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Message: <blockquote data-quote="David Ellsworth" data-source="post: 1863771" data-attributes="member: 40206">I'll bet if the 100-400mm were programmed to have a f/6.7, it would be fully sharp at f/6.7.I wonder if you also have this experience, Tony: I find it easier to manual focus the 100-400mm with f/6.3 DOF preview activated, especially when using Live View. At f/5.6, optimum focus has a slight softness, and if I focus to get rid of the softness, then I'm front-focused. However, holding the DOF preview button handheld makes the camera more shaky, negating the benefit unless I'm on a tripod.Really, I wish my camera body had a DOF preview lock mode, so I didn't have to keep my finger on the DOF preview button. It's possible to do this using EOS Utility or eos-movrec, but that requires tethering the camera to a computer.You're lucky you didn't disassemble the smooth/tighten ring. It's got more than 500 bearing balls inside.I could try using those tilt/centering adjustments myself, but since my lens went through Canon repair it has a 6 month warranty. It would be a waste not to use this... hopefully if I escalate it to a supervisor, they'll do the job right this time.Even if I could adjust the tilt/center myself, the barrel play would still exist. So if it's adjusted properly for the equilibrium position (the way the barrel hangs when the lens is right-side-up), simply holding the lens in the wrong way while shooting could make it soft in the center and astigmatic in the corners and edges. I'm hoping that Canon repair can do something to reduce barrel play so I can hold the lens comfortably.None for me <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite3" alt=":(" title="Frown    :(" loading="lazy" data-shortname=":(" /> I've just got a 450D and a 40D.My 100-400 sometimes focuses perfectly, but in the field the AF often has front-focus. Another reason I need to send it in the Canon again...To keep this from being completely theoretical, here's a photo taken wide open at full tele with my 100-400. Not only was this wide open & handheld, but it was shot through a window (which can degrade shots). I love how the reflection of the sun on the Cassin's Kingbird's eye is a clean circle (with no flares coming out of it) because there are no iris diaphragm blades interfering with the light. (I also sometimes like the iris-blade flares in an eye highlight, but perhaps only when they're strong, from stopping down quite a bit.)The 100% crop is sharpened with an Unsharp Mask of 0.3 radius and 200 strength. Some pretty clean feather detail can be seen at (or at least very close to) the Nyquist limit (though the camera is just a 40D). <<<a href="http://picasaweb.google.com/davide.by.zero/Birdforum?authkey=Gv1sRgCKuourajqMzP-QE#5488819247819373186" target="_blank">full pic here</a>>>Oh, and I had a laugh catching this flycatcher perching on a seed feeder!</blockquote>

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