thermal astrophotography?

[Vipitis]

Hey,

I am new here. I recently had the idea to do astrophotography with my phones thermal camera. It is a CAT S60 with the Lepton in it.

I begun to take solar pictures, tried stacking and other processing. It was a hard task to get a pure thermal image out of the MSX capture with the stock MyFLIR app. In the end I used the desktop FLIR Tools software to get a unified temp color scale and pure thermal without any watermarks. I captured them with ShareX screenshots into png.

I did 33 photos on a tripod of the sun a few days ago. The first 4 images had a cold spot close to the sun, about the place where mercury was that day -but it can't be a planet that far away on my small sensor can it?

I will attach the final result.It was too large so I uploaded the images http://imgur.com/a/C9vXx

It won't get any better - maybe more frames and better processing.

what I want to ask: has anyone tried it as well? like shooting a few pictures from the sun or moon - at night or even at day?

where I need help with: telescope? is a thermal telescope even possible? for the Lepton in my CAT? Would it have any better results? How much does one cost? can I build one my own? with cheap optics somewhere or even household items?I do own a 3D printer which can help when constructing - but a thermally transparent lens with magnifying capabilities?

I will have a read through other posts now. Thanks George for letting my know about this place.

-Jan

[Kleinstein]

Usually IR images of the sky are difficult, because there is quite some absorption in the atmosphere. So one may see things like clouds of just areas of higher and lower humidity.

Pointing the camera directly at the sun can damage the sensor due to to much radiation. It depends on the lens though.

A DIY lens for thermal IR is very difficult, as there are not that many materials.
However a mirror will work in the IR range relatively well. The cheap solution would using a magnifying cosmetic mirror that uses a surface mirror (a few of them do). It should also be possible to apply a metal coating to a normal back side metalized one.

A somewhat crazy idea to test would be using suction / negative pressure to bring a membrane with metal coating (e.g. metalized mylar) in a concave form. I am not sure how good this will be.
The crazy non RoHS idea is to rotate a pot of mercury. Centrifugal force will form a near perfect parabola form for a focusing mirror. This is not a new idea - it has been done in the normal optical range.

A simple 3D printer is by far not good enough to make a near perfect optical finish.

[Kilrah]

The cheap solution would using a magnifying cosmetic mirror that uses a surface mirror (a few of them do). It should also be possible to apply a metal coating to a normal back side metalized one.

You shouldn't need that, glass is reflective to IR already.

[Vipitis]

The cheap solution

so a spoon could work as well? I don't think I got cosmetic mirrors around, but based on the reflectness of glass, a rounded glas, like a bowl could be worth a shot.

I would use the 3D printer to print housing and mechanics of a telescope or something, I won't be able to print any lenses or optics.

[Vipitis]

just buy good IR and first surface optics

but how well does normal IR optic like lenses work with thermal - are all IR transparent materials working for the thermal range of IR wavelenghts?

[Kleinstein]

For lenses there are different wavelength bands. The NIR part can use more or less normal glass like visible. The longer wavelengths use different materials, like germanium (expensive), LiF and others. They all have there limits and not all of them work well in the thermal IR band. However the thermal IR cameras usually use a similar band of something like 5-10 µm.

The advantage of mirrors is that they are usually wide band, usually visible to RF, maybe yellow to RF for gold. So a first surface mirror will work in the whole IR range, with very rare exceptions.

A spoon is rather small and usually they are rather distorted. The magnifying mirrors a relatively cheap at something like $10 and the surface is usually much better quality than what one would find in metal work or similar. Also the focal length might be about right and something like 10-20 cm is not a bad size. With image manipulation one can compensate for some distortion, but compensation for a blurry image adds noise and SNR is not that good on thermal cameras anyway.

[Bill W]

Moon image, with passing plane.



This was with a 46mm lens and 25um pitch sensor.

You need magnification and ideally reduced aperture so a very long focal length reflective system is the most likely to work on the sun or moon.  The lepton and lens will be analogous to the telescope eyepiece, so a Newtonian telescope design may work straight off.

Bill

[Ultrapurple]

I have done some test astrophotography using a Therm-App imager and a not-very-good 6" reflector telescope. My target was the moon - nothing else except the sun was bright enough, and I can easily line the telescope up on the moon with my other eye.

