Dan's Data letters #157
Publication date: 21 December 2005.Last modified 03-Dec-2011.
I'll hook you up, man
I've been a fan of your site for years - love the letters section. Time for a simple question for you. I have a cheap (very slow) "Uniross" branded charger for my batteries. I have a heap of AA NiMHs, varying in capacity up to 2300mAH. I am looking for a good charger that can charge them relatively quickly, and have some sort of smart logic so not as to fry them (a discharger may be a good idea too if possible). I have read that Maha chargers are good, but I cannot find any that will work in Australia (they are always overseas models, for 110V).
Robert
Answer:
I suggest you go to the Maha Energy site, type "Australia" into the search
box, and become Enlightened.
To the best of my knowledge there's still no Australian reseller for Maha products [UPDATE: Now there is - Servaas Products], but because most (all?) of their chargers run from 12 volts with a plug-in power cable, all they have to do is swap the plugpack to make them compatible with weird sockets like ours. It wouldn't be hard to find a suitable plugpack locally, but you don't have to, because Maha sell various chargers with an Oz-compatible plugpack (and often also with a car cigarette lighter adapter cable), and they ship all over the world.
An MH-C401FS like the one they sent me for review ages ago, which I shamefully never got around to reviewing but still plug at every opportunity because it definitely is an excellent product, will currently cost you $US59.95. That includes eight 2.3Ah AAs, which makes it quite a good deal if, of course, you actually need the batteries. Delivery to Australia is $US25, payable via the usual credit cards, so the total is still quite reasonable.
[Servaas Products still sell the C401FS, too; as of the start of 2008, it's only $AU59.95 plus delivery!]
You don't, by the way, need a discharger. Don't get me started.
Zorch!
Because of your sagely knowledge on all things geekish (and then some) I decided a gander at this outfit.
It ought to be worth your while, if even for a laugh. Now, I don't have much of that book learnin' 'bout them thar electrons and such, but something tells me a pair of AAA batteries are not powering a 125mW laser the size of a pen. I have a paltry 10mW green laser made as a gunsight and it appreciably drops in brightness/battery voltage if it's left on for more than about five seconds, and it's powered off a pair of beefy three volt CR123A lithium cells.
Moreover, something tells me a laser the size of a pen driven at 125mW isn't going long without cooking itself, even if it did suck that much juice.
Real or malarkey?
Robert
Answer:
No, AAAs are probably not adequate to the task. If it was just a 125mW load from two AAAs then it wouldn't be that
big a deal - 125mW at three volts nominal is something in the vicinity of 42 milliamps, which is not a light
load for an ordinary alkaline AAA cell (PDF datasheet), but isn't
a whuppin' either.
Green laser pointers, however, are a diode pumped solid state (DPSS) design; they get their light from an 808 nanometre (nm) IR laser diode, well out of the visible range. That light goes through a none-too-efficient two-step converter. First, a neodymium-doped yttrium vanadate ("Nd:YVO4") crystal that converts the light to even-more-useless 1064nm infrared. Next, a potassium titanyl phosphate (KTP) sliver doubles the frequency, finally giving the 532nm green beam - which is pretty close to the approximately 555nm green to which human eyes are most sensitive, which is why green lasers look so much brighter than red lasers with the same output power rating.
The yttrium vanadate has to be there, because directly frequency-doubling the 808nm light (if it's actually possible; I'm not sure if it is...) would give 404nm, which is right at the edge of human visibility at the violet end of the spectrum. 404nm makes all sorts of things fluoresce quite enthusiastically, though, so I reckon there'd be a market for the pointers, until of course some tit started taking advantage of their near-invisible beam and trying to blind people with them.
Speaking of which, there's an infrared filter in every green pointer, to catch any IR that leaks through the frequency converters. If you want to turn a green pointer into a Nasty Device, you can take it apart and remove the filter and the frequency-diddling bits. Re-collimating the laser (getting a beam out of it instead of a spray) will probably be a bit challenging, and the vast majority of people daft enough to try all this will just screw up and break the thing anyway, but in theory you can end up with a high powered invisible laser that'll damage people's eyes very effectively, since an invisible beam doesn't trigger the blink reflex, pupil contraction or looking away.
Anyhoo, a "5mw" green laser with two AAA cells is likely to draw about 280mA from its batteries when they're fresh - which they won't be for long. Higher rated pointers don't draw extra current proportional to their output rating; the people who "make" them pick the best pointers from batches of 5mW units and tweak the crystal alignment, as well as goosing up the actual diode power, so a "50mW" pointer is likely to draw less than half an amp. A "125mW" pointer, if genuine, is likely to still be well below an amp. But a few hundred milliamps will beat the heck out of AAAs in short order; you won't get the initial brightness for very long at all.
