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Ask Slashdot: Are Progressive Glasses a Mistake For Computer Users?

iliketrash Notes from an old hand (464 comments)

I’m going to be as brief as I can. I could write pages on this topic. Buying progressive lenses twice over a few years has been the worst retail experience of my life. The dispensers are like clothes salespeople and other retail stores: get the customer out the door as fast as possible. Unfortunately that didn’t suit my style and so I had to become my own expert. I won’t write generally but will try to address your specific problem.

I have scanned the earlier comments and didn’t see all that much that is useful to you. (Sorry, other posters, I said _scanned_.)

First: There are _hundreds_ of progressive lens designs, and probably thousands of patents. Most dispensers have found that they have a decent success rate with a particular design; for all I know, they might have a bulk rate from a manufacturer. If the lens does not suit you, take them back and ask for another design. Any respectable dispenser will tolerate this—they won’t love you, but they will tolerate it. On my first go-round, I had four different designs, but then the lab screwed up at least one or two.

Some designs are quite crappy. There has been a lot of progress in lens design in the last 10 years. Some lenses are still designed by an old buy who remembers Zernike polynomials and does his work with a pencil and paper. You don’t want these. Get a modern lens design known as digital progressive lenses, high definition, HD, or more commonly, free-form. These designs are made using a computer and divide the lens up into “pixels” where a performance goal is met subject to an overall cost function. The in-between-points are probably interpolated with a cubic spline. You see, the problem with lens design is, if you try to make it better in one place, it gets worse in another place. This is why it is an interesting design problem. The modern, free-form designs are _far_ better than the old designs. Some designs actually allow precise measurments to be made on your frame _before_ the lens is made; this information is sent to the lab and incorporated into the lens design, essentially a custom-made design. Shamir comes to mind, but there are others. At least one company has a slick jig for an iPad and an optical splitter that fits over the iPad’s camera so that even a monkey could set this up without screwing things up. (FYI, be prepared to deal with monkeys.) The free-form designs can trade off near, intermediate, and distance regions that you can select depending on your lifestyle. Many new free-form designs excel at getting a wide channel, which is to say, the intermediate, which is great for most computer work. Free-form designs are much better at getting the near vision wider. My current lens is a free-form design and it is _far_ better in both intermediate width and near width than my old conventionally designed lenses. (FWIW, my current lens is the best Seiko lens, and I recommend them.) And you will also find that there are “computer glasses” which you should consider; these have giant intermediate and near regions and pretty much punt on distance.

Many dispensers will bitch and moan if you get a short lens (frame); these became fashionable 10+ years ago and still are. That’s bullshit. They will try to put you in an “old fart” frame because they claim that it forces fewer compromises on the design. Then they will take your prescription and increase it so that it is more powerful at the bottom of the giant lens so that it is correct at the near vision region that you actually use. You simply can’t rotate your eyeballs far enough to see to the bottom edge of a giant lens.

Getting the frame adjusted (bent) is critical for progressives. The optical axis has to be aligned with the optical axis of your eyeballs. The lenses come from the lab with a fitting cross or dot on the lens. If you get your new lenses and do not see the fitting cross, your dispenser has removed it. Ask them to put it back on. They have a simple tool to do this. The fitting cross should be directly in front of your pupil when holding your head normally and looking at a distance. You won’t be able to see the cross yourself but they can; or you can look in a mirror to satisfy yourself that it is correct. THIS IS IMPORTANT! The nose pads can be adjusted to raise or lower the fitting cross. Two other parameters are important: the pantoscopic angle and the wrap angle. The pantoscopic angle is the angle that the mostly vertical lens makes with the front of your mostly vertical face—look at your profile using a double mirror. Most designs are intended for about 10 degrees. This is a little hard to measure yourself but you can eyeball 10 degrees. Your dispenser should bend the frame for you; in my case, I had to learn how to do this myself. Obviously if you have plastic frames this isn’t always an option, so word of advice: get metal frames. Best, get three-piece frames. The wrap angle is how much the frames wrap around your head. Imagine looking at your head from above and observing how they seem to wrap around, or match your head shape. Getting this set as much as you or your frames can tolerate will enormously help the global distortion (not focus) that you see. Demand that this be be adjusted or do it yourself. (Bending metal frames is not rocket engineering. Get some needle nose pliers and pad it with a thick wash cloth to avoid marring the frames. I have titanium frames—Marchon 720—and they are great to work with and indestructible.) Overall, get the frames as close to your eye as possible, as this also reduces global distortion. (Contacts are zero distance and have zero global distortion.) I set mine so that my eyelashes gently brush the lens when I’m laying on my back, face up.