I was surprised to get images at all, so everything was better than I was expecting. I've attached a sample side-by-side of a visible (regular camera with zoom lens) and thermal image. The thermal image lacks a lot of detail but it is possible to see some features if you squint at it hard enough.

The original post on the Therm-App group has more details - see
https://www.flickr.com/photos/ultrapurple/21573112739/

I also used AutoStakkert! 2.1.05 to process a different stack of images for better contrast and resolution, see
https://www.flickr.com/photos/ultrapurple/21926397382/ for details

So the short answer is that you can get results with relatively simple equipment. My telescope optics are boggo standard, completely unaltered from visible light use. I might get better results with a wavelength-matched mirror but I was just playing around to see what I could achieve.

[Vipitis]

Hey,

I want to say a big thank for finding this old post and keeping me motivated.

Your sensor is far superior to mine but you made my decision on refractor versus reflector very clear.

I am still positive to get better results with the Lepton by using better capture if apps to lock a tempscale or do that in post.

I got some damage I my sensor while looking at the sun I believe so it will be mandatory to have bias and dark frames by using some kind of thermal reference for your stacking software for denoising and working against offsets.

If you are interested in astrophotography in general, or would love to talk about your success I this any more, please check the r/astrophotography subreddit and our Discord. I am very active in there as well and will be discussing your images now as a proof that is doable.

Thanks again for keeping me motivated on this topic and big kudos for those captures.

[sam1275]

I have done some test astrophotography using a Therm-App imager and a not-very-good 6" reflector telescope. My target was the moon - nothing else except the sun was bright enough, and I can easily line the telescope up on the moon with my other eye.

I was surprised to get images at all, so everything was better than I was expecting. I've attached a sample side-by-side of a visible (regular camera with zoom lens) and thermal image. The thermal image lacks a lot of detail but it is possible to see some features if you squint at it hard enough.

The original post on the Therm-App group has more details - see
https://www.flickr.com/photos/ultrapurple/21573112739/

I also used AutoStakkert! 2.1.05 to process a different stack of images for better contrast and resolution, see
https://www.flickr.com/photos/ultrapurple/21926397382/ for details

So the short answer is that you can get results with relatively simple equipment. My telescope optics are boggo standard, completely unaltered from visible light use. I might get better results with a wavelength-matched mirror but I was just playing around to see what I could achieve.

Err... Your telescope is transparent to both visual light and thermal? Or I missed something?

[Fraser]

Sam1275,

I believe a reflector telescope is being used here. As long as there are no glass lens elements in the optical path, it will work. A visible light refractor telescope would not work.

Surface coated mirrors are needed.

Fraser

[Vipitis]

He said it's a reflector telescope. Even the glass mirrors reflect a lot of the LWIR spectrum ad you may have noticed by pointing your camera on a window or a mirror.

Getting a better Mirror for the LWIR wavelength made out of Mylar or something to a telescope precision can be really expensive. And the results are truly impressive for a normal, visual telescope.

[Vipitis]

I found this paper on a similar topic a while ago;

I will just leave this in this thread for further reference and for the interested.


This might download a .pdf if the link works.
montana.edu/jshaw/documents/IR moon imaging smoke layers - Shaw et al - AO 2015.pdf

[Ultrapurple]

Yes, it's a simple reflective (Newtonian) telescope and all the mirrors are first surface. There is no glass in the way. As you'll see from the Flickr posts I simply mounted the imager in the place where the eyepiece would normally sit, in exactly the same way you do visible astrophotography with a DSLR or similar.

The field of view on my setup is just less than the moon's diameter. Rotating the imager in the eyepiece slot is a way to make the invisible area fall in an unilluminated bit of moon. You can see a photo of the setup here:
 https://www.flickr.com/photos/ultrapurple/16524885978/

I didn't manage to see any stars with my setup, although truth be told I didn't try too hard. The atmospheric attenuation plus the high f number of the telescope meant I was on a hiding to nothing anyway. Maybe if I'd had a cryogenic camera? Who knows. Maybe I'll try and find out one day!

I have used a germanium X3 telescope to try and look at the moon but the magnification wasn't high enough to be useful with my 19mm lens. I'm planning some further experiments down that route, one day, when I get a longer FL lens and some other goodies.

[Vipitis]

From what I saw in your Flikr(I spent the past 30 minutes browsing your whole history of Thermal Experiments) you did already a lot to get something.

