Rick Newton responded to me privately regarding my autofocus questions. He has asked that I forward those messages to SPORRS. Here they are, at his request.
John C. Lucas Date: Thu, 25 Sep 1997 04:20:58 -0400 From: "Rick S. Newton" <[EMAIL PROTECTED]> Subject: SPORRS: SPORRS revisited Sender: "Rick S. Newton" <[EMAIL PROTECTED]> To: John Lucas <[EMAIL PROTECTED]> Content-Disposition: inline X-MIME-Autoconverted: from quoted-printable to 8bit by internet.roadrunner.com id CAA10629 Hi John, I use an EOS-1n and a EOS-1 as my bodies. Although lately I have been using manual focus lately (I have been using a teleconverter that causes unreliable autofocusing), I have used autofocus quite extensively, with varying results. The EOS system uses a phase control something or other that compares the contrast between two separate images to calculate the autofocus. Also in the 1n, of the 5 focus points, only the center is cross biased. In other words, the camera can recognize vertical and horizontal lines in the center focus spot, but only horizontal (or is it vertical, it slips my mind right now) for the other four. First, the in-your-face headlights have a tendency, because of their extreme brightness, to flatten the image, or lose contrast per se. The 1n then begins to fight this, causing eratic focus behavior. With some of the bigger lenses, you can minimize this to an extent by limiting the focus range, which isn't a bad idea anyhow, as there is no need to focus down to 5 feet when shooting a train at 60 mph. Now, two different types of continuous autofocus are available, although you actually only select one, the switch between the two is automatic. First is the normal continuous mode. Any focus spot on the camera will refocus the lens when the object changes distance from the lens. However, with a 60 mph train barrelling at you, when you release the shutter, there is a delay, about 6 milliseconds if I remember correctly, as that info is transferred to the shutter. Then there is mirror travel time before the shutter releases. This is enough time to cause the object to become out-of-focus. Then there is predictive continuous focus. This mode must be started by aligning the object in the center focus spot. Once the camera has been able to determine motion, the camera will track the object across all focus spots, and will "predict" the correct focus of the object at the time the shutter releases. Unfortunately, with the EOS system, the object must be travellin at a constant speed. Any change in speed, and you must again center the object in the middle spot. Here is the trick. Most people will tighten their tripods down rigid, so the camera may not move. For the in-your-face shot, tighten your ball head down to where you can get just enough movement to follow the train a little. When the train comes into view, make sure you get that center spot on something on the nose of the train, (handrails, logo, bell, etc), and keep the spot on that object briefly to allow the camera to "lock-on". The camera should then track the train across the other focus spots, provided they don't get hammered by the headlights. Moving your composition slightly as the train moves will avoid this problem. I know you are going to say that you don't want to change your composition, but, with autofocus, it is a necessary evil. You may also say that you may not want the train centered in your composition, but once the camera can lock on, it will follow the train across the spots With a little practice, you can get it so you can make such minor changes, you will never know the difference. As far as the train not being covered by a focus spot problem, there are two solutions. One, is very similar to the above. Leave your ballhead slightly loose, and slightly move the camera till the train is in the dots, get a lock, and AF lock the focus, then return to your precomposed composition. If the train is small enough that is does not cover one of the spots, you may focus on anyhing near it, due to the lens at or near infinity already. The other way, is to simply prefocus the camera, and apply the AF lock. Autofocus, unfortunately is still not a perfect science. It can easily be fooled, although the manufacturer's are making it much better. But with a little practice, you r results can be fantastic. There is definitley a technique involved, and when you find the niche, it becomes relatively easy to great shots a vast majority of the time. I look at it as no worse than the many times I miss with the manual focus, although it usually is very minor in nature. I am going out on a slight limb, but I still think