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Old Jan 24, 2005, 7:41 PM   #21
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Well, getting back to the first post I made in this topic 90% of the pictures I take with my zoom lenses I manually focus. This is because I don't trust the lens to pick out the item in the picture that I want to be in focus. This usually happens when I photo a deer or bird in fairly thick brush. When auto focusing there are too many layers for the lens to choose and usually it picks the wrong item. Now if I us the 70-200 with either the 2x or 1.4x tc the non auto focus function won't bother me. So will one or the other of the TC's be sharper?

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Old Jan 25, 2005, 2:36 AM   #22
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I have the 2x used with my 70-200IS. The 1.4 must be sharper because it spreads the light less. So whether you want reach or sharpness should drive your decision. If you want both, you need to buy reach by getting that nifty 400mm DO lens.


ps: Swapping lenses was how I "discovered" I had a problem. A buddy wanted to try my expensive lens before buying. We compared images taken seconds apart on his D10 against his 70-300. The 70-300 was sharper than my 70-200L. I was appalled. So I took my 1Dmk2 and 70-200 back to the camera store and tried another 70-200. Sure 'nuff, the other 70-200L focused where it should.

I guess the point is both the camera and the lens can be out. Shipping and handling can affect cal. So the best way to go is to have the entire system cal'd together. And yes, I do have multiple bodies. And the focus problem was primarily with that lens.



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Old Jan 25, 2005, 10:19 AM   #23
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Guys don't get me wrong - I'm not saying a lens can not be faulty! :-)

When you have multiple bodies like me, it's pretty easy to determine which lens is bad (and you don't need a friend for this) because it doesn't focus well with any of the cameras

The issue arises when a lens focus 'good' with one body and not the other, which 'system' need to be calibrated?
You don't want to be adjusting a lens to the wrong 'system' - affecting your future (or past) purchases :idea:
... of course with 1 body it's kind of hard to determine (even though it might work with some lenses)
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Old Jan 25, 2005, 10:46 AM   #24
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Last week the weather was nice and I took my Canon 70x200 IS with 1.4 tele to the pond to see what I could get. I came from a standard film camera and am amazed at the differenc in focuse speed. The Canon is just in anothe field for me. I wam attempting to get birds in flight so have been useing auto focus instead on manual. I'm kinda slow in manual mode. Camera/lense was able to keep up with many incoming birds at short ranges [which is where it really has to work].

The lense is 2.8 which gives me much better low light use or allows use of a tele. extender and still keeps me around the F4 mode. This allows better indoor or low light field use. Seems like the light is always right for me.

If it is affordable for you, consider this lense. From what I have read, don't be afraid to use the Sigma 70x200 or the Canon F4 as these are very good lenses also.

In summry; I suggest the Canon 2.8 70x200 IS if you will be shooting indoors or in low light, otherwise, the other lenses should serve you well also.
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Old Jan 25, 2005, 12:55 PM   #25
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All else equal, the lens without the TC is going to be better than the lens with a TC. Furthermore, a TC with less magnification is going to be better (sharper, brighter, less distortion) than a TC with greater magnification, all else equal.

Inthis view, the Canon 1.4x TC is regarded as better than theCanon 2x TC. A 400 f/5.6 L is better than a 300 f/4 L + 1.4 TC. (Says Reichmann.)

The manual focus issue with a TC is not just about losing autofocus, it's also about losing light in the viewfinder. A f/8 lens may still be usable, but probably only in bright light -- it will sometimes be too dark to focus well otherwise; that f/8 aperture will also require you to drop the shutter speed in order to compensate for the light loss; this may make the images too blurry due to motion (cameraand subject). DSLR's have the advantage of being able to boost the ISO -- this will likely be a good technique for overcoming the shutter speed loss; post-processing noise reduction may be needed.

I got a Canon 1.4x TC myself instead of a 2x. These TC's are not inexpensive; I decided to spend it on the better one. Optical quality is a matter of personal tastes / goals, and going down in quality is a direction that I like to avoid whenever possible. So the 1.4x makes sense for me; the 2x does not.
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Old Jan 25, 2005, 4:33 PM   #26
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Well, I finally got the second Canon 70-200 f/4L from B&H. This one does seem to focus well with my 20D except for one little problem that is very bothersome to me.

It seems that it takes very soft images at f/5.6! I set the camera up on a tripod and took some shots of an easily focused on target in my office. I used the timer. At the different f-stops to either side of f/5.6 the focus looked great viewed at 100%. But, at f/5.6 the image was so much more visually softer than the images at the other f-stops that I'm wondering if I should yet again return this lens. I've heard of lenses having "sweet" spots, but is it possible for a lens to be good all-around but have a "sour" spot?

What would you do? Any suggestions for how I can further test this or determine what is going on here?
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Old Jan 25, 2005, 11:49 PM   #27
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I'd check the focusing technique first. It's very easy to get the focus off by a bit, esp at the wide apertures, and to think that a lens is soft because of that.

There's a focusing test that can be used -- essentially place a ruler along your direction of shooting. Some point should be most in focus; you can watch that point move as an area perhaps better than to identify the exact point. I.e. focus in and out -- you should see the entire set of lines with blur on both sides; the center of that region is the point most in focus. You might not be able to see that point, but be able to judge it based on the rest of the area; particularly when it moves.

I found in detailed examination using a 20D in capture mode that my best focusing was done when I used a combination of my eye together with the focus indicator in the camera.

The standards of quality for auto-focus is that the selected focus area must be within the depth of field area (for some unclear parameters). Essentially, Canon does not promise that they will get auto-focus exactly right; only roughly right. On pro lenses (f/2.8 or faster), with HP sensors (20D and above), they do promise tighter tolerance for focusing (in decent light), but still not perfect. Theycan't really, and maintain price and focusing speed. It's a trade-off.
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Old Jan 26, 2005, 6:06 AM   #28
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geoffs

You really have to test it in 'real-life' situations like the low-contrast shots you were having before with your otherlens - High contrastfixtest charts(where most lens tests are performed) are easy target as the lens always get it right especially in good lighting: It's the 'real-life' condition on how you use the lens that really count!

Madwan is also correct the 20D's high precision AF sensors only kick in with lenses with aperture of f/2.8 or higher -At f/4 theses high precision sensors are not enable especially up close (ie indoor) where the DOF is @ their shallowest!
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Old Jan 26, 2005, 10:52 AM   #29
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I am aware of the points, NHL and madwand, that the both of you have made. It's all good advice that everyone should be aware of. I do really have to put the lens through a much more comprehensive "real-life" set of situations as well as the good old ruler test for focusing.

However, I did think it strange that in my simple test, that under exactly the same conditions f/4, f/4.5, f/5.0 would yield very nicely focused results while f/5.6 results were obviously OOF. And then on the other side of f/5.6 things would be nicely in focus again...
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Old Jan 26, 2005, 11:13 AM   #30
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What is the website for Bob Atkins paage on testing for focus. I just orderd a Canon 70-200mm f4 L lens and am expecting it in two days.
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