--- Log opened Fri Dec 10 00:00:56 2021
01:25 < maaku> how do people have time to read a 50-page blog post by gwern or scott alexander?
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03:28 < fenn> https://hackaday.com/2021/12/09/molding-complex-optics-in-a-completely-fluid-system/
03:29 < fenn> .title https://www.osapublishing.org/optica/fulltext.cfm?uri=optica-8-11-1501&id=464960
03:29 < saxo> Fabrication of freeform optical components by fluidic shaping
03:29 < fenn> i think you could get more degrees of freedom with applied electric fields to control the wetting angle between the two fluids
03:35 < fenn> these captchas are getting out of hand
03:37 < fenn> as a human, what would you expect to type when presented with this? http://fennetic.net/irc/captcha_optica_wtf.png
03:37 < fenn> if you guessed "OEciA" you would be so, so wrong
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05:03 < muurkha> maaku: start at the beginning, read until you reach the end, then stop
05:06 < muurkha> fenn: good point
05:09 < fenn> i guess you're saying "don't read the comments"
05:09 < muurkha> it's optional
05:09 < fenn> which reduces it from 50 pages to 5 pages
05:10 < fenn> .title http://youtu.be/mfAGivG9Koc
05:10 < saxo> Making DIY Lenses with Epoxy - YouTube
05:10 < fenn> lots of very specific information if you actually decide to do this
05:11 < fenn> he needs to add "grog" to his molds
05:21 < fenn> .wik CR-39
05:21 < saxo> "CR-39, or allyl diglycol carbonate (ADC), is a plastic monomer commonly used in the manufacture of eyeglass lenses alongside the other material PMMA (polymethyl methacrylate). /  The abbreviation stands for 'Columbia Resin #39', which was the 39th formula of a thermosetting [...]" - https://en.wikipedia.org/wiki/CR-39
05:50 < fenn> i wonder why nobody ever does two-part molds, with an inner mold surface of silicone, and an outer rigid backer of, say, plaster
05:51 < fenn> the plaster part has a simpler, non-undercut surface so it's easy to remove from the silicone, and then the silicon peels off the finished part
05:51 < fenn> uses way less silicon so it's not as expensive
05:51 < fenn> silicone*
05:52 < fenn> since the plaster is very rigid it should result in a more accurate surface than a completely flexible mold
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08:25 < superkuh> CR-39 is by far the best material for eyeglasses, imo. Decent refractive index but more importantly it has a fairly high abbe number.
08:28 < kanzure> https://news.ycombinator.com/item?id=29510672
08:28 < L29Ah> tfw Zenni doesn't tell the names of the available materials except polycarbonate that sucks
08:28 < fenn> .t
08:28 < saxo> HN has really embraced our current techno-pessimistic culture, so all the things... | Hacker News
08:29 < fenn> a comment on "Ask HN: Where do you find weird and wonderful future tech nowadays?"
08:29 < superkuh> zenni lenses are okay if you have moderate eyesight. But anything beyond 8 diopter or so and it's not worth trying them.
08:29 < L29Ah> oh, and CR-39 that sucks too but not as much
08:29 < superkuh> Better to go local and get custom spherical curveture and bevels.
08:29 < L29Ah> i went local and was shocked by prices and unavailability of titanium frames with huge lenses
08:32 < L29Ah> grabbed https://www.zennioptical.com/p/mens-halfrim-memory-titanium-aviator-eyeglass-frames/1714?skuId=171412 in the end
08:33 < muurkha> does "memory titanium" mean Nitinol?
08:33 < L29Ah> idk but it is springy as hell
08:33 < superkuh> People with minor vision corrections don't have to worry about chromatic abberation, but it's really the limit on effective glasses for higher prescriptions material-wise.
08:33 < L29Ah> took a lot of effort and some tools to get it bent around my face
08:34 < fenn> superkuh: would it be possible in principle to use mirror optics?
08:34 < superkuh> I can't imagine how.
08:34 < muurkha> three reflectors over each eye
08:34  * darsie has -4 D or so.
08:34 < superkuh> http://eyestilts.com/log04.html
08:34 < superkuh> Tangential.
08:35 < L29Ah> the frame just doesn't care if you fold the lenses together as far as possible, for instance
08:35 < fenn> a convex mirror ring and a secondary mirror over the eye. the secondary could be half-silvered so others can see your eyes
08:35 < muurkha> one that reflects the beam four centimeters to the left, one that reflects it back over the eye, and a third one that redirects it toward the world again
08:38 < fenn> my idea was basically this but with a demagnifying mirror (a convex mirror) instead of a concave mirror https://en.wikipedia.org/wiki/Cassegrain_telescope
08:38 < fenn> anyway i suck at optics
08:40 < Malvolio> (see also ##optics for more optics)
08:57 < L29Ah> https://www.cyclingweekly.com/products/are-ford-about-to-reinvent-the-bicycle-derailleur nitinol as electromechanical drive, cute
08:57 < L29Ah> apparently no commercial product yet tho
08:58 < muurkha> why is nitinol so expensive?  I mean it's orders of magnitude worse than its component metals
08:59 < muurkha> just because vacuum?
