Ultrapurple
The Moon, 500mm optics, thermal image
Having first established that it was possible to detect the Moon using the Therm-App thermal camera, I set about gathering the necessary paraphernalia to get a close-up shot. A focal length of 500mm felt about right, so that's what I used. It also helped that it's what I had lying around.
I will be the first to admit that, in some respects, this is another deeply unimpressive image. It's not very sharp and there is virtually no surface detail. On the other hand, it is quite impressive to be able to focus on the Moon at frame-filling size with a thermal imager in your back yard. It took me quite a while to achieve that for the first time at visible wavelengths with a 35mm camera.
Next on the agenda will be trying to get some surface detail. I suspect the lack of detail in this image is simply down to the fact that the Moon is of fairly even temperature where it is evenly heated by the Sun. You only have to look at the difference between a full Moon photo and a waxing or waning Moon photo to see the beneficial effect of low-angle lighting on the visibility of craters, and I expect the same applies in thermal terms. But I had a clear sky tonight and just enough time to set up, so I tried it and it worked. Finessing the results can come later.
The image is relatively low contrast and I am surprised just how cold the Moon registered: it came up as 42°C and very bright when using the 19mm germanium lens and I would have expected it to be overwhelmingly bright with the 500mm optics. However, I have no measure of the efficiency of the longer focal length apparatus other than a dim memory of it having a very small aperture, somewhere in the region of f/11. Given that most optics used with uncooled microbolometers tend to be in the region of f/1 to f/1.4 I think it's amazing I saw anything at all, even from a (very) bright target. I believe we're looking at about a factor of 50 less energy reaching the sensor than it would get from a f/1 lens - and that is optimistically assuming equal efficiency.
Comments are warmly invited. If you like this image, please join the Therm-App (and others) thermal imaging group at www.flickr.com/groups/therm-app-users/
The Moon, 500mm optics, thermal image
Having first established that it was possible to detect the Moon using the Therm-App thermal camera, I set about gathering the necessary paraphernalia to get a close-up shot. A focal length of 500mm felt about right, so that's what I used. It also helped that it's what I had lying around.
I will be the first to admit that, in some respects, this is another deeply unimpressive image. It's not very sharp and there is virtually no surface detail. On the other hand, it is quite impressive to be able to focus on the Moon at frame-filling size with a thermal imager in your back yard. It took me quite a while to achieve that for the first time at visible wavelengths with a 35mm camera.
Next on the agenda will be trying to get some surface detail. I suspect the lack of detail in this image is simply down to the fact that the Moon is of fairly even temperature where it is evenly heated by the Sun. You only have to look at the difference between a full Moon photo and a waxing or waning Moon photo to see the beneficial effect of low-angle lighting on the visibility of craters, and I expect the same applies in thermal terms. But I had a clear sky tonight and just enough time to set up, so I tried it and it worked. Finessing the results can come later.
The image is relatively low contrast and I am surprised just how cold the Moon registered: it came up as 42°C and very bright when using the 19mm germanium lens and I would have expected it to be overwhelmingly bright with the 500mm optics. However, I have no measure of the efficiency of the longer focal length apparatus other than a dim memory of it having a very small aperture, somewhere in the region of f/11. Given that most optics used with uncooled microbolometers tend to be in the region of f/1 to f/1.4 I think it's amazing I saw anything at all, even from a (very) bright target. I believe we're looking at about a factor of 50 less energy reaching the sensor than it would get from a f/1 lens - and that is optimistically assuming equal efficiency.
Comments are warmly invited. If you like this image, please join the Therm-App (and others) thermal imaging group at www.flickr.com/groups/therm-app-users/