While the IS function is usually used with slower shutter speeds in low light situations, it can also be switched on when higher speeds are utilized. The minimum is 1/15 sec. with this lens but if you are shooting at 1/125 or 1/250 sec., you can leave the IS mode to compensate for any movement, especially if your hands are not steady enough for hand-held photography. For normal subjects, just set the IS feature to Mode 1 and to Mode 2 if you are shooting moving subjects using the panning technique. The EF 300mm f/4L IS USM lens also accepts 77mm filters or accessories just like its non-IS version and its overall length is slightly longer by 7.5mm at 221mm. Just how effective does the IS function work? The photos shown below are some of the examples of the effectiveness of the Image Stabilizer function of the lens. Bear in mind that the images you see here via your PC or Macintosh monitor may not show the difference between a blurred shot and a sharper photo due to the resolution factor of the screen. Race driver with IS off Race driver with IS on Car door with IS off Car door with IS on Shot with IS off Shot with IS on Since the film used had an ISO speed of 100, the shutter speed at the maximum aperture opening of f/4 only allowed me to shoot at 1/30 sec. hand-held. At 300mm, to get a reasonably sharp image is dependent on how steady one's hand is. Sometimes, I can be steady and at other times, I can't. In this case, the IS function took care of the problem and I just concentrated on the composition. Depending on your monitor, you should be able to see some amount of softness and motion among the four sequence shots shown above. The event was the 1999 Proton Merdeka 300 Km Endurance Race held at the Sepang F1 circuit. << Back to Main . 1 . 2 . 3 .