Focus issue Nikon D300 ore faulty 17-55 F2,8?

Started Jun 25, 2008 | Discussions thread
G Davidson Regular Member • Posts: 166
Re: Focus issue Nikon D300 ore faulty 17-55 F2,8?

Here's an update, in case anyone searches for this- which I think is a relevant issue for anyone using DX, for which the 17-55mm is Nikon's first and perhaps last attempt at a standard pro zoom. After checking the lens, Nikon said that there was no problem with it, but that there was some dust on my AF sensor that may have been affecting autofocus. Now this dust would probably be a recent development, long after when I first got my 17-55mm back from being fixed. Which leaves me with two, not necessarily exclusive, possibilities-

1) My technique is flawed and, especially at longer lengths, I'm getting blur from camera shake. This is quite possible, as I often shoot at 1/60, which on an 83mm lens (equivalent) may not always be enough for me. Yet as I had trouble focussing on a tripod in my home on some targets, it's not the whole story.

2) The AF-S, whilst being fast and near-silent, isn't all that accurate in challenging situations. I found my relatively slow Tamron 17-50mm II (non-VR) could accurately focus, even away from the center bank of cross-sensors, albeit with a lot of chattery hunting. The Nikon locks on very quickly, or at least claims to; but if the contrast and light aren't good enough, it can be a false confirmation.

I asked about it and Nikon did give me some advice about autofocus generally. One thing is to watch out for situations of low contrast, or when there are lots of similar objects. Another is to rely more on the cross sensors. I'm glad I asked, as knowing the limitations makes it a lot easier. Despite all the focus-points, I think focus-recompose is still the best way to get a lock on the target you want. With AF-S being so fast, this is even more important.

From thinking it was straightforward, I'm now seeing that the 17-55 is basically a tricky lens to use, if you want the best results. It gets very long for a non-VR lens (further than the 24-70mm does on FX) and is quite bulky, so hard to really stablise on a body. Maybe the D3 is the optimal match- the D300 being good, but not perfect. Also, I think my informal AF tests were sound- it focuses very quickly, which is great, but it would rather focus on something else than hunt when it isn't sure. I'd say this isn't just my camera's settings, it's the way the lens AF is communicating with the body. At telephoto, this problem is exacerbated, especially in low light and I get a lot of backfocus.

I remember the new 50mm f/1.4 G coming in for a lot of criticism for it's AF-S being slower than the D version's, though also being praised for it's accuracy, which at f1.4 is all the more important for it. Being an event-oriented lens, it seems Nikon went to the other extreme for the 17-55 and I can't trust it to get it right without babying it along. It seems even at it's high price, there are no free lunches as to it's capabilities. After all the tests and repairs mine has been through, I'm going to trust Nikon that this is as good a copy as exists. The only solution seems to me to be to focus on high-contrast details in the same or a similar plane of focus.

Personally, I think Nikon will update it with a VR version, like everyone else has and also that the optics will suffer a bit, as in-lens VR doesn't work to well or wider lens designs. Now that VR is more commonplace, this is just too long a lens to be left without it. I'm not so sure they'll bother with the nano-coating, as they probably don't want DX to be pro, just enthusiast-level. I'm also not so sure many people will care, so long as the results are good enough. This is a lens more similar in it's abilities and actual DOF to the 24-120mm f/4 than to the state of the art 24-70. Of course, if Nikon might not make it, but I tend to think they will see the market, even for prosumers, for a fast normal zoom that's competitive. Sitting back while people buy Tamrons or Sigmas, hoping they 'level up' to FX doesn't seem to me to be the best business policy and I think Nikon are catching on (though making a very affordable FX camera could work just as well, let's see).

Until then, would I recommend the 17-55? Well... it's still worth using for those who will put the effort into getting the best from it. I'll be using this whenever I have an event job, as it has to my mind very good (if not stellar like the 24-70mm) image quality and is great at short distances. Having the fast AF and the useful range is a necessity for me here, which nothing else gives me, so I'll work around it's limitations with techniques. In other situations, like travel, I'll keep using my Tamron; which is an excellent lens and so much lighter. I'm even thinking of getting the 16-85mm, which despite being a bit dark on the long end, gets so much praise.

Overall, I'm a bit disappointed about the AF issues, but then again my expectations are now that much more realistic. I'm also wondering if DX is a bit more limited in this respect than FX, as less light reaches the sensor. I certainly find it hard to accurately manual focus. Having a smaller sensor makes DX much more technology-dependant than FX; it's harder to get a bright lens and to have wide-angles that don't distort. The small image makes it harder to do accurate MF, which means we have to trust AF. By making such a serious attempt to get this right, the 17-55mm is an interesting lens and a very versatile one.

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