Using an Infrared Filter

[arphot]

Hi . . . and long time no be here. Hope everyone's doing OK. I came asking my photography friends about the use of IR filters which I just got for my B-DAY. And, needless to say I'm not savvy in the use of this new item. It's a Hoya R72, Pitch:0.75. Can I be pointed in the direction of the basics? I tried it knowing that I had to use a long exposure (and did; 30 seconds, ISO 100). But, the image came out black. How can I make the best of this filter? I have my Canon DSLR Digital Rebel XT on manual setting. Any help would be greatly appreciated. Thank you. Kirk

[inkista]

I've found that the Hoya R72 with my Canon XT added well over 12 stops (12EV) to the exposure time. I was doing 30 second exposures outside in bright sunlight during the day time in Southern California with iso 100 and f/8. If you're, say, shooting indoors, it's going to take considerably longer. If your shot is coming out black, you're severely underexposed. Keep going. That's what bulb mode and tripods are for.

[arphot]

Thanks inkista. I was shooting outdoors. I will try bulb mode again. I tried a couple shots yesterday that gave some indication that light was getting through. One on bulb setting. I will extend the bulb setting by giving it more time and seeing what results. Thank you for taking the time to respond. Kirk

PS . . . I've attached the resulting image from on of the shoots:
F/22 @ 30 seconds. Fairly bright day, but overcast.

[inkista]

Ok, let's do the math.

If we assume a sunny day and the sunny-16 rule, you can do:

iso 100, f/16, 1/100s as a regular exposure.

If you were using iso 100 & f/22, then as a conservative guesstimate (assuming I'm right about the 12 stops), you need 1/50s+12EV as your shutter speed. (1/50th because you ate up a stop by going f/22).

That's 1/50 * 2¹² = 1/50 * 4096 = 81.92s.

BTW, when it comes to using f/22, you should probably learn about the diffraction effect, too.

I'd recommend using a wider aperture, unless you want to do an extremely long exposure. While a lot of fuss is made about focusing in infrared, if you have enough light, the AF system can actually be quite accurate, since it's looking through the filter.

[LeeR]

Some time ago I took a stab at writing a tutorial, and while the tutorial flopped misreably, there were loads of links there to some of my favorite sites about IR and the people who are doing it. However, in my article I neglected to mention Eric Cheng's fine website and the information he has there. He was, after all, the one who convinced me to give it a try.

[arphot]

Thank you. I shall begin digging on this asap!