using built in flash as IR transmitter

[jon_sak]

I have a nikon 8700 and a couple of slave triggers (plus 2 vivitar

283's. I don't want to buy a IR transmitter or a SB series flash for

it. I was told that I could use developed slide film as a way to

block visable light and still trigger the slave flashes. I am sure it

will work, but I threw away all my ruined slides, my question is will

negative film work also or something else?

[garry edwards]

Jon,

 

Technically correct answer, you want to put a #87 infrared filter gel over the flash.

 

Technically incorrect answer, any red lighting gel over the flash will do.

[Bill C]

And technically, a more direct answer to your question is, "Yes, processed color negative film will also work." Use a couple pieces of dmax film (the processed black leader, for example).

 

For whatever reason, organic dyes in general seem to have a hard time blocking the near infrared. I can't give you any references, and the published film curves (dye density) don't seem to show beyond about 700-750 nm wavelength, but I think they've all died off (that was a pun) by ~800 nm. So any C-41 type film should work.

[sauerwine]

I'm not familiar with the 8700, so I'm not sure if it's got a hot shoe, but I think I'd go this route, if you're only looking for a trigger. I thought of this because I wonder what side effects would show in your shot, if any...

Get a yardsale flash. Crack it open, remove the strobe tube, and replace it with an IR LED. You'll have to wire resistance (at least) into the circuit, but anyone somewhat familiar with electronics can tell you values to use for sure. Boom. $10 or less for parts, and you have an IR transmitter...I think. Yes, the other method is cheaper and faster, but this transmitter should trigger just as fast and accurate as the other. For that matter- you could install three of them on your donor flash, one on the front, and the other two- one per side. This way, you could trigger at right angles to your camera position.

 

Incidentally, there are schematics out on the internet for a device called an "infrared repeater." This will receive IR signals, and trigger another IR receiver which may be out of the line of sight of your original sender. (Used mostly with stereo equipment which is behind dark glass or inside a cabinet, when the user wants to control with the remote without having the doors hanging open.) The schematics are detailed, but if you can handle a soldering iron this might send you down the path of making your own IR equipment. I mention it because its just another possibility- maybe not the best. The filter method will send your IR bouncing all over the studio, so it may work just fine for your purposes.

[jon_sak]

Thanks Bill C. it works exactly liked I expected. By placing the exposed negative film over the Nikon 8700 pop up flash only the IR light triggers the slaves. Therefore I can use My Vivitar 283's on a slave. Bu the best part is the anoying pop flash does not inerfere with the picture. I am excited and as for building my own IR transmitter, thank you for the advice but thats more work than I was willing to do

[sauerwine]

Hey....fool I was for not catching the "built in flash" part of your subject line! Ehhh....it was late. Sorry!

 

I'm glad you got the [other] answers you did, though- they'll come in handy for me and others.

[john_sack]

Well, my name is John Sack, but I shoot Canon and have an ST-E2 transmitter...:))

 

Original post:

 

jon sak , dec 14, 2004; 02:47 p.m.

 

I have a nikon 8700 and a couple of slave triggers (plus 2 vivitar 283's. I don't want to buy a IR transmitter or a SB series flash for it. I was told that I could use developed slide film as a way to block visable light and still trigger the slave flashes. I am sure it will work, but I threw away all my ruined slides, my question is will negative film work also or something else?

[joseph_wisniewski]

Be careful using color negative film for this. Two reasons. First, the orange mask absorbs a bit of IR, believe it or not, so you get less transmission.

 

Second, color neg film melts easier. Slide film, they choose the base for projection, minutes of high intensity light. Print film is chosen for its ability to lay flat, it's softer. For the onboard 8700 flash it's probably not critical. If you try ro filter something like those 283's, neg film will curl after a few full power pops. (so will Wratten 87 gells, and those are expensive).

[steve_hovland]

When using on-camera flash to trigger slaves, if I can't tilt the flash, I just hold a business card in front of it to keep the light off the subject.

 

Sometimes I use a small piece of Rosco Rolux diffuser to have some fill from the camera flash.