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Amateur infrared? It sounds amazing if we could only buy a camera that detects it!


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No doubt more experienced imagers have thought about the poor quality of the typical blue subframe, and how the red subs always seem to have the highest contrast and lowest LP intrusion. And of course how the sky is blue in the daytime, and when objects in the far distance fade into the fog, they fade to blue.

I wondered recently: "Just how far into the IR does this effect hold true?" only to realise that if amataur IR cameras and filters were available, it could be a whole new world of possibility!

First off, not only would the sky be FAR more transparent, but the negative effects of seeing are actually reduced considerably! Just have a look at the comparisons avialble on this website with an unfortunately not astro friendly product: https://www.infinitioptics.com/technology/nir-near-infrared

And on top of that, hydrogen has THREE emission lines at 1.09~, 1.2~ and 1.8~ microns. Beyond what our full-spectrum CMOS cameras can see, but no doubt impressive and fascinating structures. And to make things better.... No light pollution outside of the visible light range either!

The closest I have found to amateur astronomy IR-capable cameras... Are professional IR-capable cameras... One of which is a 92x92mm sensor. Something tells me even if they would sell to us peasants, we wouldn't be able to afford any of them. https://www.teledyneimaging.com/en/aerospace-and-defense/products/sensors-overview/infrared-hgcdte-mct/

Of course we would suffer a penalty to our diffraction-limited seeing, as 2µ would be about 1/3 the optical resolution of 700nm. But for the new things and possibilities I think it would be a worthy sacrifice for those interested in what lay mere nanometers and microns beyond our reach!

What do you guys think? I feel we're missing out here.

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A lot of CMOS astro cameras are sensitive to infrared. Check out the specs of the ZWO ASI224MC, for instance. I have used mine to image planets in near infrared, with an IR-pass filter.

All DSLR cameras have an IR-cut filter, which some astro users are keen to remove...

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38 minutes ago, Cosmic Geoff said:

A lot of CMOS astro cameras are sensitive to infrared. Check out the specs of the ZWO ASI224MC, for instance. I have used mine to image planets in near infrared, with an IR-pass filter.

All DSLR cameras have an IR-cut filter, which some astro users are keen to remove...

Even the 224 only has 10% QE at 1µ, which is 1/3 the sensitivity it has at 900. Following that trend, by the time it is trying to capture light at 1.1 (the first IR hydrogen line) it would have 0.03% QE!

zwo_asi224mc_chart_1.jpg

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Silicon camera with long pass can work, are liked by solar and planetary images for giving crisper images and less instability, though you take a hit on the resolution. There are some long pass filters for planetary and methane imaging applications out there. Very interesting to see the QHY camera. If you can afford one then you could pay one of the numerous custom filter makers to knock up some narrowband filters for those “new” wavelengths. Glass refractive indices tend to be quite flat beyond the red, but reflective optics would probably be preferred… as long as not dielectric coated (you’d need to watch out for IR blocks and check the performance of any “AR” coatings as they’d likely not be away from the visible. For proper IR (think 10micron thermal) you can see the moon OK, but the lack of sensor resolution, atmospheric moisture and cost of optics makes it less interesting.

 

Peter

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Infra-red astronomy from the ground is tricky. Not only is the background sky very bright, most of the signal gets absorbed by water vapour in the atmosphere!

NIgelM

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Silicon sensors stop responding to wavelengths longer than 1100nm. This isn't that much of infrared (more like "200% red"). Some time ago Sony did release a different sensor that operates above 1000nm but the price is similar to a small house.

Also on longer wavelengths light can go through dust more easily, which is visible even with standard sensors (Ha filters vs PP742):

ir.jpg.8d12c6f563f35e3dcf42c339f816924e.jpg

 

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Remember that NASA’s IR imaging telescope pre JWST was airborne, to exclude most of atmospheric influences. Silicon devices could, in principle, detect wavelengths longer than 1 um, but internal losses increase with increasing wavelength.

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3 minutes ago, wimvb said:

Remember that NASA’s IR imaging telescope pre JWST was airborne, to exclude most of atmospheric influences.

Depends how long wavelength you want. 1100-1600 nm is often done from standard ground observatories.

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44 minutes ago, wimvb said:

Remember that NASA’s IR imaging telescope pre JWST was airborne, to exclude most of atmospheric influences. Silicon devices could, in principle, detect wavelengths longer than 1 um, but internal losses increase with increasing wavelength.

 

36 minutes ago, riklaunim said:

Depends how long wavelength you want. 1100-1600 nm is often done from standard ground observatories.

The VLT can capture up to 20µm, albeit in the middle of a desert and at great altitude haha.

 

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1 hour ago, pipnina said:

The VLT can capture up to 20µm, albeit in the middle of a desert and at great altitude haha.

They may very well use germanium based senors. Germanium has a smaller bandgap than silicon and can detect longer wavelengths.

2 hours ago, riklaunim said:

Depends how long wavelength you want. 1100-1600 nm is often done from standard ground observatories.

IR sensors require special cooling. Otherwise any heat signature can manifest itself as glow. The longer the wavelength, the lower the temperature. 20 um definitely requires cooling, with most likely liquid nitrogen.

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As someone else has mentioned, doing this at UK altitudes will be difficult due to water in the atmosphere. The UK used to have an infra red telescope in Hawaii, but that was at an altitude of 4.2 km to avoid this problem.

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1 hour ago, PeterW said:

The following link may help provide some info as to where it might be worth looking and where not. https://www.climate-policy-watcher.org/climate-dynamics/the-atmospheric-absorption-spectrum.html Although water absorbs a lot au can clearly see the moon with my 10micron thermal scope (resolution is too poor to see details).

 

Peter

What kind of thermal system do you have? Very cool to get images in UK skies at that wavelength!

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Low end Pulsar thermal spotter, the auto contrast function means the moon is an over exposed disk.. a clear sky is blank. It’s real power is in finding warm things after dark.

 

Peter

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