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Sam's Laser Repair FAQ (repairfaq.org)
122 points by newswasboring 11 days ago | hide | past | web | favorite | 40 comments





This FAQ got me the behind the scenes at a concert.

I'd never owned anything fancier than a Radio Shack laser pointer, but I'd read Sam's FAQ cover-to-cover out of sheer curiosity.

Sometime around 2010, I found myself dropping some things off at a convention, where I was not involved but knew some of the staff. This landed me in a conversation with one of the A/V crew for the dance (happening a few hours hence), specifically the guy who did the laser show equipment. Pretty fancy stuff, especially for 2010.

We end up talking a LOT about lasers, most of which I know from the FAQ, never having touched any of the stuff in the flesh. He takes me down to the ballroom to check out the setup, we play with it a bit, and I'm totally fascinated, not just with the hardware, but the controls that sequence the various show routines. Then he says something like "You seem to have a handle on this.. listen... I never get to GO TO the dance because I'm always back here. You wanna take a shift on the board?", and next thing you know, the lights are down, the fog is up, and the DJ is giving me hand signals to know when to change the laser wibbly-wobbly as he switches songs.

Mid-show, a costumed figure walks up to the board, laser-guy peeks out from behind the mask, "How ya doin? Need a breather?" and I'm like "Nah this is awesome, have fun out there!", and he disappears back into the crowd.


More like unpaid onstage than backstage ;) Awesome though

One of the most useful aspects of this is it's longevity. It's longevity is mediated by the simplicity of the site. It's just HTML and files on a file system. There's nothing to break (except links, which he covers in the introduction). I've been using it for 20+ years.

At this point it's ancient history, but at the point I first came into contact with various electronic bulletin boards (FidoNet, Usenet) in the mid-90s FAQs were a ubiquitous thing. For many topics, just reading the official FAQ for that subject gave you a very good overview of whatever you were dealing with extremely efficiently. I've honestly never quite figured out why we moved away from that as the internet grew in popularity, but it's nice to see at least one relic still exists.

Yep. I probably first read the FAQ in 2005. Still a viable reference; I send students there occasionally.

The links page (remember those?) is a gold mine of high quality ancient internet archaeology. I definitely remember Sam's site from the altdot days. I do miss the sheer quantity of irresponsible electronics that was on the internet 20 years ago. It's been ages since I've seen a furby electrified with the wrong end of a utility pole transformer.

https://www.repairfaq.org/sam/sambook.htm


Laser professionals in both academia and industry frequently use this site as an important reference. It's an immensely valuable trove of information, and not only for hobbyists.

Disappointed to miss "Don't look into laser with remaining eye".

Honestly my favorite website on the entire internet.

The laserfaq is what got my hooked into optics, which sent me down the career path that I am on now.

I owe it all to you Sam


> The laserfaq is what got my hooked into optics, which sent me down the career path that I am on now.

What do you do now?


Quantum computing

Wow. Totally forgot about this. I studied photonics for my bachelors 15 years ago and this was incredibly useful. Everyone in the department knew about it.

Thrawled through this site when trying to understand how stimulated photons knew how to copy the direction of travel of the incident photon as this was the only source of information at the time which did not require a lifetime of commitment to studying quantum mechanics.

I still don't understand it.


My favourite from there:

DED - Dark Emitting Diode


> So the 1 mW laser has the potential to produce an intensity on the retina 167 times that of direct sunlight!

I really don't understand why laser-pointers are even legal.


Depends on the optics. "1 mW" isn't enough information. Focus that down enough and it could burn, but so too can sunlight. It also depends on the time of day. In the dark of night your iris will be open, making a laser much more dangerous. Sunlight is more powerful but as a general rule your iris isn't going to be open during sunlight. A billion years of evolution have made our eyes rather good at handling sunlight. We have no natural defense againse lasers, especially invisible IR lasers. (Stay away from the cheap green lasers from china. They often pump out huge amounts of IR.)

FYI, the general legal limit for "pointers" is 5mW.


Did you read the section on laser safety?

https://www.repairfaq.org/sam/lasersaf.htm#saftoc

EDIT: I read it again and the crux of the matter seems to be this:

> The ability of the retina to dissipate heat is not dependent on the area covered, but the periphery (circumference) of the exposed area! The blood vessels are in the retina and not the sclera (the surface under the retina) - it is the blood flow that dissipates the heat and so can only act on the edge not the middle of the exposed area. In circumference terms, the ratio drops to 7 times. Furthermore because the larger spot is less efficient at dissipating heat, the effective power delivered by the laser beam is only about 2 times greater than that of the spot formed by the sun.


