thermal astrophotography?

[Ultrapurple]

Although it's some time since this topic was last live, I've finally come across the information about the telescope I used for my moon thermal images. It's a Celestron 'GoTo' (computer controlled) reflector of 650mm focal length and 130mm aperture, making it f/5. That helps explain why an uncooled sensor struggles with even a hot subject such as the moon - f/5 just isn't wide enough.

If I was using a cooled sensor, on the other hand, f/5 would be plenty wide enough for some very practical experiments on terrestrial subjects. Well, terrestrial subjects at a distance, anyway - all other things (sensor size) being equal, a man-size target would be the full height of the screen at a range of about 1000 feet and it would be great for thermal portraiture at about 200 feet.

650mm focal length on a Therm-App sensor is roughly the equivalent of a 3700mm lens on a 35mm full-frame camera.

[LesioQ]

I hope You're using some measures to reduce visible bandwidth when pointing the scope at the Sun, as most of Sun's emitted energy falls into this uninteresting to You emmision range.
Perhaps some foil for visual observations (either mass-tinted or two-side sputtered) can be used, as these reduce energy at the focal point some 1E4 times.
Then it's thermal range transmission may create the final image, without frying Your camera and surroundings. 

[Bill W]

The usual germanium optics / sensor window deal with visible / NIR quite well  .

Even with an f/1 lens in a normal thermal camera, pointing it at the sun is unlikely to be fatal to it.  You just get a mark that takes a bit of running (worst a day or two) to fade away, that is all.

Bill

[Vipitis]

But the temperature of a wife Aperture telescope looking into the sun without filters will be too high and can mess up your mirrors and coatings.

[Ultrapurple]

I've never deliberately tried to image the sun, but I have accidentally pointed my Therm-App in its direction on occasion. As Bill W says, there was a bit of a streak that took a little time to fade (hours), but that was all. I suspect it might be different if I deliberately left it staring at the sun on a tracking mount with large aperture optics.

The Pico 384 used in the Therm-App (and Pico 640 in the Pro) are rated by Ulis as sun-safe, but I'm not sure the same can be said of all thermal imagers. Somewhere deep in the back of my mind is the 'white-out' failure mode of the early, early pyroelectric vidicon-based fire TICs. I'm sure someone on here will know enough about the history of uncooled (and/or cooled) sensors to be able to say if there is a type that is particularly sensitive to overload. I know there are some imaging and non-imaging light-sensitive devices that can be catastrophically damaged by overloads such as looking at the sun (I'm looking at you, Mr Bean), but how far that extends to the last 40 years or so worth of thermal sensors I'm unqualified to judge.

[mahony]

Interesting that the ThermApp is showing marks after pointing it to the sun. As far as I have seen so far the TE-Q1 and also both Lepton3's that I have don't seem to show anything like that. Although I have to admit that in all cases I would not call it 'worst-case' scenarios because it was not the hottest summers day and around noon but quite a bit in the afternoon/evening usually.  And I am located around 48° north ... ;-)

[cdev]

At certain RF frequencies, you can image the galactic plane (the "Milky Way"), going across the sky (using a gain antenna) using any kind of directional mount that can scan it across the sky. (or the Earth's rotation, if you leave it stationary but pointing up) the resolution will be sharper the more gain the antenna has. At almost any frequency the Earth will show up as noise and the sky will have much less noise.  Radio astronomers use the quiet sky and a waveguide pointing up to evaluate low noise amplifiers.

[Vipitis]

Yeah, but is it possible to do dso in LWIR from the ground? Becuase the window for IR in our atmosphere is rather slim.

It is possible to do Planetary Lunar and Solar FIR astronomy from ground, even with consumer products.

[cdev]

Non thermography IR (infra-Red) cuts through haze during the daytime better than visible light, as shown by the dark skies and long distance views possible when using filters like my #87 wratten filter which to the naked eye in visible light appears pitch black. Satellite phtography of the Earth makes extensive use of it because ground features are visible even when haze obscures them in visible wavelengths.

[Ultrapurple]

Interesting that the ThermApp is showing marks after pointing it to the sun.

