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#1
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Focus discrepancies in Rebel XT and XTi, manual and auto focus
I have noticed the most puzzling and disturbing focus discrepancies in
both my Rebel XT and my XTi. Please do the following tests with yours (and please report back!): Set your camera on a tripod Set up a scene with some sharp black-on-white writing in the center Set your lens to auto-focus and press the shutter button half way down until the lens focuses Adjust your eyepiece dioptric to your eyesight Shoot a picture at wide aperture (f2.8 will do) Now, without disturbing anything, set your lens to manual focus Move the focusing ring to dislodge the previous focus setting Re-focus carefully on your viewing screen (do not re-adjust your diopters!) Shoot a picture at the same f-stop Now upload your pictures to your computer and compare the two side-by-side by enlarging the center to the maximum (try "actual pixels" with Photoshop) I've repeated these tests with every conceivable variation of lenses, cameras, with glasses and without, with additional supplementary diopter correction lenses, etcetera. INVARIABLY, the picture done in auto-focus is right on, but the one done manually shows a pronounced focus shift! You can readily see the difference in sharpness between the two. I sent the XTi to Canon and it was returned with the same problem, after thorough "inspection and adjusting". What is going on? Do you see the same discrepancies in your own tests? |
#2
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Focus discrepancies in Rebel XT and XTi, manual and auto focus
Rita Ä Berkowitz wrote: Bob G wrote: I sent the XTi to Canon and it was returned with the same problem, after thorough "inspection and adjusting". They didn't find a problem since this is normal. If that's the case it's a shame. I can't really believe it. Do other brands show the same problem? And why is not this a problem with film auto-focus Canon SLRs? Or is it? And why isn't there a warning anywhere in the instruction manual? I personally like to set my lenses to manual focus, I hate to press a "hold" button and refocus if I don't agree with the camera's chosen point. That renders the Canon Rebel XT and XTi near useless to me. |
#3
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Focus discrepancies in Rebel XT and XTi, manual and auto focus
BTW, I spent two hours on the phone with various Canon technicians this
afternoon. They seem to think the problem is with my eyes, that I need to adjust the eyepiece diopter. Never a word that this baffling camera behavior is "normal". That's why I'd like to know if other users are getting the same results from the tests. |
#4
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Focus discrepancies in Rebel XT and XTi, manual and auto focus
"Bob G" wrote in message
oups.com... :I have noticed the most puzzling and disturbing focus discrepancies in : both my Rebel XT and my XTi. : : Please do the following tests with yours (and please report back!): : : Set your camera on a tripod : Set up a scene with some sharp black-on-white writing in the center : Set your lens to auto-focus and press the shutter button half way down : until the lens focuses : Adjust your eyepiece dioptric to your eyesight : Shoot a picture at wide aperture (f2.8 will do) : : Now, without disturbing anything, set your lens to manual focus : Move the focusing ring to dislodge the previous focus setting : Re-focus carefully on your viewing screen (do not re-adjust your : diopters!) : Shoot a picture at the same f-stop : : Now upload your pictures to your computer and compare the two : side-by-side by enlarging the center to the maximum (try "actual : pixels" with Photoshop) : : I've repeated these tests with every conceivable variation of lenses, : cameras, with glasses and without, with additional supplementary : diopter correction lenses, etcetera. : : INVARIABLY, the picture done in auto-focus is right on, but the one : done manually shows a pronounced focus shift! You can readily see the : difference in sharpness between the two. : : I sent the XTi to Canon and it was returned with the same problem, : after thorough "inspection and adjusting". : : What is going on? : : Do you see the same discrepancies in your own tests? : Listen to what Rita says here Bob. Your camera is an Auto Focus camera. If you can't get a sharp pic on AF, it has a back focus error. This is not a Professional level camera and you can't expect it to perform like one. If you truly do want to manually focus this camera, get a manual focus screen for it. You may have a problem then with detecting correct AF but it's all a compromise on these cheap SLRs. -- Australian Wedding Photography between Kempsy, NSW and Sunshine Coast. http://www.photosbydouglas.com Digital photos enlarged and printed on Canvas http://canvas.photosbydouglas.com |
