Infra red flash / lighting?

[TrabimanUK]

Hi guys,

I'm looking at getting my 40D converted to IR so that i can get some nighttime snaps on animals on safari next year, as we're doing a couple of night drives and for obvious reasons can't use white light. I've found a couple of reputable companies in the UK that can do the IR conversion, so that's nice and easy. The only tricky part is the lighting side of things, as it all seems to be pretty expensive.

I'm a bit weight limited on the trip, and some of the IR "lights" are quite heavy even thoug they are LED. As such, I was thinking of converting a flash unit. I have found some IR-transmissive perspex that only lets IR light through, and was thinking of getting a Yongnuo 560, taking out the clear lens and substituting it for a matching peice of IR transmissive perspex, thus giving me an IR flash invisible to the wildlife, but not to my camera. I appreciate the YN560 isn't ETTL, and that's not as problem.

I appreciate that I will lose some light, and I'm expecting the wildlife to be circa 20m away.

Any thoughts / suggestions on if this is a good idea, if anyone can recommend an alternative or a good supplier of cheap IR lights that have a 20m+ range?

Huge thanks in advance,

Grant

 

[Loswr]

What you suggested seems like a great option, and basically what I'd have suggested. Personally, I'd 'gel' one of my 600EX-RT flashes with a longpass filter, either a commercial filter sheet or unexposed developed slide film.

You might consider adding a Better Beamer for more flash reach with longer lenses.

 

[Max ☢]

I second Neuro in saying that filtering the flash with an IR-transmissive filter is a great idea - xenon plasmas such as those generated in flashtubes have a peak spectral emission between 800 and 950nm, which is great for the IR exposure of silicon-based detectors. Krypton tubes are even better in this respect, but I doubt that you'll ever find such flashlamp for photography (they’re commonly used for optical pumping in certain lasers though).

One issue that might arise is the proper illumination of your subjects because of distance (obviously) and of the narrower band of the "spectral matching" between your light source and the sensor combined with the optical filtering. If the first case can be solved simply by using the proper collimating optics on your flash, the second issue is more tricky to solve because it has to do with the fundamental nature of the xenon source and of the sensor as well as of the IR filter you use.
First of all, check the transmissivity curves of your filters and choose the one which is the most transparent in the spectral region of interest. Next, in order to maximize the overlap between the spectral sensitivity of the sensor and of the spectral emission of the flashtube, choose the filter with the cut-off wavelength closest to the visible domain - e.g. a cut-off at 750nm will be preferable than one at 800 nm.

If with all that you can’t get the right exposures at the desired subject distances, then the last resort is the use of narrow-beam halogen spotlights combined with IR filters. The tungsten filament in the common automotive halogen lamp runs at over 3000 K, giving a peak spectral emission at around 960 nm, which is also great for IR photography (such solution is actually commonly used for large-area CCTV illumination at night. If you’re by car, then this solution should not be a problem given that 12V halogen projectors are a cheap commodity.

As for LEDs, this technology is great in that it provides a narrow band spectral emission and the emitted light can be easily focused into a tight beam. The main issue is that the amount of emitted optical power is quite limited, especially compared to the brutal halogen lamp.

 

[TAF]

Modifying the Yong is a great idea; xenon strobes put out a large amount of extra energy in the IR range (UV as well).

By removing the original lens and replacing it with the IR filter, you'll get maximum IR output (the original plastic lens is at least partially intended to absorb the "undesirable" IR and UV that the strobe naturally generates).

It would be interesting to compare a filtered 600EX with a modified Yong, and see which generates more IR power.

 

[TrabimanUK]

Hi,

thanks for the comments and ideas. I can't quite stretch to a 600EX at the mo - would love to, but it is way to pricey for me, but I'll go ahead with the YN-560 conversion and report back, hopefully positively and in the not too distant future!

cheers guys, much appreciated!

Grant