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Old Oct 20, 2008, 4:23 PM   #21
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Boldstar wrote:
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Maybe I don't completely understand what that means. This is a combination of apature and the lens capability, right? And my apature-priority F numbers go up pretty high... higher than my S2 if I remember correctly. Shouldn't a high F-number bring everything into focus?

DOF is controlled by several factors:

1. Sensor Size

2. PHYSICAL (not 35mm equivelent but actual physical) focal length of the lens

3. Aperture

4. Distance to subject

So even if 3 and 4 are the same between the S2 and a DSLR, you have to account for 1 & 2. Because the physical sensor and physical focal length of the lens on the S2 is smaller you get deeper DOF (if the values for 3 & 4 are the same for both cameras).


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Old Nov 4, 2008, 1:38 AM   #22
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I've posted a very long note on another thread above about XSi Autofocus problems, but i would like to comment about this initial post.

I think we all know, or can easily learn how those key 4 factors affect DOF but on this specific case look at the lenses he is using,.. 1.4 has got to be one of the top lenses. My point is that people could expect a low cost lense like the 18-55 AF/IS KIT lense to produce out of focus shots, his shot of the baby is a great example of Front Focus. I will go back and look at the hand or the toy at 100% but I bet it will be great. So the Camera is at fault. He bought his in July, I got my in October,... Canon must be selling a 1000 of these a month.

This baby shot is way out of focus. If we had his image it would show the focus point. He said he was focused on the eye, but the size of the focus SQUARE or Spot is much larger than the "RED" led in the view finder. But even with that the focus point has got to be 3-4" in front of the eyes.

Memento,... what are your plans to get your camera fixed? Mine is no where near as bad as your FF but I'm sending mine to Canon for adjustment. My problem is sometimes it does focus and sometimes it does not. It all depends on the Contrast of the item I'm trying to focus on. If I focus on black lines on white paper in good sunlight,...it is perfect. If I try it on a flower that is of one monolithic color, it can't get good focus.
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Old Nov 4, 2008, 4:48 AM   #23
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jbird1938 wrote:
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I think we all know, or can easily learn how those key 4 factors affect DOF
Actually, Boldstar asked a question and I answered it. But thanks for speaking for evryone else on the thread :blah:
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Old Nov 4, 2008, 7:34 AM   #24
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jbird1938 wrote:
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I've posted a very long note on another thread above about XSi Autofocus problems, but i would like to comment about this initial post.

I think we all know, or can easily learn how those key 4 factors affect DOF but on this specific case look at the lenses he is using,.. 1.4 has got to be one of the top lenses. My point is that people could expect a low cost lense like the 18-55 AF/IS KIT lense to produce out of focus shots, his shot of the baby is a great example of Front Focus. I will go back and look at the hand or the toy at 100% but I bet it will be great. So the Camera is at fault. He bought his in July, I got my in October,... Canon must be selling a 1000 of these a month.

This baby shot is way out of focus. If we had his image it would show the focus point. He said he was focused on the eye, but the size of the focus SQUARE or Spot is much larger than the "RED" led in the view finder. But even with that the focus point has got to be 3-4" in front of the eyes.

Memento,... what are your plans to get your camera fixed? Mine is no where near as bad as your FF but I'm sending mine to Canon for adjustment. My problem is sometimes it does focus and sometimes it does not. It all depends on the Contrast of the item I'm trying to focus on. If I focus on black lines on white paper in good sunlight,...it is perfect. If I try it on a flower that is of one monolithic color, it can't get good focus.
You seem to be a bit mixed up.

The 50 1.4 is a decent lens, but hardly "top" of anything.

The camera body does the focus, not the lens. A slow AF motor can make the camera hunt a bit more. A slow lens lets in less light, so can degrade AF performance.

You want pro-grade AF in a cheap body. Well we all want more for our money, but you seem to be taking it rather personally that your expectations don't match the reality of what you can get for the price you have paid.

AF systems work on contrast. Try to focus on a white wall with no texture. It's basically impossible. Actually - try it manually. It's almost impossible to do it by eye too.

Send your camera back for calibration by all means, but you should also realise that all equipment has its limits, and learning to work within those limits rather than railing against them is often more productive for your output and better for your blood pressure.

Of course if your equipment is not working properly then get it repaired, but once it's within spec either learn to get the best out of it or face up to the fact that your requirements are going to cost you. No use getting mad at Canon.


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Old Nov 4, 2008, 9:35 AM   #25
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I know I haven't posted in a while, but I've been following the discussion. Thank you JohnG for elaborating on the DOF stuff.

I've been taking lots of pictures over the past couple of weeks, fall colours and all that, and I've had some mixed results. Some shotsare great, some shots are crap (in focus andout of focus, respectively). But I've learned quite a bit from the "For Dummies" book I bought and things are definitely improving.

That being said, I completely disagree with the notion that the XSi should produce anything but perfectly-focused pictures. While I realize that it's an entry-level DSLR, and "you get what you pay for" and all that jazz... it shouldn't bethat difficult to get in-focus pictures with a thousand-dollar camera. If a point-and-shootcan capture better photos than your DSLR (after you've learned the basics), then there might be a problem.

If a camera can't focus, it's useless. In fact, I'd like to assume that getting your camera to focus properly should be a minimal expectation. There are lots of other things to worry about when taking/composing a shot... I'd like to think that my camera could look after that one detail for me.

I'm certainly not taking the viewpoint that the camera is at fault here. Like I said, I'm getting some better results now. But I have to wonder if there might be some truth to the issue. I mean, are there forum discussionthreads popping up all over the Net talking about Nikon D80 focus issues? (I threw that model into the discussion because it was my second choice.)

