Frustrating issues with auto-focus. Need advice.

[scott-hall-images]

<p>I also shoot with a D7000 with the same lens (sometimes) but am no expert with autofocus. I shoot with the AF-S setting. Are you putting the square on the subject's face or shirt? I find the camera struggles a bit when focusing on a solid color but works great when there is more variation. I'll do some more testing with similar settings as yours. </p>

[robert_k1]

<blockquote>

<p>What is the deal? Camera defective? Lens defective? Do I need to tweak any settings?</p>

</blockquote>

<p>The AF system on a dSLR is very complex. The settings include: many buttons on the body and numerous options in the menu. Each of these would interact with the others. They are there for a reason: for each specific shooting situation (still life, sports, portraits, etc.), the AF can be fantastic IF ALL the settings are PROPERLY set up. But if ANY ONE is not properly set up for that particular situation, AF would seem to behave in mysterious ways. Many would blame the camera or lens.</p>

<p>Nikon (don't know about others) could have done a much better job helping the users (like they did with tip sheets for film bodies in the good old days.). Instead, the manual would describe each button and menu option, and how they interact with each other. But the number of permutations would soon get out of hand, and difficult to keep track of. A tip sheet from Nikon suggesting settings for each shooting situation would have been a great help. Without these, third party user guides and online tutorials are the next best things for the new owners.</p>

<p>http://www.bythom.com/nikond7000guide.htm<br /> http://www.nikonians.org/dcfp/user_files/85597.pdf</p>

<p>For better answers, OP should tell us exactly how each button and menu entry are set up.</p>

<p>This recent thread about locking focus and recompose may also be of interest.</p>

<p>http://www.photo.net/beginner-photography-questions-forum/00bsbr</p>

[William Michael]

<blockquote>

<p>Or maybe zoom in, lock focus and zoom out!<br>

+<br>

I <em>wouldn't</em> zoom in, lock, zoom out - I can't speak for your lens, but on a lot of lenses this causes a small shift in focus position.</p>

 

</blockquote>

<p>If you are still reading this thread . . . I agree that this is a bad idea generally, unless one knows <strong><em>exactly</em> </strong>how the lens will perform: but more specifically for your situation -</p>

<p>Many (most, nearly all?) DSLR zoom lenses are <strong><em>varifocal</em></strong>. That means they do NOT hold focus through the zoom’s compass. Lenses which do hold focus through the zoom compass are termed <strong><em>parfocal</em></strong>.</p>

<p>I am very confident that your Sigma lens is varifocal.</p>

<p>WW</p>