Front Focus issues

InsuredDisaster

I bought a Sigma 30 1.4 for my Nikon D300 and found it suffered from front focus. So I dialed in about 15 for the AF fine tune. Its now pretty good. However, I found that the Nikon 50 1.4 looks clearer with 15 tuned in as well, though I'd never notice it without having been looking specifically for it.

(I was doing this test at 1.4)

My questions: Both the 50 (nikon) and the Sigma look better with the AF fine tune, though I've not tested it with all of my lenses (I will.) But the Sigma looks horrible without the fine tune. So, is does this indicated superior glass in the Nikon? If the camera is 15 off for all of my lenses, can I/ should I have the camera retuned?

I'm going to look at the D70 with the lense as well to see if it also seems less sharp.

Otherwise, the Sigma is pretty nice. To of course live up to Sigma's spotty QC, the HSM focus on my 10-20 is silky smooth. The 30 feels gritty. The 18-200's zoom sticks.

My nikons (50 1.4 and 70-200 2.8VR) are of course wonderfully sharp and perfect.

ziggy53

You are correct to use the 2 bodies to try to diagnose the problem. Use a tripod and static scenes at first (with center focus dot only), interchanging bodies. Remember too that the D300 is more densly populated with pixels so that differences at 1:1 display are more "magnified" on the D300 versus the D70.

You may want to interpolate the D70 images to the resolution of the D300 for a more direct comparison.

InsuredDisaster

I tried the D300 and the D70 with all lenses on the tripod using remote releases, etc. The Sigma 30 does ok on the D300 with its superior AF and fine tuning, but on my D70, it is very hit or miss. Since I want to be able to put the faster 30 1.4 on the D70 (noisier at higher ISOs) and other lenses on the D300, I'm going to see about returning it for another copy and this time bring the D70 long to make sure that it works

On the D70, its often twitches back a bit in AF-C and AF-S and this can make it unusable.


Once properly focused however, the Sigma 30 does not have the nasty color fringing that the Nikon 50 has.

Oh by the way, after using the tripod and my computer I realized that the Nikon 50 did not need the correction for the AF fine tune. While it was undeniably sharper in the store on the D300's monitor it did not seem so once on the tripod.