nutek
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phidong wrote:
I think the biggest assumption in this thread is that IS for wide angle works and that it is as effective as IS in other lenses.
First off, to understand if it is even possible to put IS into a wide angle lens, we really have to understand how IS works. When you shake your camera like a polaroid pictah, what is happening is that you're shifting the image plane around either up and down, forward to backward or right to left. But how does IS compensate for this? Easy. Theres an element or a group of elements that shifts the image and projects it in the opposite direction. Canon actually uses two sheets of glass on bellow like things that move together or apart at opposite angles. So now that we understand why it works, how exactly does it know what to do?? Motion detectors and gyros.
If anybody has ever owned a primitive IS lens, you've probably heard the advice to turn IS off when you put it on a tripod. But why? The reason is the detectors would shift the elements or IS mechanism in a sin-like motion (back and forth) because they would get confused. Easy fix, if the IS notices that there is little movement or doesn't detect a lot of movement it will switch to a mode where it only worries about the mirror slap.
Wait, did I just say if it detects little to no movement, it switches into a "stanby-sleep like" state? .. I think I did!
So now that we completely understand how and why IS works, why not in wide angle lenses? When you' deal with a telephoto lens with 10% FOV, a shift in the axis where the sensor is is a HUGE shift in the image plane. What this means is that the motion detectors and gyros will NOTICE a shake and compensate for it. That is why people invented that magic 1/focal length rule. The longer the lens, the shorter the shutter speed needs to be to produce an acceptable image.
On wide angle lenses, this is the reason some people can handhold a 20mm lens for seconds. No, I didn't make a typo. SECONDS. Keep in mind I said some people, this doesn't apply to everybody, but most people should still be able to get pretty steady shots even at some slower shutter speeds.
Now, why not IS in a wide angle lens? The answer is right above. The REASON you can hand hold a wide angle lens has nothing to do with it's size and almost everythign to do with the fact that your photographer's handshake has almost a negligable affect on shifting the image plane, basically you don't shift it enough. The problem then is, if I can hold handhold at 20mm for almost half a second (speaking of me now) and get an acceptable image, where the human eye probably couldn't detect shake...
how will the IS mechanism detect the "shake"? You have to ask yourself then, will IS in a wide angle lens be benefitial or detrimental to the performance of the lens? And even if it did help, how much would it help? 3 stops? 2 stops? 1 stop? Would it be worth the extra 500 dollars for people who can already handhold a wide angle lens at for 1-2 seconds? And for people who CAN handhold the lens that long, would the IS mechanism even be functioning during this time, or would it be in sleep mode because the image plane was being held so still? In which case, the photographer would just be carrying around deadweight.
Answer all these questions then make projections of how many people would buy the lens. IS in a wide angle is almost the equivalent of a 1200mm lens. It's cool, but it isn't practical and not everybody needs it. Well, when I say not everybody I mean very few people need it. So when you think about Canon as a business, it doesn't make financial sense to research and develop a product that few people will buy.
And there is the answer to your question.
Edited by phidong on May 01, 2005 at 12:37 AM GMT...Show more →
While I generally agree with your points regarding the business parts of the debate, from an engineering standpoint, your analysis may be inaccurate.
If the said accelerometers can already "notice a shake and compensate for it" for a telephoto lens, then the same said accelerometers will also be able to notice the shake for a wide-angle lens (keeping of course, the "shake" as well as the size and weight of both lenses constant). The resultant image or FOV has nothing to do with the equation.
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But not everyone can do that...
