OT: Ways to read hidden lettering?

Why not make your own IR camera:

Lots online when you search for "Make your own IR camera"

John :-#)#

I've only tried my hacked IR filter-less camera with IR zappers, not tried to take a pic of anything. I'd not considered adding an IR-pass / visible cut filter, as in that file. I wonder what material that is mase of, polythene? I know that passes the IR of PIR use, whatever wavelength that is. I also assume the IR of such a modified camera without germanium lens is only sensitive to about 1 to 3 micron IR

from

Thanks for posting that link John. It really makes me want to buy another camera to modify. Since I have a machine shop any physical mods and special filter mounts will be easy for me. In fact, I built a filter/lens mount for my Sony DSC-120 Cybershot camera. This has allowed me to mount telephoto and fisheye lenses to it. Eric

Wasn't it you who tried taking an IR filter out of a camera and found that it would not focues without the filter in place? John, posted a link in a reply to your post . The article the link points to says that some cameras will need the IR filter replaced with a piece of glass the same physical size for the camera to work properly. You should read the article. It has some pictures that were taken with various filters that only let in certain wavelengths of IR and blocked all visible light. I can see how this might work for you project. Eric

guilty, that was on a close to scrapper camera, just used as a trial run, not worried if I wrecked it. The current one I've removed the IR blocking filter from, was a thin sheet , not a block of material like the one of my previous posting

Hmmm, those terahertz airport scanners are rumoured to be able to see through clothing, so perhaps they would work. May be difficult to beg, steal or borrow one, though...

Mike.

I wonder how many people had accidently lost their "X-ray" Sony camcorder so they could not surrender it .

You can make an acceptable IR-pass, visible-block filter using a thin piece of black-colored acrylic sheet plastic ("Plexiglas"). The black color is apparently a dye, not a pigment.

I've taken some acceptable near-IR photos using this technique, with an old Canon digital camera whose sensor lacks an IR filter. It requires an exposure of several seconds but it does work.

Find a home inspection company that has a hi res thermal imager at 3 microns or 10 microns. Heat the wall with a heat gun gently and image.

Steve

If you can hack the old tech, IR film (of the roll in the camera, take pictures you can't see, process in a darkroom with wet chemistry sort) might be a way to access near-visible IR photography on a lower budget.

Before you rip out the IR filter, check the camera (or various cameras) with the source - many cell phone cameras (at least) can "see" enough near-IR to show near-IR sources without removing a filter.

Visible light, digital camera and image post-processing MIGHT do it.

Different but similar application with old letters (literary estate) and blacked out parts was sorted by scanning at high color depth and separating brown-ish-black from blue-ish-black as the ink written in and the ink blacked out with were different. Not my project, went to a talk at a conference where it was presented.

John-I got all jazzed up reading the article you posted the link to. Then I looked at some more. Then a little later I made a trip to the hardware store and stopped in the thrift store a few doors down to look for a camera. Dropped 8 bucks and came home with two Cannon ELPH cameras. I don't know yet if eather camera works but for 8 bucks it was worth the risk. Eric

I've just butchered a 3.25" floppy disc and quite a nice sepia tone to the outdoor scene I was looking at it through, not tried on the camera yet.

"photoshopping" I can see has possibilities here as I'm only interested in reading the text , ie differentiatable colour or luminance levels, not pictures of foliage against black skies or anything artistic.

Electrostatic detection apparatus ESDA as used for forensic examination of paper indentations may also be worth investigating as alternative to IR?

piglet

To be honest I think your best bet is to illuminate the scene with filtered longwave IR (and no visible) and use an amateur astronomy CCD camera time exposure to try and image through the wallpaper. How well it works depends on how much pigment is in the wallpaper. The paper should be moderately transparent to IR but the pigments may not be.

These cameras are relatively common and your local astronomy club might well have someone who is game to give it a try. The difficulty is that there is a limit to how well glass lenses transmit IR. The other problem is that you will need to do it with a quality longpass filter as you are in the noise >> signal regime on this one.

The FLIR addon for an iPhone5 would be another option.

Possibly the one with the best chance of success if you don't know someone who owns a genuine FLIR camera.

agreed one of those add-ons or the low res FLIR cameras , but just for a one-off job , cannot justify the prices or even to hire one for one day.

I've now got a test patch of wall with painted on gloss black 3 letters of the right size, will wallpaper over it on Monday.

So does exposed & developed 35mm film.

ITYM *unexposed* developed slide film which is a good cheap IR long pass filter since the dyes block most of the visible light.

Using it for viewing eclipses or looking at the sun can cause serious eye damage since it makes the visible light level tolerable whilst still allowing enough near IR through to cause retinal burns.