3182: Telescope Types
| Telescope Types |
 Title text: I'm trying to buy a gravitational lens for my camera, but I can't tell if the manufacturers are listing comoving focal length or proper focal length. |
Explanation
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This is one of 57 incomplete explanations: This page was created recently ACCORDING TO A TELESCOPE POINTING BACK IN TIME. Don't remove this notice too soon. If you can fix this issue, edit the page! |
This comic shows diagrams of a number of different types of telescope, some real and others made up by Randall. It includes both refracting and reflecting designs; see 1791: Telescopes: Refractor vs Reflector for the important (according to Randall) differences between them.
| Type | Real? | Refractor/Reflector | Description |
|---|---|---|---|
| Prime Focus | Yes | Reflector | A telescope design where the observer/receiver is situated at the focal point of a single mirror. Rare in optics, but a common design in radio telescopes. |
| Herschelian | Yes | Reflector | A telescope design much akin to Prime Focus but with the mirror tilted so that the observer does not block incoming light. Named after astronomer William Herschel. |
| Newtonian | Yes | Reflector | Newtonian telescopes employ a second, flat mirror along with the primary parabolic mirror. |
| Galilean | Yes | Refractor | What might usually come to mind when picturing a telescope. A long tube that uses lenses rather than mirrors (making it a refracting telescope) to magnify images. |
| Keplerian | Yes | Refractor | An improvement on Galilean telescopes, using a convex lens rather than a concave one at the eyepiece (as shown in the diagram). It does however invert images. |
| Gregorian | Yes | Reflector | |
| Cassegrain | Yes | Reflector | |
| Cardboard tube | Yes, but not as a telescope | Neither | Looking through a tube helps you focus by removing distractions, but doesn't magnify the object being viewed. |
| Kaleido | Yes | Reflector? | A kaleidoscope isn't really a telescope, because the non-viewing end is closed. You view many reflections of tiny objects at the end, rather than remote objects. The mirrors are also usually flat, so there's no magnification. |
| Liquid Mirror | Yes | Reflector | A telescope using a rotating pool of reflective liquid (most commonly mercury) as a mirror. The diagram adds a straw so that someone can drink the liquid. This would likely not end well for the drinker. |
| Narcissian | No | Reflector | This is like a prime focus telescope, but the focus is outside the end of the telescope where the viewer is located. So they can only see themselves, greatly magnified. This is inspired by the myth of Narcissus, who fell in love with his reflection in a pool of water. |
| Gravitational | Yes | Refractor | These can't be constructed on Earth[citation needed], they're formed naturally by large stars (particularly black holes) and galaxies. There are proposals to launch missions to the very far reaches of the Solar System to "construct" a Solar gravitational lens telescope, but the masses and distances involved are not compatible with consumer camera hardware. In the title text, Randall makes a pun on whether the listed focal length of a gravitational lens is measured in the comoving or proper reference frame, i.e. whether the expansion of the universe (between the place and time of the lens's creation or construction and Randall's decision to purchase) has been factored out or not. At the cosmological scales between stars and galaxies, where gravitational lensing is most relevant, this is a useful distinction to make, but stars are not for sale (by any legitimate commercial entity) and so nobody would be advertising any focal length in either reference frame for any purchaser. |
| Geological | No | Reflector |
Transcript
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no vampire jokes π₯ (1791) TheTrainsKid (talk) 00:08, 18 December 2025 (UTC)
Got down some preliminary descriptions of each telescope type used 185.132.133.218 01:44, 18 December 2025 (UTC)
insert that one mickey mouse meme with the caption "what a fucking narcissist" Yaokuan ITB (talk) 02:33, 18 December 2025 (UTC)
abnormally low joke-to-real ratio for this format of comic! 2601:241:8002:3E0:C0A2:9DA:ED39:D13F 03:21, 18 December 2025 (UTC)
- I noticed that... I think this might've originally been 'look at all these cool telescope types', but then he realized he had to put some sort of joke somewhere. --DollarStoreBa'alConverse 03:27, 18 December 2025 (UTC)
Can someone make a category for The Core (2003)? It's been mentioned often enough. 83.245.251.49 09:22, 18 December 2025 (UTC)
> This would not [β¦] end well for the drinker.
Would it though? Drinking elemental mercury, while not great on nutritional value, should be mostly safe (and I'm using that word quite loosely). The most danger would be while drinking and expelling it, when there's a danger of inhaling mercury vapors, right? --Coconut Galaxy (talk) 10:29, 18 December 2025 (UTC) Add comment
