Something else I’ve noticed but isn’t widely reported is the loss of acutance with the same lens compared to its visible-light performance, especially as you go out from the center of the image. Notice the distinctive bluish spot at f/16. The left frame was shot at f/4 and the right frame at f/16. ![]() This is from my hot-spot test of the Sony FE 24-240mm f/3.5-6.3 lens at the 35mm focal length. Or hot spots may not appear at wider apertures but show up as you stop down (example below.) With zoom lenses, you may get hot spots at some focal lengths and not others. Some lenses don’t exhibit hot spots at all and thus are preferable for infrared. ![]() Hot spots are usually bright areas in the middle of the image and tend to get worse and more defined as you stop down. The most common issues or problems that show up with infrared that you won’t see in the same lens with visible light photography are “hot spots”, loss of acutance (sharpness), and sometimes excessive flare.
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