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05-19-2010, 09:15 AM   #16
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Lens testing is a very tough issue. I have done many in order to try and verify the quality of my lenses, and compare one lens to another. I have found it very difficult to decide exactly how to do them. I do think that for comparing lenses to each other a tripod and 3 sec mirror lock are required. For example I try to test inside at night with artificial light so that there is little variation in the light from lens to lens. However, I do think it's important to test the lens in conditions most like you will use them. I remember conducting comparisons of 200 and 300 mm lenses with the tripod at 6 feet from my subject because the room was small, and then asking myself later, when am I going to use these lenses at 6 feet? What if they perform differently at 60 feet, a distance I'm more likely to use them at?

A main question also is, what is the purpose of performing the test? I think most people perform tests for their own purposes and then post the results here because they think other people might be interested. In those cases, the tester may not be concerned about CA or distortion. I know for me, I'm usually looking for sharpness and detail rendering because that's what appeals to me vs. some people value returning how the lens handles colors much more. If the purpose of the test though is to try and prove something to others, then more care needs to be taken.

I know one thing I would like to see in people's lens tests are subjects with fine texture, so that sharpness can be seen easier. Subjects that are side lit help this. Also, for me, since I most often shoot .jpg, that's what I do my tests with. Taking RAW is certainly more "pure", but not as relevent to me for my own tests.

Even being as careful as I try to be, I have seen significant differences between shots with the same lens with the same settings at times. I suspect the most likely culprit is camera shake. It can get frustrating.

I appreciate any information that people post here to share. Some people have more time and take much more care, and others just post some quick results. Based on what they post, I figure out what I think I can learn from it.

05-19-2010, 09:15 AM   #17
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For me a survey of real world examples show the best a lens can do, and in which situations.
05-19-2010, 09:17 AM   #18
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QuoteOriginally posted by pcarfan Quote
These would be useful in 'user reviews' after getting familiar with the lens. So, the image posted just shows what is possible.

But, I think one image as a 'test' would'nt be useful in gauging how good a lens is, as it would be full of varying parameters that it would be virtually impossible to compare to another lens.
If I'm looking at a lens and looking for user opinions before I buy, I'm more interested in what is possible with the lens (or any other piece of equipment). I look through the lens database here and at some of the reviews that people post. It always amazes me (probably shouldn't) that some one complains in the cons section (for example) that a M135 f3.5 doesn't focus close enough or is an M lens or isn't f2.5 or some other silly statement. They then go on to describe what is wrong with Their copy as if to state that it's a problem across the board. They then give the lens a low rating, and in the case of Their copy, it may be deserved, resulting in an overall junk rating for the lens.

Show me some pictures you took with the lens, tell me what you did to enhance them (if anything), and tell me what camera you used to take the photos. I don't give a damn about resolution charts, photos of brick walls, etc, all I'm interested in at the end of the day is what *I* may achieve with the lens.

That, of course, is just my opinion. I know you and others will disagree but I'm not running around taking pictures of brick walls and resolution charts. Watching someone else do it is completely pointless to me.

05-19-2010, 09:23 AM   #19
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In addition to the reviews on this forum, how do you feel about the lens tests over at Pentax Lens Tests at photozone.de? Are there other sites that give a detailed objective view besides photozone?

05-19-2010, 09:49 AM   #20
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QuoteOriginally posted by Edmund Quote
In addition to the reviews on this forum, how do you feel about the lens tests over at Pentax Lens Tests at photozone.de? Are there other sites that give a detailed objective view besides photozone?

This is my opinion.

Before I purchase a lens I check as many tests as I can. Photozone is one of the primary sites I use. But, I am open to any site (SLR lens review ?, Photodo and even DPR). But, I never totally rely on them.

Then I take a look at the reviews posted here (Fred Miranda, MF lens forum) etc. and give more weight to those.

I do a google search and read what ever I can read about the lens.

Then I look at hundards and hundrads of photos posted in Pixelpeeper.com, flickr and Pbase. My final decision is based on this. Also, I use the 'post your photo' section here and other sites.

Is photozone helpful, YES....but do I beleive Photozone tests reveal everything needed to evaluate a lens like say the FA limiteds ?, hell no!....not even with the stuff they measure, like the sharpness. The FA43 is much sharper at f1.9 than the test reveal, and I am certain the DA*55/1.4 is much better at f1.4 than photozone says it is, just to point out a few......so, if you read photozone and didn't buy the FA43 for it's softness wideopen, you'll be missing out on one of the best Pentax lenses ever made.

But, when I do a google serach and get a hit of any amature 'tests' done it has always been helpful for me. So, I wondered whether it help others as well.

Last edited by pcarfan; 05-19-2010 at 10:01 AM.
05-19-2010, 10:03 AM   #21
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QuoteOriginally posted by pcarfan Quote
This is my opinion.

Before I purchase a lens I check as many tests as I can. Photozone is one of the primary sites I use. But, I am open to any site (SLR lens review ?, Photodo and even DPR). But, I never totally rely on them.

Then I take a look at the reviews posted here (Fred Miranda, MF lens forum) etc. and give more weight to those.

I do a google search and read what ever I can read about the lens.

Then I look at hundards and hundrads of photos posted in Picelpeeper.com, flickr and Pbase. My final decision is based on this. Also, I use the 'post your photo' section here and other sites.

Is photozone helpful, YES....but do I beleive the photozone tests reveal everything needed to evaluate a lens like say the FA limiteds ?, hell no!....not even with the stuff they measure, like the sharpness. The FA43 is much sharper at f1.9 than the test reveal, and I am certain the DA*55/1.4 is much better at f1.4 than photozone says it is......

