light trichromats and low-light monochromats. Rod sensitivity is 3 orders of magnitude up, with single-ish photon sensitivity. Some amphibians have an extra rod type, for low-light bichromaticity. Some deep-sea fish are bright mono and dark lotschromats (12+ rod opsins). So why not imagine seeing the world with a triple (or more) of short-wavelength super-rods, a few orders of magnitude more sensitive still, with whatever curves seem fun? Perhaps curves naturally selected for by "makes intriguing images of the world for social media"...

Re: Full Spectrum and Infrared Photography

#14

Post by miladyincontrol »

lytfyre wrote: post #9

>Whenever shooting a subject with a mixture of visible and infrared light, it becomes readily apparent that infrared light focuses differently from visible light. For many subjects, this can mean having to choose between crisp visible contours and an odd pink glow, or blurred edges with some unusual pink features inside. Some things never look sharp no matter where you move the focus. The extent of this effect is ver…

Superachromat is the term you're looking for in terms of lenses corrected throughout IR to UV. They're not actually that expensive if you know where to look, I got my Zeiss 250mm supeachromat for about $500 from a Japanese seller. Works a treat for full spectrum film work especially on a system that lets you swap between film backs, if not for the woeful cost of film these days.

Re: Full Spectrum and Infrared Photography

#15

Post by _Microft »

fraywing wrote: post #2

This is really cool -- pedantically, I've always thought "full spectrum" is actually misleading from a traditional photographic sense. Like IR + visible light + UV != full spectrum. I'd love to see post-processed imagery of every-day life through an extended view of broader EM energy (similar to astrophotography)... like what does a city scene look like with x-rays and microwaves included? Side note: have always love…

By this measure, there is no "full spectrum" photography ever.

Re: Full Spectrum and Infrared Photography

#17

Post by NoiseBert69 »

tomtom1337 wrote: post #12
NoiseBert69 wrote: post #5

You’re considering whether it would be possible - and perhaps quite elegant - to use an XY‑scanner to raster‑scan the end of an optical fiber across a prism, disperse the light, and then capture the resulting spectrum with a CCD line sensor. With that setup, each pixel on the line sensor would effectively record the full spectral content of the light at that scanned position, all in a single acquisition.

You could probably use just an X-scanner, and instead of a CCD line sensor, use a regular 2D image sensor if you used a "1 pixel wide" slit aperture to crop the image perpendicularly to the direction that the prism disperses the light. So instead of a single pixel being dispersed, you disperse a line. You would reduce the time required by the root of the number of pixels you want (assuming a square image). (This is w…

Very nice idea! That makes it much easier!

Re: Full Spectrum and Infrared Photography

#18

Post by asdff »

tomtom1337 wrote: post #7
asdff wrote: post #6

Earlier quoted context omitted.

A problem for multispectral imagery (even within visible rgb), is that the wavelengths of light are different so the lens cannot be in focus for all spectrum at once. I have tested this out with a few of my slr lenses. If you have blue channel perfectly in focus, red isn't just a little out of focus, it is actually noticeably way out.

This is called chromatic aberration, for those who are intrigued. Given that regular phone cameras have sensors that detect RGB, I wonder if one could notice improved image sharpness if one had three camera lenses (and used single-color sensors) next to one another laterally, with a color filter for R, G and B for each one respectively. So that the camera could focus perfectly for each wavelength.

Next issue would be the perspective distortion in the merged image

Re: Full Spectrum and Infrared Photography

#19

Post by asdff »

dheera wrote: post #11
asdff wrote: post #6

Earlier quoted context omitted.

A problem for multispectral imagery (even within visible rgb), is that the wavelengths of light are different so the lens cannot be in focus for all spectrum at once. I have tested this out with a few of my slr lenses. If you have blue channel perfectly in focus, red isn't just a little out of focus, it is actually noticeably way out.

I've had this problem as well, but it's just due to optical properties of the lens and extremely consistent from image to image, so you can calibrate and correct for it as long as you focus each wavelength and collect data separately.

I don't think you can property calibrate for it unless you also move the camera to compensate for focus breathing. I'm not sure if that would fully account for it either. That being said these things are only very noticeable pixel peeping.

Re: Full Spectrum and Infrared Photography

#20

Post by JKCalhoun »

I like the idea of using the IR, where it shows a greater degree of contrast, to act as a "contrast mask" on the visible light image.

I'm thinking of the beautiful cloud detail in the one IR shot where the visible light photo had lost all of that. Seems like some compositing (sort of like HDR) you could try to pull in the best of both worlds.

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