08:59 < L29Ah> because it's a royal PITA to do anything with it
09:00 < L29Ah> or maybe just underdeveloped market? shouldn't differ much from titanium tbh
09:01 < muurkha> it's very different from titanium.  I mean I think it has about as much in common with titanium as beryllium copper has with copper
09:31 < Malvolio> gee. how do you sit through a 5 hour podcast? some rather lengthy content is clearly meant for cab drivers and pilots and people who wear comfortable shoes
09:40 < Malvolio> and the types of people who host and attend lectures and podcasts. :x bbl
09:43 < muurkha> .t https://birdsite.xanny.family/mattparlmer/status/1465807303895048192#m
09:43 < saxo> URLError: <urlopen error [SSL: SSLV3_ALERT_HANDSHAKE_FAILURE] sslv3 alert handshake failure (_ssl.c:720)> (title:73)
09:43 < muurkha> .tw 1465807303895048192
09:43 < saxo> Banksian modafinil rationalists vs Buddhist LSD rationalists // Many such cases (@mattparlmer)
09:44 < muurkha> .tw 1465809376942383108
09:44 < saxo> The chad "let's build rockets, reactors, and expert systems so we can get this interstellar colonization project going" vs the virgin "we're not a sex cult, we just hang out in grouphouses in Marin while we wait for not-God to initiate the not-rapture" (@mattparlmer, in reply to tw:1465807556580986885)
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14:50 < docl> https://alanse.medium.com/why-is-everyone-so-consistently-wrong-about-launch-assist-systems-d21288084421
14:51 < docl> .title
14:51 < saxo> Why is Everyone so Consistently Wrong about Launch Assist Systems? | by Alan | Medium
14:51 < docl> alan is against tethers, wish he'd gotten a little more into why
15:01 < docl> (for mx transfer purposes, specifically)
15:01 < fenn> before when i said the orbital ring would constantly be cycling tension, i meant in a system where the mass bolts are thrown around by tethers at each station on the ring
15:03 < docl> hmm. what's the min length of a tether that throws and catches stuff at orbital velocity wrt the station?
15:03 < fenn> who is az5_button?
15:03 < docl> that's roko
15:04 < docl> (the roko)
15:04 < fenn> there's no min or max length but the parameters change, (taper ratio, rpm)
15:05 < docl> doesn't it get to more absurd tensile requirements as you get shorter?
15:06 < fenn> i don't remember
15:06 < fenn> the timing issues get worse
15:07 < docl> gonna plug some values in here and see what happens https://www.omnicalculator.com/physics/centrifugal-force
15:07 < fenn> a=v^2/r
15:08 < docl> ok so if you have a tenth the length of r, a will be 10x as great
15:09 < fenn> no because v changes
15:09 < fenn> holding v constant, yes
15:10 < fenn> i was thinking rpm would stay the same
15:11 < fenn> a = (rpm * 2pi*r)^2 / r
15:11 < fenn> for funny a units with minutes in them
15:11 < docl> if you're talking about a system with the same orbit, v is constant... you can go to lower v by going further out of course, but it's going to be roughly 8km/s if you're trying to build the system in LEO
15:12 < fenn> what do you mean "the station"?
15:13 < docl> the stationary platforms you want your elevator cable attached to
15:13 < fenn> they should be exchanging masses at far greater than orbital velocity
15:14 < fenn> or it could be enormous masses at slightly greater than orbital velocity, but i've never seen anyone proposing that
15:15 < fenn> anyway let's say 30 km/s
15:18 < docl> for a 100m radius spinning tether with tip moving at 30km/s there's 900k gees
15:19 < fenn> here's an example calculation https://space.stackexchange.com/questions/40748/
15:19 < fenn> .title
15:19 < saxo> atmosphere - What would be the challenges for a 50 km long tether to the surface of Venus to get recurrent surface samples there? - Space Exploration Stack Exchange
15:21 < fenn> uh maybe a bad example, it's not immediately obvious how to plug acceleration into the equation there
15:23 < fenn> it's past my bedtime and i may be completely useless for the rest of eternity due to external factors
15:23 < fenn> read some of the papers in the wayback machine at tethers.com/...Bibliography.html
15:24 < fenn> there's definitely a taper ratio calculation in there somewhere
15:24 < fenn> gee forces don't really matter for throwing around dumb masses
15:25 < fenn> i agree that's an excessive number of gees, but all the numbers in that equation are silly
15:25 < docl> ok say we have a sling style tether launcher that's 50km long, and they can handle the 1800 gees with tapering, you could throw stuff from tether A to tether B at 30km/s that way with both being at the top of a space elevator, and space these in a polygonal shape around earth with good line of sight... it seems like a really awkward way to do an orbital ring to me but not fundamentally impossible
15:27 < fenn> there's also this "two stage tether" concept which i don't really get
15:27 < fenn> it's a spinning tether with a spinning tether on the end
15:28 < fenn> "two tier tether"
15:28 < fenn> and you can keep going with three tiers and so on
15:28 < fenn> it sounds horribly complicated
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23:03 < nmz787> I haz made downpayment on the excavator
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--- Log closed Sat Dec 11 00:00:57 2021