NiCd or NiMH AAAs could drive a super-powered module, but there could still be significant cooling issues.
With bigger batteries, though, the sky's the limit. A flashlight-sized casing gives plenty of room for a big heat sink, too. See the "Master Windu..." letter in this column - and don't miss the video clip on this page!
United Nuclearity again
Found this and thought of you (super magnets at the bottom of the page).
"If you really need unbelievably powerful magnets, here they are. Uses include magnetic steering of nuclear particles in homemade accelerators, levitation devices, magnetic beam amplifiers, scrap iron separators, etc."
Paul
Answer:
People keep e-mailing me about United Nuclear's magnets, for some reason, even after they scored a mention in
this letters column.
Really big NIB magnets used to be quite hard to find; these days you can get them all over the place (I think this is the home of the most terrifying assemblage of such items currently offered to the general public), though you probably don't want to. They really are absolute buggers to work with, and pretty much impossible to play with, unless your day job involves wearing a Spandex suit and leaping tall buildings.
Huge NIB magnets can be very useful to people making their own electric generators, though. The unprecedented field strength of these now-quite-affordable magnets makes it relatively easy to convert things like old automotive disk brake assemblies into electrical generators.
Steps 43 to 907: Solder LEDs in place
You wrote about LED case lights, and you wrote about the Canon 20D. I'd like to see you put the two together and write about LED-based lighting options for photography - a homebrewed version of this.
Joseph
Answer:
Litepanels look like quite interesting products. The trouble is, I'm not
into motion picture making, and these things are of very little value for still photographers in general, and digital
still photographers in particular.
Take Litepanels' impressive Ringlite, for instance, which draws 7.2A at 12V at full power and therefore consumes 86.4 watts. I don't know how many LEDs there are on it (because Litepanels don't appear to believe in providing anything so crass as proper specifications), but I can believe that they're not being badly overdriven. As usual, the quoted "100,000 hour" lamp life is likely to be an overstatement, and is in any case the manufacturer's specification before the LEDs dim to 80% (usually), not before they die. The LEDs may shift in colour annoyingly (for film-makers) long before then. But the Ringlite LEDs probably will last more than long enough for most people's purposes.
The more important problem is that at four feet, the brighter 3600 Kelvin version of the Ringlite (which is rather yellow - perhaps it's got amber LEDs mixed in with the whites), running at full power, scores 143 foot-candles over its presumably quite wide beam angle. I'm guessing it's got the 50 degree angle of the "flood" versions of the smaller Litepanels, though once again, that has to be a guess, owing to the absence of comprehensive specs.
Anyway, 143 foot-candles is 1539 lux, assuming there isn't something screwy going on with calibration factors. The 50 degree Mini Litepanel at full power scores a lousy 130 lux at four feet according to the brochure here. Or, of course, less if you dim it; being able to dim the light without changing its colour is a big plus for LED illuminators over various other technologies, definitely including filament bulbs, but it's not much of a consolation if the light isn't bright enough in the first place.
A single dirt cheap super-wide-angle 500 watt halogen "garage light" has a brightness of about 2100 lux at four feet. Focussed down with a better reflector to the same angle as a "flood" Litepanel, it'd be 3000 lux, easily.
You don't want to carry a 500 watt worklight around on your camera, of course. And cheap halogen light is also quite yellow, probably a bit below 3000 Kelvin colour temperature. So you have to put a blue filter on the lamp if you want to match the colour temperature of even the 3600K Litepanel light (or use a much more expensive high-K filament lamp, or some kind of arc lamp, blah blah). The filter will eat some efficiency, but still leave you with 500 watts of lovely heat being pumped into your set and onto your electricity bill.
But digital camera users don't care about the colour of their light, as long as it's all the same. It's the work of a second to white-balance a picture, as you take it or in post-processing. People shooting TV shows on DV cameras can, of course, also do post-production colour control, though in a lot of situations there are multiple colours of light in the scene, and they therefore have to use a nice bluish light when, for instance, filling shadows on an actor's face as they do a tracking location shot on an overcast day. Lighting anomalies can be edited out too, but that isn't a ten-second process.
And, while the colour temperature of a light for digital still photography isn't very important, the Colour Rendering Index (CRI) is important. The lamps have to have broad spectrum output - they have to radiate light at all visible frequencies. It's OK if a given lamp radiates a lot more down at the red end than up at the blue end - that's a low colour temperature, which white balance can fix - but your lighting mustn't have any gaps in its spectrum that'll make things that match those missing colours of light look weird.
