Infra Red Flash And Focus Assist Questions

metroeloise · 09-30-2008, 06:39 AM

Learning about photography and my k20d is quite an adventure. It leads me into many different paths. Recently I read about the use of infra red flashes. In the longer term that interest includes getting a dedicated infra red camera. In the short term I came up with this idea:

When I shoot at music shows in the local pubs-bars I often want to turn and take crowd shots. The people right up front are often dancing and make for good pictures. I have the fa 50mm. I also don't wear my glasses since I just use them to read. Well then and to focus! Since the Pentax struggles in the dark I find myself selecting manual focus and simply guessing. That is not good enough at f 1.4! But I don't want the flash going off. Not even for the chirping it does to focus assist. (I have used it that ways then close it for the shot) So how about using a piece of developed film as a flash filter?

Figure it could "see" the now mostly infra red assist flash while my friends dancing wouldn't notice it above the bar stage lighting. Would this work? I figure I would close the flash after I got focus or then again leave it on. So would it add to the exposure?

Musing these questions at work. Dug through my old film prints and found a strip of exposed and developed film. Off to experiment! But first: Is it safe? I wouldn't want to the film heat up too much and stick to the flash. I'm figuring on fashioning a slip on sleeve with the film on the end.

Thanks for reading.

flyer · 09-30-2008, 10:29 AM

I don't think a piece of developped film could act as an ifra-red filter. It could be used to filter the light in a way, but not necessarily infra-red light.

*Damn Brit* · 09-30-2008, 03:00 PM

These might help Eloise, they were done by our very own Codiac2600
YouTube - K10D: Bar/Nightclub photography tips PART 1
YouTube - K10D: Bar/Nightclub photography tips PART 2

Let me know what you think of them.
If they don't cover what you need, maybe check Codiac2600's web site, he mentioned in a post yesterday that he has quite a few tutorials on there.

metroeloise · 09-30-2008, 04:45 PM

I'll head on over there at work tonight if all is quiet. Just received my monopod and that'll help.

Originally Posted by Damn Brit

These might help Eloise, they were done by our very own Codiac2600
YouTube - K10D: Bar/Nightclub photography tips PART 1
YouTube - K10D: Bar/Nightclub photography tips PART 2

Let me know what you think of them.
If they don't cover what you need, maybe check Codiac2600's web site, he mentioned in a post yesterday that he has quite a few tutorials on there.

As for the use of film for a infrared filter? Anybody know? I'm also bringing the material with me to work and make me up on to see.

metroeloise · 10-01-2008, 04:15 AM

Tried my experiment with using a piece of exposed film as an infrared filter over the built in flash while it is chirping in focus assist. Tried at various distances and it doesn't work. I'm going to give it one more go with the 50mm opened up close up.

The film reduces the visible light to a point that it is not annoying, one goal. Would a piece of a "real" infrared filter work where this didn't?

Another use I can see for this, in addition to focus assist, is in triggering digital slave off camera flashes without adding to the exposure.

Back to the drawing board! Need to find me an infrared filter!

RioRico · 10-05-2008, 11:08 PM

Exposed film makes a lousy IR lens filter. You want to filter visible light, get a real IR filter, available for as little as US$20+s&h on eBay. I've read of folks modding a flash for IR by wrapping exposed film around it, but that's flaky, and your stock camera probably won't notice. Sigma and Fuji make IR-native dSLRs; your Pentax will need a mod. Scan these forums for INFRARED for more info.

I dearly love my old Sony DSC-V1 5mpx NiteShot PNS, which has great IR sensing and a limited-range IR light source. I've added a Sony HVL-IRM light source (US$20+s&h on eBay) for more range. If you want to shoot action in the dark, you need the right gear. Be aware that almost any digital IR images will be grainier than the same image in visible light.