Pay for optical obsorbing coating. This is a worthwhile add-on, as it greatly reduces all sorts of anamolous reflections. This is kind of cool—it is seven or nine layers of optical material of slightly different index of refraction, sputtered on the lens in a series of quarter-wavelength absorbers. Pretty neat, and really effective. And if you get rimless or monofilament-attached lenses, don’t get the edges of the lenses polished—polished edges reflect overhead lights and sunlight like crazy and you will see these annoying reflections all the time in such lighting. Get the dull finish. The dispenser will try to tell you that the polished edges is cosmetically better but screw that. I have pretty thick lenses and nobody has ever said my unpolished edges look uncool.

The vast majority of material used for lenses is polycarbonate. This is the hard, tough plastic that Compact Disks are made of. That’s fine if the only thing you’re going to shine through them is a laser (single wavelength) but for the octave or so of visible light, polycarbonate is the _worst_ material there is. Why? Because is it seriously dispersive. That means that the speed of light (and the index of refraction) is dependent on the wavelength of the light. And polycarbonate is the worst. Really. There is a crude but common and effective measure for this phenomonem called the Abbe number. Polycarb’s Abbe number is 30. A resin known as CR39 is outstanding with an Abbe number of 60, which I think is also the Abbe number of crown glass. The so-called high-index materials are pushed by many dispensers. They tend to have also crappy Abbe numbers and are not nearly as strong as polycarbonate but they are popular because the lens can be made very slightly thinner. So if you don’t care if you go blind when your car’s airbag goes off in your face, get a high-index lens. Otherwise, there is a good compromise: Trivex. Some manufacturers re-name it, but it’s still Trivex. It is as tough as polycarbonate but has has intermediate Abbe number of 45. I forgot to mention why dispersive materials are bad—they act like prisms for anything off the optical axis, and the further off, the worse. I mean, they separate colors into their spectral components. Not cool. This will bother you especially in high contrast scenes such as nighttime signs or reading in bright light. You will actually see the color fringing. Just get Trivex and be done with it.

You declared your use very clearly. Your choices are progressive including “computer glasses", lined bifocal including so-called executive or Franklin bifocal which extends the “line” across the entire width of the lens which I think you should seriously consider, or a single-vision lens that you wear only for computer work, but if you need correction for computer work then you also need it for reading and other close stuff. Your choice depends on if you are OK with removing and replacing your glasses during the day and carrying them to restaurants etc. versus how you tolerate multifocal, progressive or conventional. But—a single-vision lens will work just fine for your use (but your dispenser won’t make as much money off of you). And you should know that adapting to progressives can take a while. Give it at least three weeks. You will be surprised what your brain can adapt to especially if you have never worn glasses before. But seriously, a free-form design will be easier to adapt to compared to an old-school progressive design.

Oh yes—you will not find _anyone_ who is an expert on comparing all of the available designs, but some dispensers are more concerned about learning this information than others. I don’t know how you find them. I found tons of useful information on the discussion lists at optiboard.com.

So there. I believe I started out saying that I would be brief. :-/

about a month ago

Stack Overflow Could Explain Toyota Vehicles' Unintended Acceleration

iliketrash Use Ada (664 comments)

"How can users protect themselves from sometimes life endangering software bugs?"

Use Ada.

about a year ago

Google Chrome 32 Is Out: Noisy Tabs Indicators, Supervised Users

iliketrash Why does anyone use this spyware? (141 comments)

Do any Slashdot readers use this spyware, and if so, why?

