When learning to see infrared imaging possibilities, the first thing you should do is forget everything you know about light. That’s because everything you know about visible light is wrong when working with infrared images.
Since exposure meters are not sensitive to infrared light, it’s difficult to calculate exact exposures but that doesn’t mean you can’t try, especially with digital camera’s LCD screens providing instant feedback. Two subjects that seem equally bright under normal (visible) light might reflect infrared radiation at different rates and exhibit different brightness. Therefore it’s a good idea to bracket a series of three to five different exposures until you see where the best exposure may be.
Tip #1: Bracketing, if you are not familiar with the term, means that you make several photographs of the same scene, increasing (usually the best bet for IR capture) or decreasing the exposure with each additional frame. Some digital SLRs cameras an auto bracketing function that makes a specified series of shots at exposures over and under what is considered “normal.” Because every camera’s a little different, read your camera’s manual for specific directions.
Even if your camera doesn’t have bracketing function it should have an Exposure Compensation feature that lets you adjust exposures in one-half or one-third (my preference) stops while shooting in automatic exposure modes. If all fails, most digital SLRs offer a Manual mode. You don’t need a hand held exposure meter to get started. Typically I just look through the viewfinder (of an IR converted camera) in Program mode and see the suggested exposure, then transfer that shutter speed and aperture to the camera after it’s set in manual mode and then bracket on the overexposure side until I see the white foliage is clean and bright on the LCD screen
Tip #2: Just because you don’t have a converted IR camera doesn’t mean you can’t use all the tips covered here with cameras that are IR capable out of the box. It does mean that when using dark (you can’t see though them) filters you will probably need a tripod because of the long exposure times produced.
Tip #3: Focus first when using filters, then put the filter on the camera. Usually I just hold it there with my fingers during the exposure or have somebody else, as Mary is doing here hold it, which is just another reason a tripod comes in handy.