Author Topic: Making Seek Thermal camera compatible with reflector telescope.  (Read 442 times)

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Offline Tamiore

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Making Seek Thermal camera compatible with reflector telescope.
« on: October 04, 2020, 11:31:24 am »
Hi everyone,

Long story short: I want to try and see if it would be possible to use a thermal camera (seek thermal pro, to be exact) with a reflector telescope. (In principal, since reflector telescopes only use mirrors, and metal mirrors reflect in thermal IR just fine, I don't see why this shouldn't work, but maybe I'm missing something.)

As of right now, I have the camera itself at my disposal, but I don't have any exact model of the telescope, yet.

Initially, the plan was something like "just go to store that has telescopes in the showroom (I have several such stores in my city) and see which telescope works best with my camera".
However, I run into one rather obvious problem: all telescopes use an eyepiece to focus image onto the smartphone camera (which is an equivalent of seek thermal as far as focusing goes). And eyepieces use glass lens, so IR doesn't get though. Now, practically all telescope do have an option of projecting the image directly onto the camera's matrix (without an eyepiece, that is). But that requires me to remove objective from camera. Which brings us to this topic.
Can someone (who has a bit more experience disassembling seek thermal's) share their opinion on the following:

1) Is there any major reason why removing focusing lens from it (temporarily) is a bad idea?
2) Is it even possible to remove focusing lens while keeping the rest of the housing in place (to avoid getting stray light from all angles).
3) Any other thoughts why this is a dumb/implausible idea?
« Last Edit: October 04, 2020, 11:33:26 am by Tamiore »
 

Online Vipitis

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Re: Making Seek Thermal camera compatible with reflector telescope.
« Reply #1 on: October 04, 2020, 11:42:33 am »
I am sure Ultrapurple will reply in a their  success of getting a photo of the moon.

Projecting through an eyepiece into a lens will always be losses, but any proper telescope will slow you to remove the eyepiece and mount a camera in prime focus. As the standard is usually T2, you can even buy focussing adapters to common camera mounts. Your best bet is to unscrew the lens and just hold it in place with some tape or cardboard. Getting it in plane will be difficult. (You might be able to find an adapter for the thread, or print one... But you will need to know exactly what to look for).

Having the sensor exposed does require some care, so don't expose it to dust and avoid direct sunlight.

One issue you will run into is that most reflector telescope (Newtonian design), will be rather slow, giving you f/4.5 or f/3.1 at best (faster scopes are available but expensive. Also under that the mirrors are meant for visual so they don't reflect 100% in LWIR. You can get your mirrors coated with goal(or mylar) to get really high reflectivity and better performance. I can find you a few papers on ground observations using an OTS microbolometer later.
 

Online Fraser

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Re: Making Seek Thermal camera compatible with reflector telescope.
« Reply #2 on: October 04, 2020, 12:01:36 pm »
Vipitis has provided a comprehensive answer but a couple of comments from me.

I would not operate a Seek Thermal camera without a lens fitted. Dust on the microbolometer is a serious risk and cleaning the microbolometer without damage to the exposed bond wires is the challenge you face if dirt does get on the microbolometer window. The FFC shutter flag also gets in the way when trying to clean the microbolometer.
If you must operate without a lens, I recommend the use of a an AR coated Germanium window to protect the camera from dust etc.

First surface mirrors used in optical telescopes mat actually have a visible light transparent layer on them to protect the mirrors from moisture. The mirrors may not be very efficient as a result. Do not expect better than 50% reflection from each mirror as a result.

Consider what you are trying to image and consider how many pixels will be illuminated by the target using a particular FOV telescope. QVGA is very low resolution for astronomy unless the target is large in the FOV. If the target will only illuminate 1 pixel, you are wasting your time and effort building the telescope system. As the camera may well not even display the target. Also consider what will be in the FOV....... very cold atmosphere and space...... this can understandably really upset some thermal cameras auto ranging and you will need to operate the camera in full manual ranging mode. Temperature measurements of targets will very likely be meaningless unless some serious maths is applied to them to account for the effects of the earths atmosphere.

Finally...... Noise, Noise, Noise ! Most Microbolometer based thermal cameras are forever fighting the noise that the sensor technology produces. The camera OEM’s use various noise reduction approaches and some have to be quite harsh in their characteristics. This is why a single pixel target can easily be lost in the video processing as it may be identified as just noise. The Seek Thermal series of cores, including the Pro series are amongst the most noisy cores on the market. They are excellent miniaturised cores but they use tiny 12um insensitive pixels and require masses of noise reduction to produce a clean image. This is why I would not use a Seek Thermal cored camera as the basis of thermal astronomy. They are just too noisy for the task. What is truly needed is a high performance cooled thermal camera that is very low noise and very sensitive. My FLIR SC was designed for use on Telescopes and is both low noise and sensitive. It is also high speed as it was designed for missile range imaging of missive tail plumes ! The original price of $150K is a bit scary though.

Fraser
« Last Edit: October 04, 2020, 12:29:30 pm by Fraser »
Cogito, ergo sum
 

Offline Bill W

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Re: Making Seek Thermal camera compatible with reflector telescope.
« Reply #3 on: October 04, 2020, 12:06:02 pm »
The main issue is getting to the prime focus plane.  As you have to have a pure reflector (ie not Schmitt etc) this plane can be inside the scope on cheaper designs not intended for SLR/CCD imaging.

You might need / want to consider putting the Seek on axis rather than using the secondary mirror.

