>I have read before that Nikon's pro lenses are usually spot on >and do not require focus tuning on the higher end Nikon >bodies. I include the D300 in that. I shoot with a D300 and so >far I've been very pleased with the focus accuracy of my pro >lenses. I'm now wondering whether I may get even better >results by focus tuning. My D300 had had a recent service, and >it focus calibrated, so it should work perfectly with pro >lenses, surely.
What we are talking about here is a system with two components, in theory either element of that system could be off slightly or both elements. For me focus tuning started with my 500VR and my D300 where I encountered a clear pattern of otherwise sharp pictures with the focus zone was forward of where I wanted it. I.e. for a Redpoll perched on a branch and its head as the focus point, the elements of the branch closer to me than the birds head were in sharpest focus. In order to detect this problem I had to have a lot of experience with the lens and I had to be getting myself into situations where I was close to the bird such that the depth of field was shallow enough that the issue could be noticed.
So I try to caveat focus tuning to situations where you've detected a clear pattern in multiple shoots and the photos you are using to detect the pattern are otherwise sharp, it's just the zone of focus you want to push back or pull forward. Sometimes people use a completely unsharp photo as an indicator of a need to tune, but that almost certainly a wrong motivation for tuning.
> Can I ask how many of your pro lenses, > particularly your 500mm f4, needed adjustment?
The 500 f4 given it's razor thin DOF is the one that needs the most vigilance. At 30 feet with a 1.4 teleconverter DOF is 1.3 inches. Compare this to an f3.5 - f5.6 18-55 zoom which requires the least vigilance given its 277 inch DOF! Or an 18-105 which has 67 inches of DOF at 30 feet. http://www.dofmaster.com/dofjs.html
Once I started tuning I naturally progressed to the 70-200 since in it's main use for me, I shoot it wide-open.
f1.4 lenses should likewise probably be tuned for the same shallow DOF reasons. So really you are looking at f2.8 telephoto zooms, f1.4 lenses, and super-telephotos as being the main lenses to consider tuning.
Tuning is a big job though, multiple lenses and 3 cameras and two teleconverters means a lot of permutations
> I was also >under the impression that focus tuning a zoom lens was a >thankless task, due to the a variable focal lengths. What >might be good at 70mmm, may not be as good at 200mm, and >vice-versa. I would be interested to hear your opinion on >this. Thanks in advance.
I realize people raise this as an argument for not tuning, but the very same issue applies to your fresh from the factory lens and camera too! I.e. it comes from the factory with a certain calibration and they must have had to pick a focal length for that In light of this, what people commonly do for tuning is shoot at longest focal length and wide-open on the theory that that is where the lens is least forgiving. After tuning, I keep a close eye on the real-world results at all focal lengths just in case.
I saw a recent article from Thom saying he repeats his tuning over time and for example just prior to a major trip such as an African safari. He does this on the theory that jolting and banging about can cause calibration to change.
And if you want to talk about tight tolerances, highly experienced DigiLloyd can evaluate whether the left vs. right side of images have what he calls "Brand New Blur". Lloyd Chambers is beyond my level of expertise, but he actually does advocate we test our brand new lens to make sure they are not decentred, or our camera lens mount flanges are not out of whack. I don't have quite Lloyds testing skills but given the cost of some of this equipment I do try and do some brick wall testing of my new lenses nowadays. (But also be aware brick wall testing is not a good subject for lens tuning, for that you need a subject with depth to it).
Anyhow I try and not let this topic get away from me, I don't want to spend all my free time tuning. But I do want to get the most out of my shoots so lens tuning is just one part of the package as are all the other shot discipline, VR, or high shutter speed techniques we use.