With a 76cm Auxiliary telescope at the McMath/Pierce, we found that flares are seen in the continuum images at 5 and 8 microns, and that the contrast was better at 8 than at 5. Ultimately, my motivation is some of the work we did a few years ago at Kitt Peak. This puts an image scale at about 1700 arcsec per pixel, which fits with the roughly 1 pixel diameter images of the Sun and the Moon that I took. With an array size about the same width, that's an f/1 lens. The pixel size is listed at 12 microns (here: ) and with the nominal FOV listed it looks like the integrated lens is about 1.9mm focal length. Yes, it does seem like the detector isn't cooled. I am under the strong impression that SEEK and FLIR commercial user camera (and add-on to smartphones) are not cooled. Very interested to see how is it going to turn out. I'm getting the suspicion that Tucson in the summer isn't an ideal time to start up some night-time IR thermal imaging.Įdited by MattPenn, 02 June 2020 - 11:12 PM. Tonight's run outside was very successful at finding clouds, bugs and bats. If you don't mind I'll ping you with some questions later. It won't be a 4m off-axis reflector, but it'll be something to keep my hobby interest going! After that it might be interesting to look at getting a cheap lens to act as an eyepiece to collimate and magnify like you discuss above. Hoping that the moon will be bright enough to compensate. that will produce a lot of background for sure. My first attempt will likely be using an f/8 6" Newtonian at prime focus. I'm not sure what the cooling is, but it runs off a USB line so it can't be anything fancy. So now that I'm an amateur, I don't have that kind of budget anymore. and unofficially capturing some data at 20 microns before I resigned and turned into an engineer. I see you've done optics before! I worked in solar physics, publishing papers with data from 1 to about 4.6 microns (that camera used a 1k x 1k InSb array at 35K). Germanium refractive index is slightly over 4, thus it reflects about 36% at each surface!Īnyway, this is how your lens can be augmented.ĥ0mm 8X LWIR afocal.len 570bytes 48 downloadsĮxcellent, thanks Mike. And germanium MUST be anti-reflection coated. But IR lenses are not cheap, and unless you know someone that can custom-make germanium lenses for you, it's not going to be cost attractive. If you measure your horizontal and vertical field of view, it's easy to design an afocal to increase the collecting aperture and narrow the FOV. But that doesn't take away from your camera's ability to image in the infrared. Your camera is most likely uncooled, making it much less expensive, but at the cost of minimum resolvable temperature differences. For uncooled IR cameras, though, it might be the lens aperture stop at ambient temperature, termed the "warm stop". Where is the actual aperture stop then? For cooled LWIR cameras it is the cold stop, an aperture located inside the 77ºK temperature region containing the focal plane. All infrared lenses must have larger clear apertures than the beam passing through them to keep hot edges from intruding into the path and showing up in the image. Vignetting in infrared systems is particularly bad, as anything not made from infrared-transmitting material will appear hot, spoiling image contrast with stray out-of-focus "light" (thermal emissions). The real exit pupil of the afocal assures that collimated infrared radiation emitted from the afocal can be made coincident with the entrance pupil of your lens, thus there will be zero vignetting. A 2º field of view at the front of the afocal gets magnified to a 16º FOV at the exit pupil. Like any of our telescopes, the ratio of the afocal entrance pupil diameter to the exit pupil is the magnification, which in this example is 8X. The first lens focuses long-wave infrared (LWIR), and a second smaller lens re-collimates the light, which passes through a real external exit pupil (i.e., it acts exactly as an eyepiece). The clear aperture of the afocal can be several times larger than your camera lens aperture. It can thus be fed from an afocal system like I show here that emits collimated light with some magnification.
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