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The main advantage of a reflective telescope is lack of chromatic aberrations, because light never disperses. The other, related advantage is that you don't nee
by formerly_proven 3y ago
The main advantage of a reflective telescope is lack of chromatic aberrations, because light never disperses. The other, related advantage is that you don't need glass that's transparent over a large range of wavelengths. JWT ranges from the end of the visible spectrum to like 30 µm.
- delta_p_delta_x 3y agoCorrect. Almost all large telescopes (read: ~50 cm aperture and wider) are reflectors. Glass is used almost exclusively on camera lenses only, and that's because a 'reflector camera' would be un-ergonomic and impractical. Not much of a concern for a bunch of mirrors stationary in a building or rocketed up to space.
- dogsgobork 3y agoThere are some reflector lenses available for SLR cameras, not everyone likes their different optical properties though.
- dekhn 3y agoI have one of these- a 500mm "equivalent" (https://www.amazon.com/gp/product/B004WLEEHI https://www.amazon.com/gp/product/B004WLEEHI) and it's definitely got weird optical properties.
- namibj 3y agoSadly sensors are all bundled up with the rest of the camera, because a Schmidt camera (corrector plate like your objective, adjustable primary mirror, sensor directly in the primary focus with it's back facing the scene) can easily get a very wide aperture (e.g. nicely matching a CMV12000 with a fairly tame single glass up front and a tame mirror in the back, plus a slab and a plano-convex lens right at the sensor to flatten the field/focus, yielding 400mm f/2.0, though that's with the focal point dead center in the sightly over 800mm tube; still around f/2.4~f/2.8 brightness to the full f/2.0 sharpness (near center, but even at the corner you need a monochrome sensor to feel the mushiness)). Celeste's prosumer 8~14" (aperture) Schmidt-Cassagrain typically support replacing the secondary mirror with a camera mount to get that much shorter focal length (IIRC around f/5). Might be nice with one of those very narrow studio video camera bodies (e.g. Black magic has some); the catadioptric nature means you can carry even the very big ones on your shoulder (I'd highly recommend a gimbal if used for shooting from the shoulder).
- dekhn 3y agoI'd like to understand what you're saying better. I mainly purchased that "lens" because it was the most affordable way to upgrade to a higher magnification on a DSLR. But for another purpose (solar imaging), I'm actually moree interested in using machine vision cameras with C-mount. Aperture isn't super important because the sun has lots of photons (so many I have to use a filter that fits to the lens) but a flat field is dfinitely desired. I like the sensor you mentioned (CMV12000) but I assume it's obscenely expensive... $20K
- namibj 3y agoNo it's 2k$ last I checked.
- deleted 3y ago[deleted]
- gsliepen 3y agoA drawback is that you either have a spider construction blocking parts of its view (which in itself causes diffraction and reduces contrast), or you have an off-axis telescope, but this requires asymmetrical surfaces which are much harder to create than spherical and parabolic ones.
- zalo 3y agoFun Fact: Diffractive optics exhibit chromatic aberration in the opposite direction to Refractive optics, so the two can be used together to cancel each other out! Of course, that doesn’t help with the weight on a space-based telescope, but it was being considered quite frequently for VR Headsets a few years ago.