1 year,14 days

Red Hat Releases Ceylon Language 1.0.0

iliketrash YABL (159 comments)

Yet Another Brace Language

about a year ago

Ask Slashdot: Best Cross-Platform (Linux-Only) Audio Software?

iliketrash Flamebait (223 comments)

Why are you such a Linux retard? You're killing yourself creatively by asking for this kind of of software for Linux. If you really want to explore your musical creativity you need to get the hell off such a limited platform. OS X and probably Windows platforms are far, far better as far as choices in this field. Yea, there is Adaucity which you're already found is a piece of crap, or would have discovered had you not limited your world to Linux. And Ardour—nice work, but that's about it. Do yourself a favor and let your creativity flow by looking outside the extremely limited options offered by Linux.

about a year ago

KDE Releases Calligra 2.7

iliketrash Calligra web site is uninformative (30 comments)

The Calligra web site is incredibly bad—there is almost no information about any of the programs, just a few superficial paragraphs. Just awful, an embarrassment to the development team, I'm sure.

This is an example of the "airport signs" problem: The people who build the airport already know how to get around the airport and so the signs that they put up are not helpful to those who rarely visit the airport.

On another crappy note, the link to the OS X installer just goes 404.

Oh well.

about a year and a half ago

Camping Helps Set Circadian Clocks Straight

iliketrash Then three days later, it's back to normal (173 comments)

Right. Then the person gets back from his/her happy little camping trip and back into his/her normal life and three days later he/she is back on the same stupid schedule. I've done this many times and camping is not necessary—any outside influence that causes one to rise earlier will do. I didn't read the article but it sounds really stupid to me, so I won't.

about a year and a half ago

Fidus Writer: Open Source Collaborative Editor For Non-Geek Academics

iliketrash Re:Google Docs CAN DO LaTEX (160 comments)

Well, this does look interesting. I played with it for 15 minutes and: I can't think of anything worse than writing anything of any significant length inside a browser. This bypasses all of the hard work that my OS provider (Apple) has spent for decades polishing a decent user interface. As far as I can tell, everything has to be done using the mouse/trackpad—no keystroke shortcuts.

Also, compiling even the short sample document is excruciatingly slow. There is an option to use my local TeXLive installation but the radio button to select it was disabled. If one really wants an easier-to-use LaTeX editor, there are free ones that also provide one with menu-selectable math items.

about a year and a half ago

Things That Scare the Bejeezus Out of Programmers

iliketrash My biggest fear: C (641 comments)

"What's your biggest fear?"


about a year and a half ago

Mozilla Launches Initiative To Adapt Scientific Practice To the Open Web

iliketrash Scientists did not create the web (28 comments)

"Scientists created the web"

No—_engineers_ created the web.

about a year and a half ago

One Week With GNOME 3 Classic

iliketrash Why doesn't Linux use sub-pixel rendering on text? (169 comments)

The screen shots from https://live.gnome.org/GnomeShell/Tour show that this interface is not using sub-pixel font rendering. I have noticed this on most if not all other Linux-type screen shots. Apparently the favored font rendering method on Linux is the old-fashioned "treat every pixel as some shade between the font color and the background color". The characters so rendered are substantially less well-formed and harder to read. And this surely isn't a matter of intellectual property: https://www.grc.com/cleartype.htm.

about a year and a half ago

First Looks At Windows 8.1, Complete With 'Start' Button

iliketrash Woohoo! Multiple windows side by side! (800 comments)

"It'll also be possible to have multiple windows from a single app so that, for example, two browser windows can be opened side-by-side."

WFT? Is this for real? Was this not possible before? Surely the implication of this statement that this was not possible before is wrong.

about a year and a half ago

Dao, a New Programming Language Supporting Advanced Features With Small Runtime

iliketrash YABL (404 comments)

YABL. Come on, people, really?

Unsafe arrays.

Forced-indexing into arrays.

Not interested.

about a year and a half ago

Schneier: The Internet Is a Surveillance State

iliketrash Delete your cookies (333 comments)

It's my understanding that tracking is done by cookies. I delete all cookies 2-3 times a day, and always after logging out of Google (which I rarely log in to) and Facebook. The only downside is that I have to log in to again to certain sites but that is easy because of OS X's built-in password manager.

about 2 years ago

Is Code.org Too Soulless To Make an Impact?

iliketrash But Al Gore invented coding (384 comments)

Al Gore may be a politician, but after all, he did invent coding.

about 2 years ago

New Bill Would Require Patent Trolls To Pay Defendants' Attorneys

iliketrash US tramples property rights again (196 comments)

The United States government tramples property rights yet again. Slashdotters love it.

