Re: AF Performance (Was: Re: Opinions about 80-200 f2.8 zooms)
Monday, November 8, 2004, 12:39:45 AM, Alan wrote: AC Many people have reported some Sigma lenses took longer to lock focus (tend AC to hunt more). It seems that the distance and focal length data are required AC for AF as well, and those data are held by a chip inside the AF lenses. Probably. I had problems with a Sigma 1.8/28 (the old version, not the EX one) in Nikon mount, it consistently frontfocused. On several bodies. I previously thought that impossible, but apparently there is now so much chips in lenses and cameras that even what looked like a closed loop system (check focus, rotate by some computed amount from FL and distance, recheck focus) can get buggy. But it was from a period when Sigma lenses were quite buggy. Nowadays, they make the software in them better I heard. Good light! fra
RE: AF Performance (Was: Re: Opinions about 80-200 f2.8 zooms)
So which is responsible for the AF performance? Is it the lens? the camera? or both? and how does each influence the AF performance? Inquiring minds want to know Both. Some AF lenses have lighter and smoother AF mechanisms might AF faster. Some AF bodies have stronger AF motor might AF faster. Some AF bodies have better algorithms might lock focus and track moving subjects better. Alan Chan http://www.pbase.com/wlachan
Re: AF Performance (Was: Re: Opinions about 80-200 f2.8 zooms)
So which is responsible for the AF performance? Is it the lens? the camera? or both? and how does each influence the AF performance? Inquiring minds want to know Both. Some AF lenses have lighter and smoother AF mechanisms might AF faster. Some AF bodies have stronger AF motor might AF faster. Some AF bodies have better algorithms might lock focus and track moving subjects better. Good answer. I could not have said it better. (Actually, I could not even say it that good, but that's another matter... - g) Fred
Re: AF Performance (Was: Re: Opinions about 80-200 f2.8 zooms)
- Original Message - From: Larry Cook Subject: AF Performance (Was: Re: Opinions about 80-200 f2.8 zooms) So the answer is that the camera possess the algorithms for AF but the performance is based both on the algorithms and how responsive the lens mechanism is? If that is correct then a lens that seems to hunt more than another is not directly at fault? It is the camera algorithms not being able to adequately handle the responsiveness of the lens? Interesting. Of course you would still want to avoid such a lens because it is the system as a whole that is important and therefore an unresponsive lens that causes the camera to hunt is still a bad thing regardless of which component is actually at fault. Unresponsiveness or hunting can be induced by a variety of external factors that have nothing to do with the equipment, as well. Trying to focus on a low contrast subject that gives the AF nothing to latch onto will cause hunting. Low light levels will cause hunting, and this problem will be exacerbated by a slower lens. Some third party lenses won't work as well with some cameras as first party lenses. Consumer market equipment may not be a responsive as pro market equipment. It isn't possible to get a camera/lens combination that will perform 100% flawlessly 100% of the time. I think it is a good idea to focus manually whenever auto focus isn't required. This way, you will have that skill in place for when you need it. William Robb
Re: AF Performance (Was: Re: Opinions about 80-200 f2.8 zooms)
I understand that circumstances can stymie focusing but what I was concerned about were reviews that talk about a particular lens' inabilty to focus well or that it hunts more than another lens. Currently I have all manual focus lenses and I am trying to determine if an AF lens would be better to photograph my son's soccer games and sort of veered off into how AF works. Larry Cook So the answer is that the camera possess the algorithms for AF but the performance is based both on the algorithms and how responsive the lens mechanism is? If that is correct then a lens that seems to hunt more than another is not directly at fault? It is the camera algorithms not being able to adequately handle the responsiveness of the lens? Interesting. Of course you would still want to avoid such a lens because it is the system as a whole that is important and therefore an unresponsive lens that causes the camera to hunt is still a bad thing regardless of which component is actually at fault. Unresponsiveness or hunting can be induced by a variety of external factors that have nothing to do with the equipment, as well. Trying to focus on a low contrast subject that gives the AF nothing to latch onto will cause hunting. Low light levels will cause hunting, and this problem will be exacerbated by a slower lens. Some third party lenses won't work as well with some cameras as first party lenses. Consumer market equipment may not be a responsive as pro market equipment. It isn't possible to get a camera/lens combination that will perform 100% flawlessly 100% of the time. I think it is a good idea to focus manually whenever auto focus isn't required. This way, you will have that skill in place for when you need it. William Robb
RE: AF Performance (Was: Re: Opinions about 80-200 f2.8 zooms)
Many people have reported some Sigma lenses took longer to lock focus (tend to hunt more). It seems that the distance and focal length data are required for AF as well, and those data are held by a chip inside the AF lenses. Alan Chan http://www.pbase.com/wlachan So the answer is that the camera possess the algorithms for AF but the performance is based both on the algorithms and how responsive the lens mechanism is? If that is correct then a lens that seems to hunt more than another is not directly at fault? It is the camera algorithms not being able to adequately handle the responsiveness of the lens? Interesting. Of course you would still want to avoid such a lens because it is the system as a whole that is important and therefore an unresponsive lens that causes the camera to hunt is still a bad thing regardless of which component is actually at fault.
