Back to the IR light source concept...

Okay, I may or may not know an awful lot about either electonics or optics, but I'm a darn good model builder. One of my pet projects is to build a plastic model of every car I've owned and in the process I've learned a lot about handling plastic. To make a long story shorter, I've learned how to take a lucite windshield from a plastic car model that's been "ruined" by having glue run onto it and to repair it into something that's at least as good as new.

Go to

and look for a polishing kit. It has abrasives -- I can't call them sandpaper anymore -- in grits ranging from a low of 2400 up to 12,000. That's right, a grit equivalent of Twelve Thousand! You can make your plastic as "transparent" as you want with sufficient elbow grease and one of these kits.

Norm

Yikes!!!! That sounds like it's probably at least as fine (if not finer) than what an ancient (1906 original publication date - my copy is a 1963 reprint edition) book I have on optics calls "100 minute emery" - As in, "shovel raw, screened emery powder into a 12 foot tall, 3 foot wide pipe full of water, stir the everlovin' bejeezus out of it for half an hour, then let it stand undisturbed for 100 minutes. At the end of 100 minutes, drain off the liquid (catching it - it's the part you want) to about a foot above the bottom, dumping what remains in the bottom back onto the "raw material" pile, evaporate the liquid you drained in whatever way works, and sell the powder that remains after the water is gone as 100 minute emery". As of the publication date of the book, that was apparently the finest abrasive that could be had, and was right at the limit of being practical to "sort out".

I'll hit this "Micromark" place and see what they've got that would suit my shoestring budget. Thanks for the suggestion!

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under

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abrasives -- I

up

IIRC, they sell a full polishing kit with 3"x5" sheets, individual ~6"sq sheets, and a set of roughly 2" dia polishing pads. For most things I use about every other grit, though I've been known to use every one for a really critical job. They're best used wet but you can get a completely different effect using them (mostly) dry. I think that the full set is ~$20 and probably the best place to start. After that, if it's not smooth enough, you can use the Novus-brand of liquid polishing compounds to get an ultra smooth shine. It's probably not something you need for this application.

Norm

I have to say, what you have thought of, using black CDs...is absolutely brilliant, and Ill be trying it myself. Kim

2004.

the

I have never found any economy in building what I can buy. Just takes to much time. You can buy inexpensive IR gells from which you can cut out what you need. Look for a low pass gell at about 750nm. A cheep way is to process a sheet of unexposed slide film if you need a large piece. Or take some of the ends from a processed roll of 35mm or 120 slide film. You can layer them if you need it darker to visable light. Performance wise though, it is going to be hard to beat a real IR illuminator like what is use on night vision devices. Oh by the way, all CCD sensors are sensitive to IR (down to 1300nm) light. All you need to do is to remove the camera's high pass filter and replace it with a clear to IR glass. I have been playing around with a CCD digital camera with a Hoya R72 (720nm low pass) It is an Olympus 2020 and I am comparing it to Kodak HIE film with the same filter. The film is about

5 st> Some of you may recall my post a few weeks ago asking about IR LEDs,

HAH! Cheapest IR-pass filters I was able to find, whether gell, plastic, or glass, are *WAY* beyond my budget for this sort of tinkering. Besides

- Doing it myself is (A) Entertaining (B) Educational and (C) a fun challenge. (Hmm... maybe C should read "both of the above?")

Performance is secondary to price. A "real" illuminator with any kind of range is, like buying the IR-pass filter, way outside my budget, even with the idea of going for the cheapest available.

Replace "all" with "most", and I'll buy into that last statement. Some of them are very IR sensitive. Others barely notice IR at all, while still others are effectively totally blind to it. Depends on the maker and the process they used. External pre-filtering obviously effects the accuracy of that statement...

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Is unexposed but developed scrap slide film beyond your budget? Perhaps you just need something to keep occupied with. Like polishing old CDs.

The CCD sensors are before they place a high pass filter in front of it which is why I suggested to remove the thing and replace it with clear glass to preserve the focus. Which is just what Sony does for their night mode. The lever moves the high pass filter out of the way. But now they also strap the aperture wide open when you place it in night mode. So if you use it in the daylight with an IR low pass filter the sensor saturates.