Yes, for a relatively short while. I scared myself quite badly when I used my first Therm-App to image a toaster: there was a significant after-image for some time (minutes to hours) but it ended up being none the worse for wear. Discussion on the Therm-App Users group suggested it was simply down to physically warming the device to an extent greater than the substrate could dissipate quickly; it sorted itself out and there were no lasting problems.



The sequence here shows the toaster elements very hot, then overloading the sensor, then remaining 'lit' when the heat source was switched off and, finally, what happened when the sensor was pointed away to a cool wall.

The sun issue was similar, except that it left a streak a few pixels wide that, again, faded with time.

[Ultrapurple]

I have done some work on near-IR (1100-800nm) using a Fujifilm Finepix IS Pro and I can confirm that the performance in haze etc is markedly better than visible light.

As far as longer wavelengths go, whilst the atmosphere does attenuate signals a lot, bear in mind that big, close, hot targets like the sun start out with an enormous intensity per square whatever above the atmosphere; even attenuation by (say) 60-100dB still leaves you with a lot to play with.

I am reminded about a local AM radio transmitter that had an ERP (power) of something like 500,000W. Local radio hams were having problems with the second and higher harmonics, which fell into ham frequencies. The site operators took the concerns seriously, checked everything out and confirmed that their filtering was actually rather better than required by law. However, they were still radiating a goodly fraction of a watt on the amateur bands - 60dB down on 500kW is still half a watt - hence the locals having difficulties. It was never resolved; there wasn't much the site operators could reasonably do and they were already cleaner than they needed to be. It's the same with the sun: even a lot of attenuation leaves a detectable amount.

[Bill W]

The Pico 384 used in the Therm-App (and Pico 640 in the Pro) are rated by Ulis as sun-safe, but I'm not sure the same can be said of all thermal imagers. Somewhere deep in the back of my mind is the 'white-out' failure mode of the early, early pyroelectric vidicon-based fire TICs. I'm sure someone on here will know enough about the history of uncooled (and/or cooled) sensors to be able to say if there is a type that is particularly sensitive to overload. I know there are some imaging and non-imaging light-sensitive devices that can be catastrophically damaged by overloads such as looking at the sun (I'm looking at you, Mr Bean), but how far that extends to the last 40 years or so worth of thermal sensors I'm unqualified to judge.

The ULIS sensors have been sun safe for a few years, before that you could do 'days' or even permanent changes to the pixels in gain and offset.  Once stable of course the camera could be recalibrated and the pixels either accepted and adjusted or declared dead and covered up.
Any of the thin film sensors are likely to be susceptible to some degree or another, I'd suspect an old BST would be immune as it is ceramic.  Can't remember trying though.  Where cameras have a shutter or iris though it will often be deliberately closed when the camera is turned off.

As for 'white out' on pyroelectric vidicons, that was an entirely different problem or two.  If you got enough energy in you could generate enough charge to turn the electron beam around and prevent readout, resulting in a runaway charge build up on the target.  The only fix was a power cycle.  If unlucky the charge might 'depole' the target (ferroelectric) which altered sensitivity.  This was easiest to do by sneaking up on a fire and suddenly exposing the camera to it, if approached normally the iris closed and did its' job.

The term has now been moved to a similar effect caused by poor image processing and with colour pictures is now 'red-out' where the fire is displayed as all one tone.

Bill

[Vipitis]

From what I remember of the flir eclipse coverage, it's possible to do with various camera types and flir themselves had multiple locations and cameras.
http://www.flir.com/home/news/details/?ID=86392
Some were filtered to specific wavelengths and in the Facebook comments of some videos they talk about he filters used.

But from the data gathered, I would say there isn't that much. It's either 1 or 0 and nothing in-between to look at or talk about, that is of course from looking at compressed Facebook clips and not the radiometric videos at 120fps that those cameras can do.

[Ultrapurple]

I know this is something of a zombie thread now but one of the things mentioned earlier was trying to image the moon with a thermal camera. I came across a fantastic piece of work by Flir on YouTube:

[Vipitis]

coming across this really old topic from myself. but I also found a relevant resource here: https://adsabs.harvard.edu/full/2006SASS...25..151K/0000151.000.html -> someone use a single pixel scanning mwir camera that is cooled by liquid nitrogen to claim an image of mars using a telescope. I hope the link isn't paywalled.

I still have this dream in the back of my head.