Sony DT 18-250 max zoom

Started Jan 3, 2013 | Discussions thread
Chris Malcolm
Contributing MemberPosts: 857Gear list
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Re: Sony DT 18-250 max zoom
In reply to splashy, Jan 3, 2013

I thought the 250mm end of my Sony 18-250mm was rather soft until I started checking focus very carefully. I discovered that at 250mm the DoF was sufficiently shallow that a small backfocus error, too small to cause any problems anywhere else,  was causing the AF to misfocus at 250mm and f/6.3. Once I'd corrected that (or used manual focus) it was sharper.

On my A550 the AF also often misfocused it at 18mm, and I got sharper shots when I resorted to manual focus there too. That seemed to be part of general tendency of my A550 to underfocus wide angle lenses while being accurate at longer focal lengths. Once I'd discovered these errors in my A550's AF I discovered that my 18-250mm was a definitely better lens than I'd thought it was.

I also discovered by experiment that at all focal lengths f11 was definitely softer than f8, so if you're getting sharper at f16 I suspect focusing errors. If so, careful manual focus at f8 should get you sharper shots than you're getting at f16.

(Whereas my A77's AF manages to focus wide angle focal lengths much more accurately.)

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Chris Malcolm

 Chris Malcolm's gear list:Chris Malcolm's gear list
Sony Alpha DSLR-A550 Sony SLT-A77 Sony 50mm F1.4 Sony DT 18-250mm F3.5-6.3 Sony 500mm F8 Reflex +7 more
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