Sigma 70-200 sharpness issues, warranty?

[BLWNHR]

September last year I had all my gear stolen (D300 and 10-20, 24-70, 70-200 Sigma's), it was all replaced on insurance no problems. I added some of my own money and moved to a D700, Nikkor 16-35VR, Nikkor 24-70 and Sigma 70-200. I chose the Sigma again because my stolen one was exceptional and I couldn't stretch the budget to a Nikkor version.

Since getting all the gear I have changed what I shoot quite a lot. I used to do a lot of motorsport, but now I do more portraiture and landscape work. As such I haven't really used the 70-200.

The times I have used it I have noticed it isn't as sharp as my old copy, the zoom ring is stiff and it suffers more CA's than the one it replaces.

Does anyone know what my options are here? It was bought from a local store (not a grey import) last October, so is under 12 months old. It isn't convenient for me to get into the store I bought it from for about the next month, so I thought I would ask here.

I get along with my local store really well, but do you think CR Kennedy will want proof of my claims if it is sent back?

Something I'm not really sure of, would the move to FF accentuate CA's? Or is that something fundamental in the lens?

[kiwi]

Adam, Id just ring CR Kennedy and have a chat to them about it, see what they recommend ?

[gqtuazon]

It's a hit or miss with Sigma. I only have one Sigma lens and it's calibration is spot on. Your best option is what Kiwi had suggested. If that doesn't work, then you'll normally have to send both camera and lens so that Sigma can check the calibration issue unless you want to do a AF fine adjustment with your D700 which what I frequently do with my prime lenses but I have not tried that process with the zoom lenses. The Sigma 70-200mm f2.8 is much lighter than the Nikon which makes it a lot easier to use or carry sometimes.

[Lance B]

Have you checked that it isn't front or back focusing?

[arthurking83]

I wouldn't classify the Sigma as much lighter than the Nikon lens, in fact without a direct comparison between the Sigma Tammy and Nikon lenses, you'd be hard pressed to feel any real significant differences between them all.
Nikon feels more solid, Tammy more plasticky and Sigma half way between the two.

I'd be inclined to do as Lance says, and check for focusing accuracy. Easy to do, takes a bit of time, as you should really check focus at a few different focal lengths... say 70mm 105mm and again at 200mm.
Don't get into the same trap that other do and use miniumum focus distance, try focusing on something smallish at 200mm and about 4-5m away, making sure that the subject matter fills as much of the focus square as possible, and that no other subject matter is going to confuse the focus point.
Good subject matter for that focus distance includes items like a box of matches, a small lunchpack sized pack of sultanas, etc...

Because the Sigma lens is HSM, all you need do is(with lens mounted on a tripod!!!) completely defocus the scene(set focus to infinity) and then hit the focus button. If you set the camera to AF-C, then don't hold the focus for too long as the camera may be inclined to refocus slightly(this can lead to misleading focus innaccuracies as the system may be reacting to a user input). If you set it to AF-S mode the confirmation beep should stop the focus system.
Nopw before anything else, switch to LiveView mode and then zoom the preview screen to 100% view(one stop before the last zoom level, the final zoom level is set to 200%). once in Lv mode, simply flick the fopcus ring either way to see if you cvan achieve a better focused image. Simple procedure, can take a few attempts to do it consistently right, and if it needs any tweaking to get a better focused image, you can then to a micro adjust test to determine the best level of focusing innacuracy.
Once you get to this point tho, it's best to get the lens/camera calibrated rather than set any micro adjustment in the camera(for a zoom lens).