 Jim Crosiar |
What filter or filters for infra red I have a Sony DSC-S85 and would like to take infra red photos. I already have the adapter for 52mm screw in filters. What infra red filter or filters would you suggest I use?
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John A. Lind |
Jim, The first question is whether your Sony DC can effectively record IR. Although the CCD may be sensitive to IR, nearly all DC's have a "hot mirror" covering the CCD to block nearly 100% of IR. Serious DC IR shooters perform brain surgery on their cameras to remove the hot mirror from inside the camera. This is not for the faint of heart, it obviously voids the warranty, and you may find it declared non-repairable by Sony if you accidentally damage the camera and send it to them for repair. Before buying a rather expensive IR filter, I suggest testing your camera for IR sensitivity first. The standard method for doing this is attaching a "black slide" over the lens front. When developed, a piece of unexposed slide film is almost pure black and blocks nearly all visible light. However, it allows IR through as if it's completely clear. Reason? Film developers often mount the 25th or 37th frame from a roll of slide film, even if it was never exposed. They also throw in leader and trailer pieces of film, much of which is also unexposed. These are not that hard to come by if you know someone who routinely shoots slide films. Developed, unexposed slide film is routinely used over flash heads by IR shooters to make IR flash units that give off very little visible light. The Xenon tubes in them put out a lot of IR along with visible light. With the lens covered by this makeshift IR filter, make some photographs oudoors under bright sun. Green plants in bright sunlight seem to work best for testing. If your camera has reasonable IR sensitivity, the exposure won't be that long and the green plants will look like they're covered in snow. If this test doesn't show satisfactory IR sensitivity, then you either need to get a different DC for IR work, or be willing to perform the necessary surgery on your Sony. This type of surgery renders the camera useless for visible light photographs. It's why they're made with a hot mirror over the CCD. If you do decide to perform surgery on the camera, you do so at your own risk (I'm **not** recommending you do it). The most often used IR optical filters for camera lenses are the 87 and 87C (B+W 092 and 093; Heliopan 780 and 830). The 87 blocks visible light except for deep red. The 87C blocks all visible light. 87 and 87C are the "Wratten" filter numbers, a common numbering scheme. Heliopan's filter numbers are the cutoff wavelength (e.g. 830 nanometers), and I don't know the logic for B+W's numbering scheme. Other filters suitable for IR include the 88A and 89B, although these allow even more visible light than the 87. -- John
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Jim Crosiar |
Thank you for your very detailed answer. I will do as you suggest with the black slide. As for me doing any surgery to the camera no way. I can't afford to buy a new one. Once again thank you, Jim
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