Sun and moon is probably the easiest bodies to get. But sun is too dangerous to look at with a scope or a sensor at all.

When you look straight up on a clear night(heh) with various FoV... What kind of temperature do you get?

I asked FLIR via Twitter if it is possible to see meteors when they heat up the atmosphere but they said it would be really lucky to get something. Today Perseids peaked at a ZHR of 90 to 120 in some places and if I hadn't clouds I would be outside checking this out.

Can you potentially track the moon with your scope? You mentioned to have a GoTo - and use your many lenses to get even more magification at the cost of worse aperture overall?

It's a really interesting topic to me and what I have seen from your early, unprocessed side by side shot, there is some interesting things to discover.

Right now is the worst time to do moon photography as it's behind a lot of atmosphere. Being at a location with a moon closer to zenith would be giving far better results. (ideally leaving our atmosphere, but there seems to be no LWIR imagery available of the moon from satellites in LEO or even further.)

I can only recommend you to talk to some astrophotographers, they have a lot of knowledge and ideas even though nobody used LWIR wavelengths yet.

[Ultrapurple]

I'm afraid I can't remember what sort of temperature I was seeing on the display, and anyway I don't think the figure would be meaningful given the optical setup. When I point the camera straight up on a cloudless night using a normal lens I see reported temperatures like -20°C, but that's not really news.

You're right of course about it being dangerous to look at the sun with telescopes etc - that's why I said I could track the moon with my other eye!

Meteors have been tracked in broad daylight using thermal cameras for years. For instance, see Daylight Meteors, Brian Oughton, G4AEZ, RadCom March 2008 pp 64-65. Brian and friends used unspecified military thermal imagers that were probably made by Selex. There's a photo in the article that might let the eagle-eyed identify one or more of the cameras that was used. I've attached a relevant clip.

According to the last part of article,

"EQUIPMENT USED. The thermal imaging equipment used to capture the meteor images included both 3- 5µm and 8-12µm technologies. One idea was to determine which wavelength would perform the best in this task. As with many experiments with so many uncontrollable variables, there was no clear winner.
"What did come out as expected was that the latest generation equipment, using an 8-12µm (long wave) Cadmium Mercury Telluride detector with a resolution of 640 x 512 pixels, generally performed the best in terms of number of detections and clarity of image. Cameras of this kind are capable of exceptionally high sensitivity and resolution and are unfortunately likely to be outside the budget of the majority of amateur enthusiasts. It would be very interesting to try the same experiment with low technology equipment of the kind often available in the high street."

I like the idea that in 2008 one could buy thermal imagers (of any resolution or technology) on the high street.

I have never tried a similar experiment but I guess it is something I could try. The Perseids peaked last night with a good show but unfortunately I was tucked up in bed.

I'm sure I'm not the only person who has ever pointed a thermal camera at the moon. There are enough high end military imagers out there with good optics that would probably give quite a decent picture and there is always downtime when you're training or whatever so it's possible to have a play. But not many squaddies seem to post work photos of classified equipment online - something to do with getting court-martialled, I think!

[Fraser]

I should fire up my military long range thermal camera and see what it makes of the moon 

It is fitted with a catadioptric lens and capable of very long range observation. The moon is a bit further than it was designed for though 

Fraser

[Fraser]

Regarding the temperature that is displayed when pointing the thermal camera at the clear sky. I have done this many times.

The reading is, and always should be, the same on a standard thermal camera. The reading should be the minimum temperature capability of the camera plus an indicator that the temperature is out of range.

At 35000 ft the temperature is already well below the capability of most cameras at colder than -55C. Most thermal cameras 'bottom out' at -40C, or -20C for cheaper units. It should be understood that most budget thermal cameras become very inaccurate when measuring below 0C. Industrial thermal cameras receive additional calibration at manufacture to make them more accurate below 0C, but they still cannot measure below -40C.

Hope this helps answer the question. The reading should be -40C with 'out of range' alert active during such a test.

Fraser

[Ultrapurple]

The moon is a bit further than it was designed for though 

Fraser

I can lend you my tall tripod if will help...

I keep looking at the x10 LWIR telescopes that turn up from time to time on eBay but they are usually $1000+ and located in Australia so shipping and taxes would probably triple that.