Ahh, I get it... post a response so you can make a snide remark. FTR, it's my time to do with as I please, so you can take your snotty commentary and shove it where the sun don't shine.

Wasn't that little addition (cranking the aperture wide open in "night" mode) in response to the "Oh my god! If it's used that way in daylight, it's able to take nude pictures of clothed people!!! Oh, the horror! It MUST BE STOPPED!" garbage that started flowing when somebody actually tried it?

I guess saturating the sensor would do a good job of stopping such things... A picture/footage isn't worth much if it's just a white-out.

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Just as a note- if you are removing aluminum based reflective coatings (virtually all of them!), then never never scrub them off with abrasives. Dip them in ammonia and it will dissolve the aluminum right away, leaving the plastic pristine and perfect.

Cheers!

Sir Charles W. Shults III, K. B. B. Xenotech Research

321-206-1840

Excellent idea. But what about "breaking the glaze" of the coating over top of the aluminum? Doesn't seem to me like ammonia will be very effective on aluminum it can't get in contact with...

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Have you tried (in other words it probably won't work, but you never know) aplying a water based clear varnish to the ground side. If the refractive index is similar enough to the plastic (tinted polycarbonate I would guess - normal polycarbonate has n~1.56) and you can get good coverage right into the grooves (you might need to dilute with water) AND you get an even layer it might be good enough - it's light delivery, not imaging that you're after. Underdriving the bulb will increase the amount of IR at the expense of vis as previously mentioned, so perhaps the bulb from a 4 or 6 cell maglite would help as well.

Chris

(p.s. google has given me 1.37-1.48 for refractive index of varnishes)

Not an actual "varnish", but the transmission DID seem at least somewhat better during my "pre-testing testing" - before I managed to get all the

40-weight washed off the piece. I was kinda half-considering trying to shellac/varnish/clear-coat the thing in hopes of filling the scratches, but haven't really made a lot of progres on the idea since the initial "feasibility study", due to being handed yet another fistful of "hot irons" to add to my "fire".

Another couple of options I've pondered, but haven't really gone anywhere with so far are flame-polishing (before I try that, I'll need to do some playing to figure out if it even *CAN* work for this material) and coats of beeswax (Got plenty of that available, for nothing more than the effort of going out to the hive and pulling a frame...) or perhaps a beeswax/alcohol mix similar to varnish/shellac.

This is clearly going to end up being one of those "ongoing project" projects - As I've got time, ambition, and materials, I'll probably tinker with it on and off for the next year or so, until I either get bored, or get it to what I consider "done enough".

Counterintuitive...

I don't see an underdriven filament putting off a larger *ABSOLUTE* quantity of IR - Rather, I see the relationship between mount of IR and visible output changing - As in the IR output stays (nearly) the same regardless of voltage, but the visible component falls off with the voltage drop until the point where visible output is nearly nil, but the IR output is just as strong as ever.

That's not much different than running a filter - No net increase in absolute brightness, but a relative increase in IR output compared to visible. At some point beyond that (exactly where, I'm not sure, but I

*KNOW* that point MUST exist) the IR output is going to start dropping along with the voltage.

The "increase IR versus visible output" concept is good. But how does dropping the voltage *INCREASE* the actual IR output? Or is it as I say above - namely, the IR radiation stays (pretty much, and only down to a certain point) the same, but I don't have to "work so hard" to remove the smaller amount of visible light to get near-pure IR?

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Some modern automobiles use a plastic headlight assembly that 'fogs' with age.. some fog fairly quickly. Inexpensive kits are become available to polish the plastic lenses back to clear.. if the scratches aren't too deep on your lens, this might work for you.

Search on fogged headlight lenses... here's one product..

Hope this helps..

Jim

I'll try and model this and get back to you - but if it's battery driven (i.e. if you really want to use the maglite) it will improve battery life.

Chris

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You're probably OK, if you want to go through the ritual of
never-ending polishing, but there _are_ commercially available
polishing compounds out there which might make your life easier.

