Techniques, Reviews and Commentary
18-55 OSS The Tricky Stuff
The Sony 18-55 OSS zoom is by no means a great lens, but it has some good points, it looks neat, is nicely put together compared to most kit zooms, costs next to nothing, is good to manually focus and for the intended purpose is sharp enough. Importantly it also works well for video and has a reasonable macro capability.
Of course there is nothing you can do to tame the woeful edges and corners at 18mm nor the soft edges at 55mm, both of these are kind of fixed issues unless perhaps you are prepared to shoot at f16 and put up with the softening effects of diffraction.
I wouldn’t want to be stuck with an 18-55 OSS as my only lens option but if I was I could pretty much get the best out of it. Now since there are thousands of these little silver jobbies out there it might be helpful to some people to know how to wring a little more out of the device, so here are four pointers that should help.
1) It is a true zoom, meaning that it holds its focus point as you zoom, and don’t assume that all so called zooms are true zooms, many are not. How might this be helpful?
For landscapes you may well be able to get far better focus if you do the following.
Zoom to 55mm in manual focus, then focus on an infinity object at your intended aperture, (a distant tree is a good choice). Adjust the focus until the tree or other item is just in sharp focus, then zoom back to whatever focal length you require.
This of course gives you very fine control over the focus if you use the fully magnified view, which is what I use and recommend.
I was, I must admit a little surprised That images focused this way seem to be a little sharper across the board. I expect it might have something to do with field curvature playing with the focus under normal circumstances or perhaps the focus system is fooled by contrast variations under some circumstances, regardless landscapes created this way are reliably sharp.
2) If you leave the camera in manual focus and then switch it off the focus will remain in the same position when you next turn your Nex on. Sounds like the bleeding obvious, not really, many cameras still drive the focus motor upon start up regardless of the focus setting, for example the Sony Alpha 900.
Having the focus lock into position is really quite brilliant because you can set a zone focus or the hyper-focal distance and the focus then holds when you shut down but is ready to fly on start up. Importantly with the Nex and Sigma lenses bumping the focus ring when shut down will not shift the focus.
The really neat thing about manual focus on the Nex is that you really have a very fine level of control/ accuracy and trust me that is not the case with most kit lenses that are almost all universally sloppy and far too touchy to give totally accurate manual focus position.
3) Having tested the performance of the lens at all focal lengths it turns out, on mine at least that 26mm (not 24mm as is commonly believed) is the absolute best setting in terms of quality and f7.1 the best overall choice of aperture for across frame clarity without having diffraction knock the edge of your image.
The performance at this setting is actually very close to the sigma 30mm f2.8, but of course you don't get the Sigmas choice of being able to shoot at any aperture and still get a sharp image.
As a bonus at this focal length there is virtually no distortion and very little if any vignetting, best of all however the CA is also at its lowest level bang on 26mm.
In truth choosing 26 mm and cropping a bit will probably give a superior result to say choosing say 30-35mm instead!
By the same token 26mm is probably a good choice for sweep panoramas and definitely the best choice for regular panoramas as the lack of distortion and superior cross frame clarity will make the stitching process more successful and less prone to joining errors.
Don’t rely on auto focus accuracy for infinity focus. I have found through a number of repeated tests that often the auto focus does not nail the infinity point unless the zoom is set to maximum focal length and even then can misfire ever so slightly. Normally it gets close but going into DMF reveals at the magnified view that it is often out by just a little bit and in the case of the wide angle setting can be quite wide of the mark which of course exacerbates the already poor level of cross field clarity at the 18mm end of things. With it being so easy to use DMF it makes sense to have this turned on most of the time and habitually do a little check prior to clicking the shutter.