#5
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Focus discrepancies in Rebel XT and XTi, manual and auto focus
"Bob G" wrote in message
oups.com... BTW, I spent two hours on the phone with various Canon technicians this afternoon. They seem to think the problem is with my eyes, that I need to adjust the eyepiece diopter. Never a word that this baffling camera behavior is "normal". That's why I'd like to know if other users are getting the same results from the tests. My problem was DEFINITELY fixed with the diopter. Shooting through a viewfinder only, I can never trust my own judgement as to whether I've manually focused correctly or not. I would not be a good subject for your proposed test... dwight |
#6
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Focus discrepancies in Rebel XT and XTi, manual and auto focus
"dwight" wrote in message ... "Bob G" wrote in message oups.com... BTW, I spent two hours on the phone with various Canon technicians this afternoon. They seem to think the problem is with my eyes, that I need to adjust the eyepiece diopter. Never a word that this baffling camera behavior is "normal". That's why I'd like to know if other users are getting the same results from the tests. My problem was DEFINITELY fixed with the diopter. Which brings up a question I've been meaning to ask for some time. How accurate is the built-in diopter adjustment on a low end Canon? I have a Rebel XT and I'm -.5 in one eye and -.75 in the other. And if I start doing more manual focus I will definitely get a Katz Eye, I've been thinking about it for quite some time. Greg |
#7
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Focus discrepancies in Rebel XT and XTi, manual and auto focus
dwight wrote: My problem was DEFINITELY fixed with the diopter. Shooting through a viewfinder only, I can never trust my own judgement as to whether I've manually focused correctly or not. I would not be a good subject for your proposed test... My test removes the possibility of a diopter problem. Notice that in my test the diopter is calibrated after the camera has autofocussed Using manual focus then should give the exact same point of focus, since the eyepiece has been corrected for your eyesight already. |
#8
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Focus discrepancies in Rebel XT and XTi, manual and auto focus
And if I start doing more manual focus I will definitely get a Katz Eye, I've been thinking about it for quite some time. Greg A Katz Eye will not correct an inherent focus discrepancy, should you have one. These are screens whose only virtue is that they're brighter and more contrasty and thereby facilitate focusing, PROVIDED you have a perfectly aligned system to begin with. |
#9
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Focus discrepancies in Rebel XT and XTi, manual and auto focus
On Wed, 17 Jan 2007 18:18:25 -0800, "G.T."
wrote: "dwight" wrote in message ... "Bob G" wrote in message oups.com... BTW, I spent two hours on the phone with various Canon technicians this afternoon. They seem to think the problem is with my eyes, that I need to adjust the eyepiece diopter. Never a word that this baffling camera behavior is "normal". That's why I'd like to know if other users are getting the same results from the tests. My problem was DEFINITELY fixed with the diopter. Which brings up a question I've been meaning to ask for some time. How accurate is the built-in diopter adjustment on a low end Canon? I have a Rebel XT and I'm -.5 in one eye and -.75 in the other. And if I start doing more manual focus I will definitely get a Katz Eye, I've been thinking about it for quite some time. Greg with the camera turned off, can you see the focusing squared clearly? Watch them while you adjust the diopter correction. |
#10
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Focus discrepancies in Rebel XT and XTi, manual and auto focus
"Bob G" wrote in message ups.com... And if I start doing more manual focus I will definitely get a Katz Eye, I've been thinking about it for quite some time. Greg A Katz Eye will not correct an inherent focus discrepancy, should you have one. These are screens whose only virtue is that they're brighter and more contrasty and thereby facilitate focusing, PROVIDED you have a perfectly aligned system to begin with. Yes, but as others have pointed out the lack of a decent focusing screen on current autofocus DSLRs is probably your problem with manual focus, not an inherent problem with your Rebels. Greg |
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