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Old Apr 30, 2008, 9:28 PM   #1
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I've read numerous reviews and posts regarding "Brand X" lens and how they didn't get good one. Some were RMA'd and some were sent to the manufacturer for "calibration". Other than taking a bunch of pics and looking at the results for "softness at the extreme ranges, focus speed problems, etc, is there any easy, quantitative way to measure if your new lens is not quite up to spec? If one buys a new lens, what are the things to do to check if it is a keeper or dud?
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Old May 1, 2008, 9:50 AM   #2
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There is no way to know whether a lens is bad or not before buying it. You just have to use it. Some lenses have greater sample variety from lens to lens....I've seen more issues with 3rd party lenses than with the big boys (Canon and Nikon). Some of the focus issues may even be related to issues with the camera body. There are many standard tests you can do to test for back focus or front focus, just google these terms to find one you can do. Most zoom lenses are going to have some distortion issues. Many can be corrected via software...PTLens, DXO are expamples of software correction tools.

I'm also convinced that these issues are not all lens related. Higher resolution cameras a less tolerant to bad technique. Sharper resolution maginfies things like camera shake, or other poor technique issues that can create less than tack sharp images.
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Old May 1, 2008, 9:45 PM   #3
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Natty wrote:
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Some were RMA'd and some were sent to the manufacturer for "calibration".
The term is not calibration but rather collimation. This means, for camera lenses that each optical element of the lens is centered on and perpendicular to the optical axis.
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Old May 2, 2008, 6:30 PM   #4
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rj and ac.....Thanks for the info. I'm almost certain that in my case, technique, rather lack thereof, will be the cause of most of my problems but I'm working on that. So is it fairly routine forany of the lens manufacturersto take in lenses for collimation? Does a lens go out of spec from usage (assuming of course it hasn't suffered any sort of trauma or missuse)?



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Old May 2, 2008, 9:01 PM   #5
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Natty wrote:
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So is it fairly routine forany of the lens manufacturersto take in lenses for collimation?... Does a lens go out of spec from usage (assuming of course it hasn't suffered any sort of trauma or missuse)?



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No it's not fairly routine, most lenses deliver pretty close totheir capabilities.

Eventual wear in the focusing mount can cause the focus plane to tilt with respect to plane of the sensor. Diaphrams can move inaccurately due wear or more commonly lubricant leaking from the focusing mount. This is not an all enclusive list but typically the optical elements don't de-alignment without trama.
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Old May 2, 2008, 9:44 PM   #6
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ac.smith wrote:
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Eventual wear in the focusing mount can cause the focus plane to tilt with respect to plane of the sensor.
So that's why a metal mounting ring is preferred over composite (i.e. plastic). I didn't realize that years of use could cause the mounting ring to wear to a point where the plane would no longer be true. Make perfectly good sense though now.

And I thought the composite was a nice to have to save on weight. :?
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Old May 3, 2008, 5:03 AM   #7
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There are also 2 factors that hugely magnify the apparent problem:
  1. When an experienced photographer pays a lot of money for a lens and its performance is sub-par they complain loudly in the forums. When the lens performs well they are silent. So you get a false impression of how common the problems are.[/*]
  2. Novices who are unable to get good pictures (even with expensive equipment) are prone to believing that they have the same problem as the pros report, when in fact they simply don't know how to use the equipment properly. So they complain loudly and take the lens back, but since the problem was never with the lens in the first place they get a new lens with the same "problem" - i.e. the user. So they take it back again, and again. Eventually one of three things happen:[/*]
    1. They randomly take some shots that look better than their previous efforts and declare themselves happy that they have a good copy.[/*]
    2. They finally figure out what it is they have been doing wrong all this time and declare themselves happy they have a good copy.[/*]
    3. They loudly proclaim themselves disgusted with the brand and switch from Nikon to Canon or vice versa. And without testing too much (they are beginning to catch on that it might be their own fault) declare themselves happy.[/*]
At this point the novice will then make pronouncements about how bad the quality control of their out-of-favour manufacturer is and go on to say they had to try 5 copies of the lens before they got a good one.

How can you tell whether they know whether to give their account any credence or not? Well the best thing you can do is check out their websites or Flickr stream. If their photos are mostly of test charts, their pets, and poorly composed and exposed shots of scenes of natural beauty then you can pretty much ignore what they say.

Before you get too caught up in obsessing about equipment, check out sites like http://www.oneexposure.net and see how many really good photos you can find from people using very "ordinary" DSLRs and lenses.

I don't subscribe to the "equipment doesn't matter ethos", it does matter and you should get the best you can afford, or alternatively if money is no real object then just get what you like. But for "normal" photography any of the current DSLRs and standard zooms are very close in their capabilities and the photographer will be far more of a limiting factor than the eqiupment.
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Old May 3, 2008, 2:41 PM   #8
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peripatetic......what you've said make perfectly good sense. In searching reviews of various lenses Iran across posts which proclaimed they "finally got a good one", or something like that. I read so many reviews lamentingQC issues and buyers returning the same lens multiple times, or switching to a different model or brand, that I was somewhat surprised. I sort of took it for granted that modern production methods of the "big" name brands would be such that there should be very little, if any variance between same units produced so reading those posts certainly made me suspicious.

I harbor no illusions that my equipment is the limiting factor in my photographs. I know full well that I have a VERY long way to go in learning how to properly and best make use of what I have. Honestly, it is a ball of fun learning.

As is so often the case, the same equipment in skilled hands can produce amazing results. I'm an avid fly-fishermen and what I've seen in thatsport is very much as you state.....well meaning and eagerpeople constantly purchasing more and "better" equipment and inalmost all cases, much more expensive equipment, only to find out that it wasn't the first 3 rod/reel combinations that their casts to ball up in a mess of fly-line and leader only a 10 feet from their feet.

Using the fly-fishing example, or any countless others like it, I've resigned myslef to keep thingssimple and inexpensive (as much as possible where this stuff is concerned)until I can skillfully make use of what I already own.



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Old May 3, 2008, 3:23 PM   #9
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Natty wrote:
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And I thought the composite was a nice to have to save on weight. :?
Don't discount composite materials.

First, theyhave a lower coefficient of friction that metals, and so are more likely to tolerate significant wear.

Second, they are more elastic and have a lower coefficient of thermal expansion than metal, so they are more likely to tolerate multiple changes in temperature. When a metal lens mount warms, it will expand more than a composite mount, and so optical elements are more likely to become misaligned, and when it cools, it is more likely to become permanently deformed as it tries to shrink around optical elements that aren't contracting as much.
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Old May 3, 2008, 3:38 PM   #10
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Geez...there are so many things to consider! I don't know if I'm coming or going anymore :?.
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