But, when I do a google serach and get a hit of any amature 'tests' done it has always been helpful for me. So, I wondered whether it help others as well.
Thanks. I have just started doing some of the steps you mentioned, especially trying to find various tests, opinions, and samples of a lens' output. I just entered this DSLR world during Christmas when I purchased the K-7. Now I am trying to upgrade my lens inventory. While photozone is good, I have found it not being quite consistent with other opinions/evaluations. I will keep searching and reading...
05-19-2010, 11:01 AM   #22
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This is where the club threads are really helpful. They encourage a broad range of users to post photos taken with a limited range of lenses. Interestingly, the clubs seem to contain a fair number of photos that show the weak points as well as the strengths.

As for my personal approach, I prefer to use a standard set of real world subjects. People who have read my reviews are probably familiar with my daughter's china doll, the pewter box, my watch face, etc.. The intent is to provide a set of challenges for the more common areas of interest/concern. These would include:
  • Center sharpness wide open, f/5.6, and f/11
  • Edge sharpness wide open, f/5.6, and f/11
  • Contrast
  • Near bokeh wide open
  • Far bokeh wide open
  • Far bokeh at moderate apertures (many lenses are extremely week here)
  • Resistance to CA (lateral and longitudinal)
  • Color cast
  • Color rendition
  • Resistance to flare
  • Tendency to PF (not always the same as CA)
Beyond optical characteristics, I also like to address practical issues of build and usability and physical appearance (ugly lens anyone?). And, in the end, there is the intended use. Case in point might be my Jupiter-9. It is heavy and cumbersome to use and distinctly soft with low contrast wide open, but it truly shines for some subjects due to its color rendition and pleasing bokeh at all apertures. Another example might be the Pentax-DA 10-17 Fisheye. It has a terrible tendency to PF, but is also an extremely useful and fun lens and much-loved by its owners.


Steve
05-19-2010, 11:43 AM   #23
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Interesting discussion so far. Like some posters I'm not a terribly big fan of brick walls at x f and 1/xxx. I prefer lens reviews to lens tests. Another thing I look for is consistancy in the reviews. If I read one "The Zenitar 16mm Fisheye is garbage wide open" that is one thing. However if I read many saying "The Zenitar 16mm is very soft at F2.8" that is a different thing entirely. My lens buying decisions are also based to a large degree on hear-say evidence. The first lens I ever bought (outside of the 18-55 kit that came with my DS) was the FA 50mm F1.4 because so many had sung it's praises over at DPR (before this site even exsisted) and I liked the shots I saw taken with it. That type of information is much more relevant to me that any report posted at photozone or where ever. I also pay more attention to what some people say because I admire their work more, or because I realize that their shooting philosphy is closer to mine.

NaCl(I guess what I'm saying is that I prefer personal/human reactions than numbers)H2O

05-19-2010, 12:14 PM   #24
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I do strongly prefer user reviews and tests and usually skip any lens testing in magazines, as I have seen too many examples, where certain lenses where denoted, just for marketing purposes.

But there are some basic requirements, which are often violated, when the average user performs a test, namely the choice of subject (detailed, minimum contrast, fixed, no movements withing the subject, no variable lighting etc.) Therefor, the good old brickwall has some advantages.

So my personal prerequisites, to make a test meaningful:
  1. forget about absolute numbers, not home made resolution numbers or MTF curves, as I find the complexity to make such a measurement in a meaningful and repeatable way is too high and would afford too much time
  2. it is always helpful to make lens comparissons, instead of just showing the performance of one single lens
  3. the subject should not be a test chart placed near the minimum focusing distance! This is an approach I see too often, but it is totally useless, unless testing a macro lens. At near distances, nearly all lenses (apart from said macros) perform worse than under standard conditions. Also lens aberrations will be much more pronounced in their effect (field curvatore is disastrous at near distances) and lead to conclusions, which are simply not valid for real world use, because you can only have the center OR the corners perfectly focused!
  4. Another problem when shooting at short distances is, to get the camera really parallel to any testing target. Otherwise one side of the image could be slightly out of focus and the reviewer assumes bad centering of the lens…
    This is really not a simple task. At farther distances the increasing depth of field will counter the unavoidable user error.
  5. tests should be done at distances at least twenty times the focal length, better at more relevant "typical" shooting distances and as such must vary according to the focal length.
  6. artificial lighting will not only influence AF sometimes and white balance, but influences contrast and that can lead to wrong conclusions. So natural daylight, with no harsh sun light or shadows would be much better
  7. changing light during a test session is bad. Any image taken in brillant sunshine will look "sharper" and more contrasty, as the same scene under cloudy sky. SO if lighting changes fast, lens testing gets really difficult.
  8. with really long lenses, one is tempted to choose a test target a couple of hundred meters away. That is only possible on a cold winter day with a totally calm atmosphere. On any other day, the local turbulences (especially, when there are streets, buildings and other artificial structures between the lens and the target will severly degrade the IQ
  9. Obviously all negative effects should be reduced: heavy tripod, solid tripod head, mirror-up, remote trigger, all camera settings on neutral,
  10. the test target should have a good mix of colours, some sharp, well-defined edges and some areas with hight contrast edges (CAs!) and lots of fine but good to discern detail. I have seen sample shots of foliage, but I think, that the detail in foliage is hard to discern and changes from image to image (due to wind), which makes any conclusion doubtful

There are sure even more things to consider, but that is basically, where I see problems, which should be adressed in the test set-up.

Ben

Last edited by Ben_Edict; 05-19-2010 at 02:21 PM.
05-19-2010, 12:21 PM   #25
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Ben, good assessment.
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