Cameras for visible light abound, and there are specialized ones just for infrared, ultraviolet, x-ray, etc. But is there any camera (or optical equipment of some sort) which can tune to any frequency of the EMS?
If not, how do spectrograms (graphs?) work - there seems to be a way to take a linear continuous EMS reading. I imagine it’s not a huge leap to make it into an array and stick a lens on it?
It’s very difficult to find a material that is sensitive to all wavelengths. All detectors have ranges in which they work, and outside which they are not responsive. There are some detectors which respond to thermal effects that can be used over much broader ranges (thermopiles, many bolometers), but they tend to be slow in response, and even their range is limited.
So how do spectrographs exist? As you’d expect, they uswe multiple detectors. An individual spectrograph will work over a particular range, which overlaps with other spectrographs that work over different ranges.
It’s not only the detectors – the dispersive elements will only work over certain ranges, and optics themselves – lenses, windows, and mirrors – have ranges of operation. Vacuum ultraviolet spectrographs won’t even work unless the air has been evacuated from the optical path.
I’ve worked with spectrographs that worked over very broad ranges. At points in the operation, you had to wait while one set of optics was automatically switched out and another set switched in. At the other end of the automated scale, I’ve personally had to take gratings out of a spectrograph and replace them others so that I could look at a different spectral range.
There are such devices - called, unsurprisingly - imaging spectrographs. But you need to realise that if you are getting a spectrum for each pixel you are going to need a vastly more complex and compromised system. You are not going to get 10 megapixel resolution. You are also going to have to place pretty serious restraints on the spectral resolution. There isn’t going to be all that much light per pixel to spread out over a very high resolution sensor. As CalMeacham points out above, you can’t expect a singe sensor technology to work across a really wide range of wavelengths anyway. But if you stay within visual and near UV and IR it isn’t too bad, and you can continue to use CMOS or CCD sensors. But your basic image array is going to be replaced by something that can take each pixel and send it to a separate spectrograph - or at least scan the image. This then means you have temporal constraints on the image as well. So, astronomy and earth observation satellites are a good place to find them. So the concept is sound. What it is, is a pretty big technological leap to implement.
The WST uses a set of micro machined shutters to select a limited set of sources from the image plane to send to the spectrographs. So whilst not strictly an imaging spectrograph, it gets the job done.
I guess the thought experiment here is to basically take a series of photos of an object (or person, or scene), each photo in the series at a different frequency/wavelength, and then combine them into a video that shows what the object looks like gradually along the entire detectable spectrum.
If you’re going to be looking at things down in the microwave/radio end of the spectrum, you’re going to run into the diffraction limit if you actually want to build a “camera” capable of taking images. Basically, for a camera to create an image, it’s necessary that the size of any “aperture” the EM waves pass through be much greater in size than the wavelength of the light. For light, this isn’t an issue; for radio waves, with wavelengths of a meter or more, it would rapidly become problematic.
I guess radio telescopes have very large lenses? How do audio transmission radios work around this?
Audio is modulated onto the radio frequency carrier. In the simplest form amplitude modulation (AM) is used, and you simply vary the level of the radio frequency energy with the audio. You can do other things, like frequency modulation (FM) where the audio signal is used to change the actual frequency of the radio frequency energy a little bit.
There are radio signals that are so low that the actual frequency of the radiated energy gets close to the audible range. The Omega system used between 10 and 14kHz . High pitched, but audible. There was no possible directional antenna, the whole scale of the system was a single global system. In principle you could have made the entire system across the planet into a single directional antenna.
Audio transmission radios don’t care where the radiation are coming from. They’re not doing any focusing, so they don’t need “lenses”.
For something like a conventional AM radio station this is largely true. But there is, or at least has been, much more than this. In the extreme consider the Apollo astronauts ambling about on the moon. They had a direct to Earth radio link. It carried voice, data, and slow rate video. They used a small dish on the lunar surface, and the combined might of NASA’s deep space network to haul the signal out of the ether back on the Earth. Those antenne were highly directional, and needed to be. Their directionality came from a combination of their large size, and the very high frequencies used for the transmission. Before the advent of transcontinental fibre optic networks phone calls were carried on microwave links, and the countryside was dotted with towers that relayed the signals. The microwave dishes were highly directional, and again needed to be.
There is something similar called hyperspectral imaging where images are captured using a wide swath of EM frequencies. I seem to recall 256 separate bands are common but it’s been a while and im on my phone and can’t really look things up. Anyway, you can take a pixel that looks interesting and plot all 256 values for that pixel into a histogram and compare that with predetermined values to identify what is in the photo. In a hyperspectral satellite or aerial image of a forest, for example, pine trees will have a certain histogram that looks different than oak trees, so it becomes simple to map out different species of trees.
I work with hyperspectral cameras – they do, indeed, give the spectral data for each picture element in the scene, but they take fewer picture elements on account of that – you still need one detector element per wavelength bin, after all.
And any hyperspectral camera can only take data over the regioon where the detector array will respond and where the optics will work. There are hyperspectral cameras that operate in the visible/Near Infrared, Short Wave Infrared, Mid-Wave Infrared, and Long Wave Infrared, but no camera that covers all of those ranges AFAIK. And that’s not counting ultraviolet and x-ray regimes on one side or wavelengths longer than 12 microns on the other.
In general, you have what’s referred to as a “data cube” at each instant, with two dimensions of spatial information and one dimension of spectral information. Ideally, you’d like to get the full data cube, but in practice, usually all you can get is a bunch of planar slices through that cube. You can get good resolution within each planar slice, but you generally only have a small number of slices available. Depending on the design of your instrument, you can arrange your slices in all sorts of ways: For instance, you could take individual photographs through an assortment of narrow-pass filters, or you can take an image through a set of slit spectrographs.
Actually, it’s a hypercube, with cube slices through it, since you’ve also got the time dimension you can play with, by doing things like scanning a slit across what you’re looking at.
Hyperspectral was just something semi related that I thought may be interesting to the OP. The original question is no, there’s no single sensor or camera that can view many bands. But for the thought experiment, you could piece together a video using different instruments that cover much of the EM spectrum. Radio is iffy, but some weather radars use the 3–30 MHz HF band. They produce a picture of precipitation, we just normally look at it in top down slices. Making an image of an everyday object may be iffy. Airport security scanners and other radars use microwave. Infrared, visible, ultraviolet, and x-ray all have imaging devices. Gamma imaging is used in the medical field but I think only for imaging small localized areas of the body.
The downside is that we can only see in the visible light band, so all these imaging devices represent their images using that. UV and microwave imagery usually look like black and white photos, just with different details. Others may be in color, depending on how much data you get and how you want to present it.
Uh, I think I’m just getting farther from what the OP wants though.