This is why normal fluorescent lights don't cut it for many technical lighting purposes - apart from flicker problems, the best household fluoros only have a CRI of about 85, while the really high lumens-per-watt tubes are down around CRI 60.
More advanced fluoros, though, certainly can be had for film-making purposes these days. I'm sure someone makes a smaller on-camera version; it'd be more fragile and cumbersome than a Litepanel, but it'd also be considerably more efficient.
Filament lamps, by definition, have output that pretty closely matches a "black body" curve, with CRI of 100 - a perfect score.
Litepanels don't say anything about CRI that I can find, but it's possible that they're using top-spec LEDs with a CRI up around 90, which is good enough for all but the freakiest of users. I guess if they were using CRI 70 LEDs, someone would have mentioned it. Then again, I dare say that TV show makers (and a lot of movie makers) also don't actually care much about colour rendering - heck, a lot of shows glory in everything being tinted blue or something, these days :-).
Many still photographers aren't that fussed about CRI either - but if you're charging fortunes for your lighting products, you really ought to at least mention it.
It's also possible that Litepanels' claim that their 5600K heads are "three times as efficient as conventional lamps" is true, since it's now possible to get LEDs with double the lumens per watt of ordinary halogens. I don't think any of those LEDs have a CRI of 90, though, so I suspect that the figure's based on a comparison with tungsten filament lamps with blue filters on 'em to bring them up to 5600K.
I agree with you that a similar product could be made for a lot less money - judging by the prices of even the smaller kits, there's a lot of room for alternatives, and a bunch of Luxeon LEDs would bring the array complexity down to the point where you could solder it up without going mad. But for still digital photography, there's just not a lot of point to doing it. If you want cool lighting then use flash or high-CRI fluoros; otherwise, save money and use cheap halogens.
All that said, I can believe the testimonials from the big names on the Litepanels site, regardless of the fact that they no doubt got their Litepanels for free. A nice even light with no diffuser needed, one less thing to go wrong, nobody burning themselves or melting bits of set, et cetera. The things are presumably also built to last - as they'd bloody well better be, for the money.
Camera warranty does not cover crumbs and shavings
Check it out! Pringles cans aren't just good as WiFi antennas!
Kevin
Answer:
As numerous people have pointed out in the other places where this has been
posted, the ingredients list should actually
be "less than £1 worth of equipment, a little bit of sweat and tears, and a
$US75 lens..."
What's actually being made here is an extension tube. It isn't a lens - it just moves an existing lens out away from the camera, thus allowing it to focus closer. This certainly is a cheap way of making an extension tube, but you can buy configurable extension tube sets (allowing several extension settings depending on which tubes you use; you can click the tubes together, too) new on eBay for maybe $US60 delivered. Macro tubes are all optically the same, since they have no glass in them - all they have to do is be straight, and non-reflective on the inside.
The better commercial tubes ($US130 from a place like Adorama) also pass through the autofocus and auto-aperture contacts. Autofocus isn't very useful for tubed lenses (it just doesn't work with more than a small amount of extension), but you need an all-manual lens on the end of a home-made "dumb" tube if you want to be able to stop the lens down for reasonable depth of field without using the suggested, somewhat alarming "use DOF preview, and take the lens off the camera while you hold the button down" technique.
I talk about tubes on the second page of my photo tutorial.
Ommmm...
I am sure you have come across the Global Consciousness Project before, and would love to know your thoughts on it.
Craig
Answer:
It's a
whole bunch of nothing.
Actual scientists are such wet blankets, aren't they?
The GCP grew out of similarly unimpressive research by the Princeton Engineering Anomalies Research lab, which has been failing to set the world on fire for ages.
If people can influence random number generators - or, indeed, anything - by sheer force of will, then even if the effect does seem to be minuscule, it'll be profoundly interesting. Nobody looking at a lodestone sitting in a little boat in a bowl of water and feebly turning to point approximately north-south would, after all, have suspected that investigation of what was going on there could, along with research into the pointless little sparks you got when you rubbed amber with a cloth, lead to the countless miracles of electric power. So it's worth investing some effort in finding out if alleged "psi" effects are real, even if they don't seem to be very impressive.
People had, however, already been trying to find psi effects for a long time before Leonard Nimoy started doing voiceovers for crummy documentaries on the subject. Cost/benefit analyses break down when people have been beavering away at an idea for decades and still have to beat the crap out of the data to make it look as if it supports their hopes and dreams. If the possible benefit is very large, but the chance that it actually exists clearly very closely approaches zero, you'd be better off spending your time trying to catch leprechauns.
Regrettably, so far as anybody has actually been able to scientifically determine, people who say they have psi abilities are mistaken at best and scumbags at worst.
