"This lens is soft" and other facts

<p>Have you read this article? The author claims that variation in camera lens and bodies happens more than you might think and that it isn't always random. Here's a quote:</p>

 

<blockquote>

<p>I’m going to conclude that some lenses have intrinsic problems that make them bad even when properly focused (yeah, I know you already know that). I’m also going to conclude that some cameras bodies have intrinsic problems that make many lenses bad <em>on that body</em> despite accurate autofocus (yeah, a few of you knew that, too). Then I’ll talk about what kind of things can cause those problems and speculate at length about “bad batches”, “bad cameras” and what it all means for the photographers, gearheads, and pixel-peepers among us (yes, those are three different, if somewhat overlapping, groups).<br>

http://www.lensrentals.com/news/2010.03.06/this-lens-is-soft-and-other-facts</p>

 

</blockquote>

<p>If he's right, it would probably be prudent to test your new camera and lenses as soon as you get them. The thing is, he doesn't go into much detail as far as the testing. How would you go about testing your gear?</p>

<p>

<p>I have had any number of lenses that has problems, and ended up going back. I have seen two problems with some of the lenses I have bought, one is where one side of the image is nice and sharp and the other side is way soft. I have also had lenses that had a very hard time auto focusing. In both cases I have tested the lenses on two different bodies and both camera bodies showed the same problems with the lenses.</p>

<p>This is one of my test shots showing a problem, the upper left corner of the image is way soft while the lower right is fairly sharp, this was true with just about all the shots using this lens. Clearly something was out of wack, we sent it back and got another which worked just fine.</p>

</p>

<p>Hmm, how do you know there is a problem with a lens or camera body in the first place though? Is photographing newsprint or a brick wall enough to tell?</p>

<p>You might want to take a look at this - http://www.bobatkins.com/photography/technical/testing_lenses.html</p>

<p>It's something I wrote a while ago about testing lenses to make sure "you got a good one".</p>

<p>Bad lenses are very much the exception rather than the rule, and I suspect that many reports of bad lenses are due to user error. However defective lenses certainly do exist and it probably pays to do some sort of testing just to make sure there are no obvious problems</p>

<p>Thanks, Bob. I had not thought to check for defects such as bubbles. Checking and exchanging kit lenses seems like it would be trickier since you would probably have to exchange the entire kit.</p>

<p>Also, is focus hunting a sign of a defective lens? I'm considering the Olympus 70-300mm which is known to have some issues with hunting, though it is otherwise considered to be a good lens.</p>

<p>I see I forgot the link to my test photos, I will try again<br>

<a href="

<p>This clearly shows a much sharper image in the upper left corner then the lower right.<br>

Using the camera camera with a different len of the same focal length did not show this problem, it is was not the camera. And as I said a new lens fixed the problem.</p>

<p>Though, I do come across defective lenses very rarely but Scott, thats a very strong variation. even if it is defective i assume i see symmetry in all directions as the lens is spherical. We use so many lenses in our labs. I have never seen such variations.<br>

It looks the lens is tested at maximum aperture. Is there a possibility that the paper which is focused is not perfectly flat or inclinded which manifests in such varation. probably, the other lens is tested at same focal length but with different aperture settings....just my guess..</p>

<p>Things certainly do slip through quality control on occasion, but I think Bob is absolutely right, that this is not common, at least with the major manufacturers. Cheap lenses from East Photokistan, maybe more often.</p>

<p>I've generally stuck with top notch lensmakers and only had softtness problems with one of their lenses in over 40 years. The testing process I use is pretty simple, and I generally have an excellent lens on hand or a my disposal to compare the new one with. I test all lenses wide open first, then stopped down 2 and 4 f stops. I look both for contrast and resolution when testing for sharpness, and color temperature variations and distortion (especially on a zoom). Distortion on a zoom doesn't necessarily mean I won't keep a lens, but it sure helps me know where along the zoom path I can expect to encounter its unpleasant effects. I routinely expect less than stellar performance from less prominent lens makers, or some of the older designs...but again, that doesn't disqualify a lens from use. Last year I picked up a 1960s Spiratone 400/6.3 for about $30, cleaned it up, machined a little on it and am now occasionally using it on a variety of my cameras. No, it doesn't match some of my Leica gear, but it is a great pinch hitter, especially where I have a tripod handy and am primarily concerned with the central field of the photo rather than the periphery. I'm planning to give it a good workout in the next several weeks photographing ducks for a local woodcarver.</p>

<p><em>How would you go about testing your gear?</em><br>

<em> </em><br>

The usual procedure is to take a number of pictures of brick walls, post them on various gearhead forums and then switch camera systems. Of course, you <em>could</em> just take pictures and print them and see if they look okay. A problem like Scott's would clearly show up.</p>

<p>All normal photographic camera lenses should produce a symmetrical image. That goes for sharpness and vignetting. If a lens is soft in one corner when photographing a flat target <strong>with the sensor parallel to the target</strong> then it should be equally soft in all four corners. Similarly the amount of vignetting, astigmatism, coma etc. should be the same in all four corners.</p>

<p>If it's not then the most likely cause is that one of the lens elements is tilted due to it not being properly seated in its mount.</p>

<p>The trick is "<strong>with the sensor parallel to the target". </strong>If the camera/lens is even slightly tilted to one side and/or up/down then that can (and will) cause asymmetry in the image<strong>.</strong></p>

<p>The only time you'd expect an asymmetric image is with a tilt/shift lens that's not properly zeroed.<strong><br /></strong></p>

<p>My motto is "I never met a $25 lens I couldn't fix in post".</p>

<p>I've accumulated 8 lenses since I bought my Pentax K100D four years ago. All under $100. Everyone of them will produce a great shot that needs very little post processing and everyone of them will produce a crappy shot requiring more than 15 minutes of post processing.</p>

<p>I never know what I'm going to get in image quality from these lenses no matter how well they pass the brick wall test. I can't explain it. I'm just glad I haven't had to pay over $100 to find out.</p>

<p>Just curious, but when your lens passes all tests that indicates it's a decent lens do you still get images that look like the sample below of a similarly lit scene and how much work do you have to put into it to make it look like the correction I've included?</p><div></div>

<p>Stephen you are great !</p>

<blockquote>

<p>photographing ducks for a local woodcarver</p>

</blockquote>

<p>I surely have ducks around, but there is a shortage of woodcarvers for a workout. </p>