Ya. The cited math is very short, missing many environmental variables.

Lasers safety are also a small part of my job (military). I've got a pile of "pointers" that would blind in an instant, several in the watt-class (ie >1000mw). Anyone can buy 50,000mW laser "pointers" for a couple hundred bucks. I had everyone at work bring in their kid's laser "pointers" a few months ago. Almost every one of them tested above 5mW. 10-20mW was the norm. Assume that everything on ebay/amazon is above 5mW.

I refuse to stay in the same room as a working laser engraver/cutter. They are generally in the 2000-4000mW class, enough for even a slight reflection to instantly create a colour-specific blindspot.


Do you mean 2000 - 4000 watt, rather than milliwatt?

The one I work with is 4000 watt, capable of cutting up to 20mm carbon steel, 20mm stainless, and 12mm aluminium.

It’s fully enclosed with dual electromechanical locks on each door, and an air extraction system with dust and collector.


That one isnt handheld. It isnt part of a 200$ machine being sold to highschools. Danger is always both technical and situational. I did mean mW. A mW-class laser is more than enough to do instant damage, damage that would put an end to a person's career as a pilot.

> They are generally in the 2000-4000mW class, enough for even a slight reflection to instantly create a colour-specific blindspot.

And many of them are IR, so you wouldn't see the leaky beam at all until it zapped your eye.


Yep, the one I work with is 4kW 1070nm.

A typical human eye will respond to wavelengths from about 380 to 740 nanometers.


I just love the old school look of this, but at the same time wish he had a YouTube channel to explain all this.

It would be completely against the point of the site.

I'm surprised it even bothers with HTTPS.


Agreed, I hate YouTube videos for instructional content. I can read much faster than the instructor can speak, I can ctrl+f, and webpages don't tend to pad their content to fill a 12-minute video for 10 seconds of actual content.

My only gripe is that the page's margins aren't a bit more narrow.


Heh. I love no margin design like this. It's a counter to the gratuitous"more whitespace" design foisted on the internet by zealous web designers.

I agree in general, I just find super-wide pages hard to read, and think there's a lot of middle ground between super-wide and "full of whitespace".

Just adjust the width of your browser window to whatever width you prefer and the text will follow. That is, after all, what a browser was supposed to do: show text. If you use Firefox you can also open the inspector and select a mobile view (the two-screen icon top-right in the inspector frame/window) but that is more work for the same effect.

I generally just use the built-in reader view, so it's not really that much hassle, it's just slightly more work. Plus, reader view gets rid of all of the styles on the page, which would be nice to avoid.

Then don't maximize your browser.

It might be too obvious to point out, but.. browser window is resizable.

A long time ago I found most YouTube videos were still completely comprehensible in 1.5x to 2x speed, depending on the exact speaker, and have been watching them at that speed ever since. Not just education but entertainment.

On the other hand, the downside is that you get used to that speed, and listening to people talk in realtime feels abysmally slow. Others may also ask you to slow down more frequently.


I do that with audiobooks as well, and when I set it to 1x speed it feels like the person is speaking intentionally super slow to make fun of the listener, it's odd.

2x is a much better speed, but still, it's annoying to have to watch 6 minutes of video to get the single sentence you want.


The layout's been just like this since last century. It was an appreciated feature when we were all on dialup, and at the time I found readability to be no problem on a 17" CRT monitor (10.5" x 14") at 800x600 resolution.

I can confirm it doesn't translate well to a modern ultrawide monitor.


That's when I just resize my window to flow the text to my desired width. I appreciate having the control in my hands, not theirs.

A lot of videos on Youtube have automatically generated transcripts available via a menu item in the three-dot menu. Once the transcript is opened, you can use your browser's search function to search it.

The problem is that (most) Youtube videos are not people reading a technical document. It is geared toward "speaking" meaning that a lot of information is not covered due to time constraints.

Ymmv with non-US accents.

I love you.

>My only gripe is that the page's margins aren't a bit more narrow.

Agreed, I use a chrome extension 'Just Read' to fix websites that do this.




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