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Old Dec 10, 2003, 8:47 PM   #21
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The lens could back or front focus by itself if it doesn't respond correctly to the (correct) signals from the camera body. For example, if the camera tells the lens to step the focussing mechanism forward 1 unit (whatever the unit is) but it steps 1.2 units, then the lens is wrong, not the camera.
True, but let's deal in integer! ie it's all one and zero after all (data and clock, the other signals are power and ground)! :lol:



If a lens overshoots then the camera should step it back otherwise we're talking about how fine a tuning step a lens should be... IMO they should have optical encoder inside the lens to determine their exact position anyway which are relayed back to the camera.

Bottom line is (and both you and I know), with a few exceptions non-L Canon lenses are not worth having... and in between there's a fine line where some higher end 3rd party lenses which can fit the bill quite well. As you're aware by the postings not all camera owners can afford the L series exclusively... BTW for the record I also have two Canon's: the EF 28-135 IS USM, and the 85mm f/1.2L USM.
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Old Dec 11, 2003, 2:48 PM   #22
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OK boys, you totally lost me on this lens/camera discussion. I'd like to re-focus you (no pun intended) on my December 10 post. I've been to the photo store and like the feel of the Nikon D100 much better than the 10D. Is the quality of both cameras close enough that I should go with what feels most comfortable, or is the Canon so much better that I'll be sorry if I buy the Nikon (which at this second I'm leaning towards). What do you think?
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Old Dec 11, 2003, 4:05 PM   #23
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Come to think of it... may be because of too many novices attracted by the low price of Canon's entry level, but it's relatively quiet on the Nikon board regarding focusing issue... May be you're really better off with a Nikon!

The other comment I have on your other post is the 10D seems heavier to you because it is. The 10D is all metal whereas the D100 is made of Polycarbonate like most modern SLRs including the 300D... 8) It really boils down to lens preference, ie if you like USM/HSM quietness of the speedy AF (or like/dislike the trademark heat resistant white color of the L lenses) and IS there's slightly more abundance on the Canon camp, but the Nikon optics are also flawless...

... regarding the slowness of the display on playback of the 10D, if you zoom in, the display update is considerably faster and remain at that constant zoom ratio so you can actually review the pictures quicker in this mode (ie magnified which is what you want in the 1st place)

Good luck you can't loose either way !
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Old Dec 12, 2003, 12:20 AM   #24
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They are both good cameras, I don't believe you'll be unhappy with either. Feel matters a lot. If you feel the D100 is that much better in your hands then you are more likely to use it. Yes, eventually the 10D would feel good too, but this still matters. I know people who dislike the D100 because itís too light. They are used to the F100 and F5. It just feels wrong in their hands.

Optically, at least to the level of people in this forum, Nikon & Canon are the same. They both make really good lenses, really good coatings and really good housings.

Some AF-S lenses are just as quiet and just as fast as USM. Please, do not give in to the hype that says otherwise. I've used both systems. Some Nikon lenses are dog slow, but Canon makes some slow ones too.

As to which camera to get.... Please, please, please. Evaluate the entire package. Think about which lenses you want and look at the quality of them for each system. Do they even exist? Are they reasonably priced? What about flashes (if you'll get one.) An SLR is a system, so make your decision around that.

When the time came for me to pick between the 10D and D100, the deciding factor was lenses. One of the big ones was the Canon 100-400L. Its a much better lens than the 80-400 from Nikon. Of course, Nikon has announced a 200-400 f4 that (on paper) looks really, really good. Of course, it's really, really expensive. To me the bodies are basically equivalent in quality (at least, in my non-expert hands they would be) so you have to look at other things... like lenses.

As to the Focus adjusting discussion, I'll be brief. NHL, you're wrong. barthold, you are right.

I've read a description of how Canon tests AF issues. The put their own 200 f2.8 prime on the camera body and adjusts it to that. Once that focuses correctly they put your lens on the camera and fix the lens if it needs it. Lenses can have problems just like bodies.

Also, lenses work in the non-digital world. They move physical things, so they are not working in "integers", a lens could be told "move 3 millimeters forward" and instead move 3.3mm (have a .1 mm error per mm.) The analog world is not in integers.

Eric

ps. Do you reall think the non L lenses are that bad (generall)? I own 4 lenses and two are L's. So I certainly don't have the experience to say. That just surprises me.
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Old Dec 12, 2003, 12:42 AM   #25
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I'm using the D100 strickly for my kids high school sporting events and I plan to start with the 28-200mm lens. I'm interested in keeping the camera light weight. As time goes on I'm sure I'll add some better lenses, but I think a $2,000 investment is a far as I'm willing to go right now. I'll continue to use my 7i as a backup and travel camera.
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Old Dec 12, 2003, 9:03 AM   #26
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Eric

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As to the Focus adjusting discussion, I'll be brief. NHL, you're wrong. barthold, you are right.

I've read a description of how Canon tests AF issues. The put their own 200 f2.8 prime on the camera body and adjusts it to that. Once that focuses correctly they put your lens on the camera and fix the lens if it needs it. Lenses can have problems just like bodies.