about 2 years ago

Microsoft Could Earn Billions From Office For iOS

iliketrash Microsoft Office as "productivity software" LOL (188 comments)

Calling Microsoft Office "productivity software" is hilarious. I know we've all spent hours trying to do the simplest things with Office. I recently spent nine hours including querying a forum and Googling trying to figure out how to get Word to number equations. Nine hours, and all I got was a clumsy work-around. And I know this is the "right answer" and that I didn't miss something.

about 2 years ago

Ask Slashdot: What Practices Impede Developers' Productivity?

iliketrash Strong typing (457 comments)

Strong typing. LOL

about 2 years ago



"Uncalibrated touch-screen" votes Chicago-style

iliketrash iliketrash writes  |  about 3 months ago

iliketrash (624051) writes "A touch-screen voting machine in Chicago suburb Schaumburg has been found to repeatedly convert votes for several Republican candidates into votes for their Democrat counterparts. The problem has been blamed on a "calibration error of the touch-screen on the machine.” Of course, Chicago has long been notorious for voting hijinks, mostly of the Democrat flavor.

Do touch-screens need such a gross calibration, or for that matter, any calibration at all? If so, what are the chances that an uncalibrated screen would reliably convert all or several votes for one party into votes for the other party?"

Link to Original Source

Global Warming or Recedin Crust? Tiny Island Gone.

iliketrash iliketrash writes  |  more than 4 years ago

iliketrash (624051) writes "These articles announce the disappearance of tiny New Moore Island (aka South Talpatti) under the waters of the Bay of Bengal. An expert blames it on rising sea level due to global warming. Could be. But consider that the island is said to have once reached 2 meters above sea level. Sea levels are said (by the same expert) to have risen 5 mm/year since 2000 and 3 mm/year before that. That means that the island's elevation was mapped 650 years ago, in 1360, a tenuous claim at best. Also consider that volcanic activity and plate tectonics are constantly make new and higher mountains. Unless matter is being created out of nothing, the material making up new mountains has to come from somewhere, which means that the earth's crust has to be falling someplace, possibly many places.

This story appears to be appearing in various media as solid evidence of global warming. But isn't is possible that the Bay of Bengal is sinking? Or that the sea level is rising at the same time? It seems to me that uncritical analysis of data which "obviously" supports a foregone conclusion is the hallmark of groupthink.

[Editor: I can't figure out how to set links to the two articles referenced by "These articles." The links are: ]

PLplot notes its 10,000th commit

iliketrash iliketrash writes  |  more than 5 years ago

iliketrash (624051) writes "From the PLplot development team is the announcement of their 10,000th commit: PLplot is a cross-platform software package for creating scientific plots that has been in continuous development since its inception 17 years ago. On May 23, 2009 the PLplot developers quietly celebrated our ten thousandth commit since our initial software repository was populated back in May 1992. This longevity puts PLplot in some select company amongst open-source software projects. We may even be unique within this group because all PLplot development has been done by volunteers in their spare time. The enthusiasm for PLplot development continues; we have averaged more than 100 commits per month over the last year which is double our 17-year average, and we are looking forward to the celebration of our next ten thousand commits!"
Link to Original Source

Remote home monitoring

iliketrash iliketrash writes  |  more than 6 years ago

iliketrash writes "I plan to be away from my home for a few weeks in the near future (address not included) and would like to provide a bit of in-home monitoring while I'm away. Presumably I will continue to continue to use it after I return. I would like to be able to perform monitoring from a remote web browser with no special features (Internet cafe or a laptop). I can dedicate an old laptop (OS X, FWIW) to the in-home task. Note that the laptop can run Apache (since Apple provides it with every computer). I would like one or two low-frame-rate cameras or, better, motion-activated cameras. Also, I have an aging air conditioning (cooling) system and given that the daily high temperatures in my area of the U.S. can easily reach 110 degrees Fahrenheit, I would like to be able to monitor indoor temperature. There is a secondary situation where I would like to be able to monitor a particular aspect of part of the AC unit which could be accomplished by a video camera if it responded to heat i.e. infrared. (I understand that IR response is common in some video cameras). I have a home WiFi net that could be useful for connecting to the local computer. Of course, I would like it to be cheap. Are there any inexpensive sensors of these types, preferably WiFi enabled, that can be read by a remote web browser?"


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