Bill

Online Fraser

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Re: Making Seek Thermal camera compatible with reflector telescope.
« Reply #4 on: October 04, 2020, 12:23:48 pm »
What the professionals use...... they seem to favour the twin mirror Axial type of telescope That projects the image out of the rear and onto the camera system. In the attached images you will see the FLIR SC series camera, like mine, attached to the rear bulkhead of the telescope. As Bill has suggested, it might be a viable option to place the camera where the second mirror would sit but I am uncertain of the negative effects of the cameras self heating on the system.

Fraser
« Last Edit: October 04, 2020, 12:30:38 pm by Fraser »
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Online Fraser

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Re: Making Seek Thermal camera compatible with reflector telescope.
« Reply #5 on: October 04, 2020, 12:42:47 pm »
This might sound crazy, but I think you may be best served if yo buy a really cheap reflector telescope, either new or used. The $150 sort of thing. Why ? Well I bought such a telescope from a charity shop fir £20 and I note that it uses polished aluminium mirrors (cheap to produce) and, if the slight corrosion spotting is a sign, they mirrors are uncoated !

Fir information, AGEMA Scanner type thermal. Cameras also used polished Aluminium mirrors in the scanning assembly. No gold plating or first surface glass mirrors in the well respected Thermovision 4xx and 8xx series cameras.

Thecatrached image is of a £169 Newtonian telescope but I am using it as just an example. You need to do your own investigation to find a suitable model. Look in the second hand sources as well. These are often cheap on eBay or in charity shops.
Fraser
« Last Edit: October 04, 2020, 12:45:26 pm by Fraser »
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Offline Tamiore

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Re: Making Seek Thermal camera compatible with reflector telescope.
« Reply #6 on: October 04, 2020, 01:09:37 pm »
Thanks for all the information.
To be honest, at this point I'm more focused on the camera side of things. (As in, how to modify it to remove "native" objective without damaging it or exposing it to further harm.

I guess the primary suggestion here would be to get an AR germanium window and replace the native objective with it?
 

Offline IwuzBornanerd

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Re: Making Seek Thermal camera compatible with reflector telescope.
« Reply #7 on: October 04, 2020, 05:24:20 pm »
@mahony has done this with a TE-V1 & posted photos of the moon in reply #302 on the original imaging gallery:

https://www.eevblog.com/forum/thermal-imaging/thermal-imaging-gallery/msg2205606/#msg2205606

As for removing the seek lens, I suggest looking at the Seek lens repair thread:

https://www.eevblog.com/forum/thermal-imaging/seek-thermal-lens-repair/

I believe the Pro lens configuration is the same as that of the XR, but I have not cracked open a Pro to prove it.

One of the things on my "wish list" is to take an ordinary magnifying "make-up" mirror & try this concept by mounting the camera with lens off directly on axis over the mirror.  The 3X mirror gives about a half meter focal length I think.  The moon will be quite a big part of the frame at that point.  I expect the focal plane to be different than for visible light with this mirror but with a polished aluminum mirror I expect it would be the same, so one could find it with a webcam; but that might not help much since it is such an exacting measurement to duplicate to another device. 

There are some "solar furnace" things available with aluminum mirrors which I also have considered using...When I find the time & "gumption".
I am not opposed to exercise, unless it is an exercise in futility.
 

Online Vipitis

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Re: Making Seek Thermal camera compatible with reflector telescope.
« Reply #8 on: October 04, 2020, 06:45:03 pm »
I'd like to link to me very first post on this forum, when first exposed here without much knowledge: https://www.eevblog.com/forum/thermal-imaging/thermal-astrophotography/msg1195461/#msg1195461 this was about the idea of ground based astronomy using thermal cameras. But it went into all kinds of interesting discussions. It feels odd to see how primitive I was thinking back then. The cosmetic mirror doesn't really work, as you barely get anything in focus that is further away and there is awful aberrations, but I suggest you to still give it a try. There are mirror telescope (schmidt design - the donut primary) and some form members have those. On my desk right now I have a 150mm f/1 refractive Ge lens that has some internal debris and a lose first group for focusing(it got an image circle of 20mm and more).

here are two papers that I have found, on actual astronomy using microbolometers while on the ground: https://arxiv.org/pdf/1912.08276.pdf and https://www.researchgate.net/profile/Joseph_Shaw2/publication/269726004_Infrared_Moon_imaging_for_remote_sensing_of_atmospheric_smoke_layers/links/54b001160cf28ebe92de3c0d/Infrared-Moon-imaging-for-remote-sensing-of-atmospheric-smoke-layers.pdf

As OP never said their intend, we all just assumed it is astronomy, here is handy tool to calculate the fov on a moon shot for example.
given 12µm pixels and QVGA resolution, a 300mm focal length will give you the attached fov.
 

Offline IwuzBornanerd

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Re: Making Seek Thermal camera compatible with reflector telescope.
« Reply #9 on: October 04, 2020, 11:05:03 pm »
The cosmetic mirror doesn't really work, as you barely get anything in focus that is further away and there is awful aberrations, but I suggest you to still give it a try.

Hmmm...So the mirror is not such a nice perfectly spherical surface?  I figured it was worth a shot since the manufacturing process is so common & old that it was easy to make it good.  I also figured that small imperfections would be less noticeable in thermal than in visible light, and on large objects vs. tiny ones.  The tight aperture & "weak" reflection from glass make it only useful for rather warm objects.

As you suggest, I may still try it as an interesting experiment, but it is a very low priority task.  Once I get that far I might also try it on the sun viewed through the "energy efficient" IR reflective windows in my house.
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Offline Bill W

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Re: Making Seek Thermal camera compatible with reflector telescope.
« Reply #10 on: October 05, 2020, 10:29:55 am »

Hmmm...So the mirror is not such a nice perfectly spherical surface? 

I suspect that is the problem, spherical aberrations.  You really need a parabaloid.
All those nice 'small angle' approximations from school are not always good enough in the real world.

Bill


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