Also, lenses work in the non-digital world. They move physical things, so they are not working in "integers", a lens could be told "move 3 millimeters forward" and instead move 3.3mm (have a .1 mm error per mm.) The analog world is not in integers.
Am I really? I didn't want to get into this but here we go:

Picture a quartz watch. The second hand can move .8s or 1.2s each step because of the mechanical play (ie in integer), but it's still 60 steps a minute. Now on a wall clock the second hand is longer (ie it move in a bigger arc like the effect of a higher focal lenght), manufacturers would put in a 2:1 gear reduction ratio such that a step is now 1/2 a second, but guess what? The mechanical play is still there so now the error is .4s to .6s with 120 steps... That's just the nature of all designs involving mechanical tolerance and we can play this game by reducing the gear ratio even more. Correct? (which is why some lenses take longer time to focus... ie the more the reduction ratio, the more steps)

Now picture a "Chinatown" special watch which is poorly manufactured and the second hand is @ the 1/2s mark and move .5, 1.5, 2.5s... etc. Is this watch any less accurate than a Breitling which also steps 60 steps a minute but exactly on the second? You guys are thinking in absolute term, but everything is relative. Even if Canon spends all the money in the world and adjust the lens so that when a measurement tape at a specific distance, every step in the lens correspond exactly to 1mm, what if I just go up and relocate that same measurement tape by .5mm (which is what a subject in real life do)? Can you picture it? They no longer line up, what about the effect of a 1.4x/2x teleconverter or +1, +2... etc diopter that we talked about in the other post that anyone can add to their lens?

Go back and read all the postings again. When a front/back focus occurs, the viewfinder is in focus, but the resulting images are not. This means the AF and lens perform flawlessly according to the AF sensor in the viewfinder, but the sensor capturing the image in the film chamber could be out of alignment! It's not an open-loop! The AF sensor sees if the lens has mistep (undershoot/overshoot) and compensates for it properly within the error of tolerance of the mechanical slack of each step; However the film sensor is not on the same path or hopefully the same relative position as the AF sensor after the mirror is flip-up
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Old Dec 12, 2003, 1:51 PM   #27
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I am certainly not knowledgeable enough to argue against what you are saying. I'm saying I've talked with people who have taken their lenses to a Canon certified Tech and watch them do it, and talked to them about how/what they do. They wouldn't waste their time adjusing the lens if it didn't need adjusting. I'd like to think they wouldn't mislead people by writing on repair sheets "adjusted camera body and lens X but not lens Y".

There is something that can be adjusted in a lens.

I don't claim to know why they do it, as you'd pointed out my logic could be wrong. But they do do it. You can choose to believe me or not... I believed the people I talked to.

I've also read of people who claim that it looks in focus in their view finder but then the picture isn't. (This isn't front/back focus, obviously.) I can't explain this one, and I never heard the resolution. But I wonder... is that the body or the lens? No idea, really.

Eric

ps. My camera mount seems to be having problem so I'm going to have to get it checked/fixed. I wonder if I can get them to test my lens at the same time and talk to them while they do it. Now that could be fun.
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Old Dec 12, 2003, 2:50 PM   #28
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Eric

This an illustration of how an AF is supposed to work, but I don't want to post it because the info is not correct for the 10D since this camera does not have a 1/2 mirror but its AF sensors are behind the viewing screen in the prism. My point is the focusing path is different from the sensor path (ie 90 degree), and the sensor can be located slightly ahead (backfocus) or slightly back (front focus) from the film plane which is what need to be adjusted... -> The picture comes up sharp in the viewfinder (ie the AF works just fine), but the image is out of focus on the image sensor since it's distance relative to the viewfinder is different from what you see (and what the AF sensor detects)!

Now on to the lens mount: When you attached a teleconverter you obviously change the distance and insert a bunch of correcting elements in between the lens and body. Does a teleconverter need to be adjusted as well? NO! (how about correction +1, +2 closes-up attachment in front of the lens? NO). Whatever is in front of the camera will be treated the same way (wear and tear on the lens mount included), and compensated for accordingly. The AF mechanism will go and back and forth until it finds perfect sharpness in its phase detectors just like anyone would on manual focus by judging from the viewing screen. The problem has always been that the image is seen as in-focus but the captured pictures are off focus because the detecting image sensor is not on the same plane as the AF sensor -> one of the two sensors need to adjusted so they both come in perfect alignment!

Think about what you guys are writing how can anything focus on a fraction of a millimeter? Look at the marking on the lens barrel... it's engraving is in meters! One would need a micro-Vernier scale to move the focusing ring in order for it to be accurate to even a few centimeters (Or draw two lines 1mm apart, and see if the AF can detect a difference, vs two more lines 1mm apart, but placed 1cm away from the 1st pair)!
http://www.a1.nl/phomepag/markerink/af_expla.htm
http://electronics.howstuffworks.com/autofocus3.htm

... Now internal glass elements to the lens can shift with time (or displaced by dropping)... Internal screws holding a lens element can get loose, but theses are all different. This is the time when a lens need to be adjusted... ie it's not performing its function, this is a lens defect not AF error. You can see theses problems (and so do the AF sensors) in the viewfinder such as a corner is always out of focus, or one can't achieve focus, up close, far away, or not at all (and again the AF will try to compensate if it can)!
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Old Dec 13, 2003, 11:43 AM   #29
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This is from a Nikon post I just made, but the questions are the same if I get the 10D--

Regarding a lens for my 10D or D100, how about the Tamron 28-300mm f/3.5-5.6? It has the same f-stop as the Canon/Nikon 28-200mm and the camera store told me that it's rated very well. Will this work as well with a lens and body from the same company would? Does anyone have any ideas? Also, is there a website that analyzes these different lenses?

By the way, the assistant manager, who shoots sports all of the time, told me I should seriously consider the Olypmus E-1. He said it's faster, shoots 3 fps for 12 shots, has a great 50-200mm lens (which at a 2 times multiplier is 100-400mm f/2.8-3.5!), and has on-the-fly white balancing. I still think the 10D/D100 is the way for ME to go, but this sure sounds interesting.
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Old Dec 13, 2003, 2:31 PM   #30
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Oops, the Tamron 28-300mm goes to f/6.3 at full telephoto NOT f/5.6. So would I be better off with the Nikon 28-200mm f/3.5-5.6?
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