Lens QC

I have recently taken delivery of a new lens brought out by a friend from the UK – the DA16-45 – which from first impressions seems to have matched my high expectations, given its reputation. One reason I opted for the 16-45, as opposed to the DA or Sigma 17-70, was its reputed greater QC consistency. (A factor which becomes especially important when you are based in a country distant from where the lens is bought, and are therefore not in a good position to replace a defective lens). I have got the impression from various forums (including this one) that erratic quality control is a real issue with regard to lenses.

Anyway, to get to the point, I was wondering:

a. What forum members experience of quality control issues was? Have they had to return lenses often? If so are some manufacturers (or even lenses) particularly bad (or good) in this regard? From what I have gleaned it seems that Sigma has the worst reputation for QC; though some lenses from Pentax, notably the 16-50 and also perhaps the new 17-70, don’t appear to shine here either. Interestingly – given that, if I’m not mistaken, it has in the past had a reputation for producing rather cheap quality lens – I haven’t come across criticism of Tamron on this score, though this may be just coincidental (I can’t claim to have done in-depth research).

b. What do people do to check newly purchased lenses? I came across a thread on another forum that recommended the following test for focusing (http://www.focustestchart.com/chart.html); and for de-centered elements, taking pictures of a contrasty wall at varying apertures and (in the case of zooms) focal lengths. Does anyone have other suggestions?

It strikes me that having feedback on this issue here would be useful for forum members (not least me!).

Hi Mhuni,
I haven't had a duff lens yet... though my SMC-FA 24-90 came back from repair (having cracked the barrel) much sharper than before.
Some have had slight focus variations, true, but these are all easily resolved in the K20D.

A word of caution regarding the Focus Test Chart (very slightly off topic). In trying to setup all my lenses with the K20D I decided to try a different approach. I used a piece of Lego base board, with a "wall" sticking up to focus on. The "pips" on the base board can be used as a good indication of what's in focus - shooting almost parallel to the board, but not quite. What I noticed confirmed something I knew already - that the field of focus is not always flat
(In the case of the SMC-FA 50/1.4 it's obviously curved. The edges are in focus nearer the camera than the centre - if you adjusted using the edges then your centre point would be wrong )
For the Focus Test Chart this means you could be making a decision based on the edge focus field which may not truly represent the centre of the lens. In the end, the best approach (for me at least) is a willing volunteer - shoot with the lens wide open and focus using the centre point only. Focus on their eye.
If you have their nose and hair in the frame you can easily work out whether the lens is front or back focused. In the K20D adjust until the eye is in focus.

Just thought that might help
Matt

I haven't had a duff lens yet from either Pentax or Tamron (never owned a Sigma), so either I'm lucky or they're not as prevalent as reading some forums would have you believe...

As for testing, I simply use the lens for its intended purpose and if I get a fair proportion of pictures that I think are good then I consider myself to own a good lens. Pictures that come out badly are 99.9% of the time down to a faulty user rather than a faulty lens.

I have a Sigma 17-70 and in all honesty can say that it is tack sharp and focuses perfectly, I also have a Sigma 50mm macro and again it is tack sharp although this is a manual focus lens but a joy to use. I have had very few issues with lenses and like hefty1 says, they tend to get used rather than tested, after all that was the reason for buying them. If I found that I had an oviously duff lens then it would go back, but up to now I suppose that I may have been lucky with my purchases.
Harry

Interesting that in all the responses so far, noone has had to return a lens. Likewise with my 4 lens (though the kit lens does have a mild FF tendency). Perhaps - like crime - the 'problem' of rogue lenses is magnified by understandable complaints by an unrepresentative sample of people who have actually suffered one.

I think you've hit the nail on the head there. I have bought many, many lenses over the years and not a one has been faulty. Some I have liked more, some I have liked less, but all have performed as expected in a technical sense.

Had a faulty DA* 16-50 which has been replaced, and tested a brand new DA* 300 that was faulty out of the box.

I have bought 5 lenses since I started,from 3 different manufacturers ,with no problems at all!......I had a problem with my K20 though,terrible back focussing!.....there was a period on here some weeks back when sigma 10/20's seemed to have a problem,there again I have nothing but praise for mine!................

Yes, I've seen a lot of gripes about QC of the Sigma 10-20 - but when people get a good one, everyone seems very happy with it. I was thinking about getting a super-wide lens when I'm back in the UK at Xmas and was looking at this and the DA12-24. Unusually, from the photos on Flickr I actually liked the colour rendering of the Sigma better. Generally, my impression is that Pentax excels on this score (another reason I opted for the 16-45 over the Sigma 17-70).

I'm finding the 16-45 just great, by the way - a big improvement on the kit lens and it has fantastic colour rendering (though the kit wasn't bad either on this front). Thanks John (amongst others) for continually singing the praises of this lens (which also played a part in my getting it - alongside the current price, which made it irrestible!).