the EOS system is by far the best. I wouldn't give it up for anything. It takes a little getting used to, but it is well worth it. Hopefully , what I have said here helps. If not, Oh well, you can remove the shoe from my mouth anytime now. Sincerely, Rick Newton Die Hard Canon EOS shooter Date: Thu, 25 Sep 1997 11:22:15 -0400 From: "Rick S. Newton" <[EMAIL PROTECTED]> Subject: Re: SPORRS: SPORRS revisited Sender: "Rick S. Newton" <[EMAIL PROTECTED]> To: John Lucas <[EMAIL PROTECTED]> Content-Disposition: inline X-MIME-Autoconverted: from quoted-printable to 8bit by internet.roadrunner.com id JAA24335 Hi John, Glad some of my experiences (not always good) have been helpful. First on the metering issue, for the most part, you are correct, the headlights and ditchlights throw AE off, sometimes as much as 2 or 3 stops, which is totally unacceptable, especially with AE, because with my experience, AE exposures are already about a 2/3 of a full stop brighter, usually due to lighter colored reflective subjects. There is a trick here also, one that the EOS-1n, and actually I believe any of the EOS cameras, and probably most of manufacturer's as well. That being the one and only AE lock. There is a very easy technique to this, simply, as the train approaches, take a meter reading before the headlights are close enough to affect the meter, lock the exposure. If you are like me, and waste mega film zooming back and firing as the train fills my viewfinder (by the way, I have for the most part abandoned the zooming method), you would notice that you exposure changes as the train size and reflective characteristics change throughout the sequence. AE lock helps prevent this. Alas, unless you suffer the horrible Cohen/Gilley phenomenom, where as the train approaches, mere moments before the shutter is released, a large water vapor filter obscures the sun, and not only is the shot hosed, but the exposure is worthless anyway. Of course this happens when doing incident light metering as well, unless you are superhuman and can take incident meter readings, (and use them), as the train is blasting through your viewfinder. :-) (sorry Dave and Jim). Of course, also using spot metering as well could provide a solution as well, provided the center of you image is what you want to be metering. Secondly, don't feel too bad about the lens situation, I only have 3 as well. 28-70, 80-200, and a standard 50. Unfortunately, my 80-200 is the older version, with the rear element flush with the camera mount. I am forced to use a 3rd part converter 2X for my lens, I cannot use the Canon, which has the front element protrusion. If you have the 70-200, you do not have this problem. However, with the Canon 1.4X converter (as well as the 2X) I understand autofocusing is good, however, it IS slower. This may account for part of your problem. Autofocus cameras typically become somewhat less "perfect" when slower lenses are used, because of the perceived decrease in contrast that autofocus sensors use and that limitation is about f5.6. Manual focus is required beyond that point. I am using a 2X converter on an f2.8 lens, thus an effective aperture of f5.6, thus slow and somewhat unreliable response, thus manual focus is preferred. Using a 1.4X brings it to f4.0, pretty acceptable as far as the camera is concerned, but definitely slower, and a little less reliable. As you learn the system(s), you become accustomed what the system can and cannot accomplish (which you seem to have a pretty good handle on). Even at f5.6, the autofocus can work fairly well for me on a train moving at or near a perpendicular motion in relation to my lens, but I know if that damn thing is barreling nearly head on, ibetter be manually focusing. Of course usually, these things are decided by your composition long before the train ever arrives. Here is another example, when I know I am goin to use the teleconverter, and I have to manually focus, I use the older EOS-1, because the focus spots are not in the way. When not, the 1n is usually the camera of choice. I typically keep the same film in both cameras, so my incident metering is correct when I switch bodies, or are using both bodies simultaneously. I do incident metering as well, except when I am in shade, and the time or distance is too great to walk into the sun for a reading. BTW, I usually only use the 28-70, and the 80-200 plus the 2X tele. I find the 28-400mm range is generally good enough for my photography. Now if I ever get enough money, the 17-35 and a 300 2.8 could be on my horizon though. Rick --> SPORRS: Serious Photographers of Railroad Related Subjects
