>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 very lens dependent. It also occurs in different colours of visible light too, depending on how well the lens design accounts for it. Optically, the term is "Chromatic Aberration" - lens designers try and account for it in the visible spectrum with optical design and lens coatings, and modern designs are generally extremely well corrected in the visible spectrum. _Usually_ designers aren't worried about the design correctly handing convergence into IR and UV, so how well designs focus them to the same point as the visible spectrum is hit or miss. There's specialist lenses out there that are designed specifically for wide spectrum apochromatism, but they tend to be special purpose and very expensive - especially if they handle UV.

The author mentions it at the bottom of the post as something they're interested in trying out, but I've found it very fun to play with dual bandpass filters - they pass a part of the Visible Spectrum + IR, which creates some interesting options in editing for visual display. There's an example in this set I shot with different filters - https://www.reddit.com/r/infraredphotography/comments/1dnki0...

Related project: I shot a lot of landscapes in Iceland using a thermal (long wave IR) camera to show geologic phenomena in action. This involved stitching together a lot of (narrow FOV) thermal images and overlaying it on top of visible camera images for context.

https://petapixel.com/2019/07/13/shooting-high-res-thermal-p...

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 loved this image https://imgur.com/NZjWfWT of rainbows with UV and IR visible.

One thing I've wondered about is IR fluorescence photography.

I've seen some examples in document forensics where a page that looks blank (or at least the ink is unrecognizably smudged) because of water exposure is completely legible with an infrared photo illuminated by UV.

I suspect there must be a hidden world only visible in IR and UV (and long-wave IR, e.g. "thermal").

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.

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.

Looks like grainydays on youtube can finally stop chugging flaming hot mountain dew everyday in the hopes that Kodak will bring back Aerochrome.

https://www.youtube.com/watch?v=v5KBQd_DkQw

This is super cool, I want one now

Author here. I agree with you, "full spectrum" is a generous marketing phrase for what might more accurately be called _extended_ spectrum.

People way smarter than me have been able to achieve DIY spatial imaging with x-rays via compressed sensing [1] and with microwaves via phased arrays [2].

Optical wavelengths seem to be at a sweet spot of good angular resolution, varied natural sources, and harmless to humans.

[1] https://www.youtube.com/watch?v=EuVgGrun1V0

[2] https://www.youtube.com/watch?v=sXwDrcd1t-E

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 x-ray light as there is, say, red light, DNA could only exist in the lightless depths of the ocean.)

So, it would look like an IR+Vis photo (light falls off pretty fast in the UV, too), except the ones you've seen oversell the IR.

So it would look like a Vis-light photo, with slightly shinier objects in it.

Sorry.

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

Playing with a hyper-spectral imager makes you rethink how we see things. I've talked about this before, but human vision essentially "low resolution" on the spectral bands. Using an HSI that "sees" in 4nm spectral slices from 350-1000nm is really interesting (Cubert Ultris X20 Plus). There's so much spectral information that we just totally miss. I really wish the equipment for capturing images at these higher spectral resolutions wasn't so expensive so we could see people experimenting with them on a large scale. The one I got to work with was more than a nice SUV and that's cheap in the space. The ones we looked at from Headwall that did something like 400-2500nm started at $250k. Those weren't even full-frame imagers like the Ultris, they were line scanning imagers. That massive cost jump was down to the fact that from ~1050nm+ you need much different hardware to capture spectral data.

If anyone is interested in some technical aspects of the "full frame" HSI I worked with, it's quite interesting. It had a 20MP Monochromatic Sensor that captured single-band 12-bit data behind an array of lenses that split the incoming spectral range (350-100nm) into 164 individual 4nm wide bands of light that hit 410x410px squares on the sensor. The sensor can capture from 350-1100, but the QE drops of really fast past about 850nm and the product limited the upper range to 1000nm. I'm sure I munged something there, but you should get the general idea. I highly recommend researching the space of HSI, it's fascinating.

Last thing to point out, when working with an HSI like this, one thing you can do is capture a "spectral fingerprint". Since you've gone from three bands on spectral intensity information to, in our case, 164 bands you have the ability to turn that high-density spectral data for each pixel into essentially a line graph. Using that information you can do matching against a database of known spectral fingerprints and identify materials and material properties really well. In the multi-spectra world you'll see this capability used to identify crop health. In the hyperspectral world you can identify so much more. For instance, it can see skin anomalies that aren't visible to the human eye. You can identify specific minerals in a picture of a bunch of rocks (you need up into the 2500nm range for this though). You can easily spot foreign objects on a conveyor of food items. Overall, it's a long list of capabilities and I'm certain there are many more uses we could discover if the imagers were cheaper. And if you are into the wider ML world (not just focused on LLMs I mean), you'll see ML Classification Models being trained on these spectral fingerprints as well.

Anyway, the "full-spectrum" is fascinating, especially when you are able to slice it thin.

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!!

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.