Testing the 18-55mm kit lens.

How do you folks go about lens testing?

I've commented on here before about the 18-55 kit lens being poor so I did a quick test at home, taking shots of a bookcase in my study from a couple of metres away. I did the following tests:

1) At 19mm against a cheap 19-35mm Pheonix AF zoom (same as the Vivitar and Cosina one).
I tested wide open (f3.5) and at F5.6, F8, F11, F16 & F22 looking at the centre and corners of the frame. At all apertures the 18-55 was noticeably sharper that the Pheonix in the centre of the frame but it was a different story at the corners where the Pheonix was a lot sharper. On both lenses the sweet spot seemed to be F8-F11 (f22 was quite bad with both). The colour rendition looked better with the kit lens.

2) At 28mm against the Pheonix again and also against a SMC-FA 28-200.
Again the kit lens gave the best centre sharpness of the the three but the worst corner sharpness. The SMC-FA 28-200 was the best of the three in my opinion, and also had the best colour rendition and contrast.

3) At 50mm against the 28-200 and a SMC-M 50mm F1.7
The difference in sharpness across the frame between the old manual focus prime and the two zooms was remarkable. There wasn't much in it between the zooms at this focal length.

Overall the kit lens delivers reasonable centre sharpness but is very soft in the corners, especially when outwith the F8-F11 aperture range. It reminds me quite a lot of my very first Pentax lens in fact - the old powerzoom FA 28-80. I think the reason I've been more dissapointed with these lenses than others using them might be because I often shoot outdoor wide angles from low down with an object of interest near to the camera in the foreground. The lack of corner sharpness means that the foreground object is quite soft, however if you were placing your main point of interest in the centre of the frame then you'd probably be a lot happier - for example I've found the kit lens gives decent portrait results.

If you're after a quantitative lens test then you really need a decent lens test chart. These are available commercially, or you can find them on the web: the most commonly used is the 1951 USAF test target which is available here: http://medfmt.8k.com/mf/USAF.pdf among other places.

Instructions on how to use the chart can be found here:

http://www.takinami.com/yoshihiko/photo/lens_test/pdml-procedure.html

The USAF chart has a number of shortcomings, but is very widely used. One improved chart can be found here: http://www.normankoren.com/Tutorials/MTF5.html along with lots of lens testing links.

Steve

http://www.stevewilde.co.uk/
http://www.siblingmedia.com/

Excellent thanks, that's very useful. I'll re-do the tests based on that info.

I'm certainly far from being an decent lens-tester but I ran my own personal unscientific test comparing the kit lens at 35mm against the FA 35/2 at different apertures and I found pretty much the same results that you described. Sharp in the center, very soft in the corners. I also found some vignetting in the kit lens when used wide open. Even though I'm just testing the kit to justify spending my salary in a DA 16-45, so far I think it is not bad for Ca$100...

(Fernando: and the DA16-45 is positively outstanding )

Here's my unscientific approach to lens testing....Don't Bother.
I read some tests and reviews, get some opinions, and whenever possible try it out, before making a purchase.
Once I got it, I use it, and use it, and use it.
I evaluate it, based on the images I like, and learn what it does well and does not do well, and then call it into action whenever the situation demands that piece of equipment's best features.
Same goes with managing people, find out what they're good at, and put them where they'll do the most good.
When somebody starts saying "low contrast, low color saturation, soft" about a lens I start thinking "Hollywood, '50's, Glamour, Portraits"

I have not doubt about it, that's why I want one so bad, not only I've been consistently reading the same excellent reviews everywhere but I also found this:
http://www.pictchallenge-archives.net/BxuREV7.html
My french is not good but the results look pretty sharp

PS: My plan is to include the cost of the 16-45 as part of the vacation budget... wish me luck

BTW that was me (forgot to log in)

I've done the first couple of tests of the 18-55 now. This was looking at ultra-wide performance compared with the only other lens I now have covering a similar focal range, a cheap Pheonix 19-35mm (same lens as the Vivitar and Cosina) I used to use with 35mm film.

The camera was mounted on a sturdy Manfrotto tripod and head and the 2s mirror up setting was used on my DS. I had two of the targets set-up - one in the centre of the frame and one in the corner.




Centre of Pentax 18-55mm at f3.5




Centre of the Pheonix 19-35mm at f3.5




Corner of Pentax 18-55mm at f3.5




Corner of Pheonix 19-35mm at f3.5

Centre of Pentax 18-55 at f11




Centre of Pheonix 19-35mm at f11




Corner of Pentax 18-55 at f11




Centre of Pheonix 19-35mm at f11

Interesting, although don't forget that lenses are designed to work at particular distances and close up to a lens chart will not be ideal for a wide angle zoom.

The charts were at a distance similar to where one might place the foreground interest in a wide angle shot, so I think it is important that a wide angle lens is capable of sharp results at short ranges. The tests do back up what I'd thought of the lens in use though, in that I've found it ok for snapshots but very soft.

I repeated the tests at 28mm, this time also including the SMC-FA 28-200. Wide open at F4 there wasn't much to choose between the 28-200 and the 19-35, however the 18-55 was noticeably softer in the centre and in the edges.

At F11 there was very little in it between all three lenses.

One thing I noticed in both sets of tests was that the 18-55 produced a slightly darker exposure than the other two, despite the same aperture and shutter speed being used.

I think you're doing the right thing - there's no substitute for testing your own lenses for the purposes you wish to use them for.