[Fraser]

A word of warning on those thermal telescopes. They are often Inframetrics units and they come in two flavours..... SWIR-MWIR and LWIR. The shortwave and Medium wave IR types will not work with Long Wave microbolometer based cameras. I have contacted sellers on several occasions and it has not been clear which band they are designed for. If you buy the wrong type, it is an expensive paperweight.

In case anyone is wondering why a mirror type lens would be subject to band limitations....... they contain mirrors plus a collimator lens set at the output to the camera. It is the AR coated collimator lenses that limit the band in which the lens may be used. It is possible to find the dual band lenses that can operate at SW-MW and LW, but you need to check before buying.

I have both MW and LW IR cameras so in theory, if I can find one cheap enough, I could use one of these telescopes.

Fraser

[Ultrapurple]

Noted about the coatings - thanks.

I started musing whether an offset-fed solid satellite dish would be good enough to use at LWIR. Granted, the usual spec of 1/4-wave at (say) 15GHz (ie 5,000µm) would be way off what would be required for good performance at 10µm (ie better than 2.5µm surface accuracy) but as we all know, even cheap concave shaving mirrors can (just about) produce usable images in the visible range, albeit a little fuzzy.

So, I wonder: next time I see a large-ish solid offset dish going cheap, is it worth spraying on something that'll reflect at LWIR and seeing if I can get images out of it if I put a staring array at the focal point?

Answers on a postcard, please.

[sam1275]

Thank you everyone for explain.

[Vipitis]

Coating an off-axis dish:

try mylar foil. or experiment with something like chrome as a spray.

for your stated article on finding meteors with military grade thermal cameras, can you share a link or something? I was unable to find anything with my google searches on the topic or names you listed.

 I am really glad this thread is up again and we spark some interest in more people.

[Bill W]

Regarding the temperature that is displayed when pointing the thermal camera at the clear sky. I have done this many times.

The reading is, and always should be, the same on a standard thermal camera. The reading should be the minimum temperature capability of the camera plus an indicator that the temperature is out of range.

At 35000 ft the temperature is already well below the capability of most cameras at colder than -55C. Most thermal cameras 'bottom out' at -40C, or -20C for cheaper units. It should be understood that most budget thermal cameras become very inaccurate when measuring below 0C. Industrial thermal cameras receive additional calibration at manufacture to make them more accurate below 0C, but they still cannot measure below -40C.

Hope this helps answer the question. The reading should be -40C with 'out of range' alert active during such a test.

Fraser

To get to 35,000 feet you have had to go through a fair bit of not-all-that transparent atmosphere that is a fair bit warmer - so you will not get -70°C but an average* of the air column.  Likely to be dominated by the first few thousand feet of warmish dampish air, so -15°C is probably about right unless somewhere very dry or working only in the higher transparency wavelengths.

On a common 7-14 system it is quite possible to lose 10% contrast over 4m on a steamy summer day.

* that is a Planck compensated average in the 7-14µ band of course.

Bill

[Ultrapurple]

for your stated article on finding meteors with military grade thermal cameras, can you share a link or something? I was unable to find anything with my google searches on the topic or names you listed.

Unfortunately as far as I know there is no public domain version of the article although it might turn up on Scribd or something.

A summary of the article is as follows.

Brian Oughton's job involved working with sensitive infrared detectors (I think for Selex). During some camera testing some colleagues captured by chance what they thought might have been a daylight meteor. So they decided to make a determined effort to see meteors in daylight during the 2007 Perseids.

As their cameras had a relatively narrow field of view they used ham radio equipment to search for radio 'pings' that would not only give them a direction to point to but also confirm the presence of meteors.

Between 6 and 8am on 13 August 2007 the group had captured numerous meteor trails on video using the various IR cameras and later analysis showed that whilst most were Perseids, some may have been random meteors from other directions. There was good correlation between the radio records and IR video, giving a high degree of confidence that they had indeed been seeing meteors on the IR cameras.

The article included a photo of the team standing in front of some sort of light military vehicle that appeared to have a (possibly thermal) camera on a mast, and a member of the team holding a thermal camera (see image crop above). There were also four stills taken from the video recording of a meteor crossing the field of view: frankly, it was just a small indeterminate white blob with no distinguishing features.

The conclusion was the "Equipment Used" section, which I reproduced in full above, and that is the only section that really contains any technical information.

Hope this helps