[interested_observer]

Warning: This is a Geek Level 3 article. If you aren't into that kind of thing, go take some pictures.

I've been writing and discussing the copy-to-copy variation that inevitably occurs in lenses since 2008. (1,2,3,4) Many people don't want to hear about it. Manufacturers don't want to acknowledge some of their lenses aren't quite as good as others. Reviewers don't want to acknowledge that the copy they reviewed may be a little better or a little worse than most copies. Retailers don't want people exchanging one copy after another trying to find the Holy Grail copy of a given lens. And honestly, most photographers and videographers don't want to be bothered. They realize lens' sample variation can make a pretty big difference in the numbers a lens tester or reviewer generates without making much difference in a photograph.

• LensRentals.com - Measuring Lens Variance

What Are We Going to Do with This?

Fairly soon, we will have this testing done for all wide-angle and standard range prime lenses we carry and can test. (It will be a while before we can test Sony e-mount lenses - we have to make some modifications to our optical bench because of Sony's electromagnetic focusing.) By the end of August, we expect to have somewhere north of 75 different models tested and scored. It will be useful when you're considering purchasing a given lens and want to know how different your copy is likely to be than the one you read the review of. But I think there will be some interesting general questions, too.

• Do some brands have more variation than other brands?
• Do more expensive lenses really have less variance than less expensive ones?
• Do lenses designed 20 years ago have more variance than newer lenses? Or do newer, more complex designs have more variance?
• Do lenses with image stabilization have more variance than lenses that don't?

Before you start guessing in the comments, I should tell you we've completed enough testing that I've got pretty good ideas of what these answers will be. And no, I'm not going to share until we have all the data collected and tabulated. But we'll certainly have that done in a couple of weeks.

[normhead]

This is the place where you find out your copy of the 18-135 being better than your copy of your 16-50 is not because in general it's a better lens, it's because you got a really good 18-135 and a really bad 16-50 but they are both within spec.

[tibbitts]

This is an important subject, thanks for posting. It will be interesting to see the full results.

[osv]

thx for the link.

in real-world use, this is what lens copy variation looks like: 24mm lens copy variation testing, Sigma SuperWide II and Canon FDn 24/2.8

when you can see those decentering differences at f/8-f/10, it'll usually be much worse wide open.

copy variation is a really big problem.

[jonby]

I agree that copy variation is a pretty important issue. My personal view is that variation is currently higher than it should be generally. I can't speak for others, but in my case this wide variation has certainly led to me making fewer lens purchases than I otherwise would.

I have no doubt that the more stringent controls over construction needed to reduce variation must come at a significant cost, raising the price of lens manufacture and therefore probably retail price, put personally I would be prepared to pay a bit more for the peace of mind that the lens will perform close to its optimum. Certainly with the more expensive lenses, I really think it's unacceptable for consumers to effectively be taking part in a lottery for items costing many hundreds of dollars/pounds. Since most lens purchases are done remotely these days, it's even more important that these issues are improved, as sending lenses back and re-testing new copies several times becomes a time consuming business which you really shouldn't have to go through. You're really doing the manufacturer's work for them. A lens's optical performance is so fundamental to its value that I do think it's unacceptable that tolerances seem to be so loose.

Although I may get flamed for saying this, my subjective impression is that Pentax is not the best in this regard, based on my own usage of different systems, review reading and analysis of samples. It will certainly be interesting to see LensRentals' test results however.

In the samples posted of the Sigma and Canon 24mm lenses, it's clear that there is significant variation, most notably in edge sharpness and centering. This corroborates my own experiences generally with lenses (ie. that edge sharpness and centering is where they vary the most). In these tests, the Sigma shows the largest variation, with one side being a lot sharper than the other in two of the samples. The Canon does vary a bit too, but not as much. Both lenses perform pretty well considering their age and the high resolution of the sensor though.

[normhead]

Just wondering, what Pentax lenses you've had decentering issues with?

[everydaylife]

This is the place where you find out your copy of the 18-135 being better than your copy of your 16-50 is not because in general it's a better lens, it's because you got a really good 18-135 and a really bad 16-50 but they are both within spec.

I had this experience with the Da* 200. The first new copy I bought I was, from the very first shot, gobsmacked by the image quality. Sharp, contrasty, great rendering and this was wide open. Unfortunately after only a week there was a fault and instead of getting it repaired under guarantee, I did not want to wait 3 or more weeks, I exchanged it at the shop. It was a big mistake because the copy they gave me did not have the same image quality. I took it to Pentax they agreed about the difference but said it was in spec but would try to find one as good as the first. Six months later I had used 6 copies and all were slightly different but none were as good as the first copy. One would pf more than the other or be softer than the other. Interestingly this includes two copies that were lent to me by Pentax. One copy was a little soft wide open but had little to no purple fringing. The other loaner copy just had too much PF. I never did find one as good as the first copy but the one I have is good enough.

The thing that disappointed me was that the star lenses are supposed to be the best lenses in Pentax's range and yet there was such a variation in quality.

So this experience taught me what the phrase ‘it’s a keeper’ really means. My very first copy was an exceptional copy ‘a keeper’ only I did not realize it at the time and exchanged it. Damn!

So now when I see postings with stunning images waxing lyrical about the new lens they have just bought I wonder do all copies perform the same or have they got a ‘keeper’?

[osv]

i tested four brand-new copies of the korean 35/1.4 lenses, they were all defective.

wide open would typically be very good to extremely impressive, but close down one stop, and there would be oof areas through f/4.

i kept thinking that i'd get lucky with this lens roulette, but after i rolled the dice the fourth time, and got a badly decentered version, i gave up on it entirely.

here is what it looked like at f2: https://www.dropbox.com/s/0gxrx5uebxgstlk/DSC03353at2point0.JPG?dl=0

[jonby]

Just wondering, what Pentax lenses you've had decentering issues with?

DA16-45, DA18-55, DA50-200, FA28-70, M35-70 2.8-3.5, F35-70.

All fairly low-end zooms admittedly, but all exhibiting pretty poor sharpness on one side/corner or another, even when stopped down, usually worse at certain focal lengths than others.

I'm certainly not saying that Pentax are the only culprit, but I have to say that I haven't observed these problems to the same extent in Canon's 18-55 mkII lens, despite its subjectively awful construction, and I have used multiple copies.

The first copy of a Samyang 14mm I bought exhibited quite strong alignment issues (manifest as a diagonally receding focal plane). I returned it and another copy before settling on one which was 'good enough'. All had different properties, with quite wide variation in centre sharpness wide open, as well as some strange focal plane characteristics. The distance scale was way out on all of them, to varying degrees, though that's not such a huge problem. The whole thing took quite a while to sort out, and felt like a bit of an ordeal. It also led me to wonder what the retailer did with the returned copies. I presume they just sold them to someone else.

The thing that disappointed me was that the star lenses are supposed to be the best lenses in Pentax's range and yet there was such a variation in quality.

I feel your pain. Yes at this price level, I really think that manufacturers need to be enforcing tighter tolerances than this. There must be others like myself who are put off spending hard-earned money on lenses when it's such a lottery.