I'd love to have the opportunity to shoot the same subject with a few different DSLRs, all with similar lenses and identical settings, and then compare the results.

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Old Nov 4, 2008, 10:00 AM   #26
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I went through the focus test a few times and my camera does front focus, but not exclusively. It is not far off. The problem lies in using the extreme shallow DOF. That is just too narrow. If I limit it to f/2.2 and above, the issue pretty much disappears. The lens is still a great looking lens that takes great pictures. So I'm doing a few things. Increase the f-stop, increase the ISO, and use a flash. Here's a picture that I took at ISO 400, 1/50 shutter, f2.2, no flash.



And this one is ISO 100, f/2.8, 1/200 shutter, speedlight 430ex flash with Gary Fong Lightsphere (the BEST flash accessory ever).



Canon tech support does not have focus specs. At least that's what they tell me. So I have nothing to compare my test it to. As far as I'm concerned, the focus test shows that the focus tolerance is the problem and that is something that most likely cannot be fixed with my camera model. Even though it's a $700 body, it's still not a pro camera. I could easily just use f5 to eliminate all focus concerns and it will still be better than any point-and-shoot. So I think what I'm seeing is the limits of my camera and I've adjusted my technique to compensate.

I should add that I did the focus test with my original digital rebel (300D) and had nearly identical results.
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Old Nov 4, 2008, 10:09 AM   #27
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memento wrote:
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I went through the focus test a few times and my camera does front focus, but not exclusively. It is not far off. The problem lies in using the extreme shallow DOF.
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I should add that I did the focus test with my original digital rebel (300D) and had nearly identical results.
OK, that last test is very beneficial. What it tells you is the front-focus isn't a CAMERA issue but likely a lens issue. You have the option of sending the lens and camera in to canon for calibration as has been suggested several times. This type of situation is probably not that uncommon. It's one of the things that sets pro-grade lenses apart from consumer grade (i.e. less tolerances for front/back focus).
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Old Nov 4, 2008, 10:42 AM   #28
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JohnG wrote:
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memento wrote:
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I went through the focus test a few times and my camera does front focus, but not exclusively. It is not far off. The problem lies in using the extreme shallow DOF.
Quote:
I should add that I did the focus test with my original digital rebel (300D) and had nearly identical results.
OK, that last test is very beneficial. What it tells you is the front-focus isn't a CAMERA issue but likely a lens issue. You have the option of sending the lens and camera in to canon for calibration as has been suggested several times. This type of situation is probably not that uncommon. It's one of the things that sets pro-grade lenses apart from consumer grade (i.e. less tolerances for front/back focus).
shoot. I should have mentioned that this is not exclusive to the 50mm lens. My tamron 17-70mm focus wanders from front to back and my other canon lenses, 50mm f1.8 and 28-135mm IS are slightly front focused as well. This applies to both cameras. It's consistent and with the changes to my technique, I don't plan on sending anything back to Canon.
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Old Nov 4, 2008, 11:19 AM   #29
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memento wrote:
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shoot. I should have mentioned that this is not exclusive to the 50mm lens. My tamron 17-70mm focus wanders from front to back and my other canon lenses, 50mm f1.8 and 28-135mm IS are slightly front focused as well. This applies to both cameras. It's consistent and with the changes to my technique, I don't plan on sending anything back to Canon.
Out of curiosity, just wondering if what you see is actual front-focus vs. the fact that an image typically has more in-focus in front of the focal plane than behind. For instance if you were shooting a ruler (typical focus test) - yes you want to see the point you're focusing at in-focus but you should NOT see an equal amount of distance behind the focal plane and in front of the focal plane in focus. The fact you're describing the same affect with 4 different lenses across 2 different bodies makes me wonder. You also mentioned you changed your technique and thus are not going to send in your gear. Does that mean that your change in technique has resulted in more consistent focus?
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Old Nov 4, 2008, 11:31 AM   #30
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Boldstar wrote:
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That being said, I completely disagree with the notion that the XSi should produce anything but perfectly-focused pictures. While I realize that it's an entry-level DSLR, and "you get what you pay for" and all that jazz... it shouldn't bethat difficult to get in-focus pictures with a thousand-dollar camera. If a point-and-shootcan capture better photos than your DSLR (after you've learned the basics), then there might be a problem.


Boldstar - I can't say if your camera has a problem or not - it very well might. However, look at it this way - a digicam doesn't focus better in most cases it simply has a much, much greater depth-of-field. So mis-focusses aren't as noticable.

I have professional gear - some of the best on the marketand I still get out of focus shots. About 1% of those shots are the gear's fault.

I liken this situation to a person used to automatic transmissions learning to drive stick shift. Gosh, the car should perform at least as well as the automatic shouldn't it? Yes, it should, once you learn how to use it. There is technique involved - just like with focusing. At first you have to pay attention to that technique (i.e. with a camera - you have to ditch the point-and-shoot mentality). After a time it becomes second nature. A DSLR is a better tool, but that doesn't mean it's necessarily as easy to use. Just like manual transmissions provide better performance, so to do AF systems in DSLRs - once you know the techniques for using them.

As an example - when I hand my DSLR off to a family member to take a photo I get a LOT more OOF shots than with a digicam. But not surprisingly a lot more OOF shots then when I use the gear. It doesn't mean the gear is defective - just that they don't know how to focus accurately with it. So with them, they're relying on chance to get the shot in focus. I rely on technique.

Again I can't say your camera is or isn't defective. But I can say an expectation that it behave like a point and shoot and have the same depth-of-field is NOT a realistic expectation.

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