Check out

http://www.noscratch.com/novus/index.shtml

Or, you might want to go a completely different route and use an
acrylic designed specifically for the purpose.

Cyro Industries has infrared transmitting acrylic, "ACRYLITE GP" with
a color # of 1146-0 which ought to work for you.  Check this out:

http://cyro.custhelp.com/cgi-bin/cyro.cfg/php/enduser/std_alp.php?p_sid=rANE2Bih&p_lva=&p_li=&p_page=1&p_prod_lvl1=4&p_prod_lvl2=6&p_cat_lvl1=%7Eany%7E&p_cat_lvl2=%7Eany%7E&p_search_text=1146-0&p_new_search=1&p_search_type=3

for spec's.

Well, the whole point of this concept is a portable unit, so battery power is probably the only reasonable way I can go. Nothing says it

*HAS* to be a maglight - that was just my "proof of concept" whack at the problem - but it probably will have to be battery powered to make it practical/portable.

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Hmmm... that one has possibilities, though I cringe at the idea of how much $$ it will take to get ahold of the stuff... When looking at IR-transmitting photographic filters, I was routinely spotting prices in the $150-$200/6 inch square range for plastic filters - Which is why I ended up going with a "make-do" chopped out of a black CD-R. Even the gell filters (which are very likely to have *VERY* short working lifespans) to transmit IR were ridiculously priced - a 70MM round was tagged at $89, fergawdsake! My budget (which is mostly imaginary, practically speaking) for this project can't even CONSIDER those kind of prices! And glass? HAH! If I can't afford the "cheap" gells and/or plastic, then I don't even need to consider glass, since that seems to routinely be about 130-200% more expensive than the corresponding plastic filter.

Now to see if I can find someplace that will tell me how much this "Acrylite" stuff costs... I note a glaring lack of any reference to pricing for it at the link you posted. Most often, I've found that situation to be a red-flag for "If you need to ask "how much?", it's more than you can afford. Have a nice day, and don't let the door hit you in the arse as you leave." materials.

Still, now that I know the stuff exists, I might be able to find someplace that sells it in reasonable quantities, at reasonable prices. More investigation is in order, obviously...

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I modelled the blackbody curves in excel, and you're right, by quite a margin - I don't know whether the power requirement or the IR output would fall faster for a given emitter as you drop the temperature (assuming temperature control for convenience) so it might not even save battery life.

The maglite could be a good way to go - the focussing output would seem to help, even if you have a diffuser effect from the vis blocking filter.

Did you ever try multiple visible gel filters - these tend to be cheap (I seem to remember £10 (~$18)/sq foot), and for a maglite even offcuts would be enough, so even cheaper if you have a friendly theatrical/DJ supplies shop that does stage lighting. e.g. Lee filters

"Blood red 789" transmits only

1% visible in the far red, combine with (e.g.) "Bray blue 722" should do it. I found my old swatch book recently (since the last thread) so I can have a look with a lamp and digital camera later. With anything less than hundreds of watts they'll last forever.

Chris

Nice to find out that the numbers match my world picture :) Seriously! I was having a hard time swallowing the idea that IR output would increase (in any way other than relative to the amount of visible light) due to a voltage drop.

Indeed. I'm thinking that no matter what the raw light source ends up being, whether a "pure IR" source without filtering, or a filter system in front of a visble source, it will be mandatory to have a variable-focus beam.

That has been suggested, but at this point, I've done nothing with it. At the very least, it seems to me that it would be worth trying.

Hmmm... maybe it's just me and my misinformation, but I've always been under the impression that gels are the "cheap to buy this one, but expensive as hell in the long term due to needing frequent replacement" solution. My limited time "on the boards" (credited in the program as "Soldier with a line" - ) in a 6 week run of Jesus Christ Superstar at a local playhouse showed me a lighting guy *CONSTANTLY* griping about needing to chase up into the flys to replace gels - sometimes before each run of the show, and particularly the reds. From that, I reached the conclusion that gels are, at best, a "make-do", rather than a permanent solution. And the prices... At one point, I overheard him saying something like "There goes another hundred bucks" while he was working on cutting a blue one to shape.

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