From: "Amy Hughes" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, December 10, 2004 8:28 PM Subject: Re: backfocus (was: Survey:istD reliability)
> > Amy, what focusing mode are you using? > > I'm having this problem with manual focus, hence my temptation to > believe it's my fault. I don't know if it's also a problem with > autofocus because I don't use autofocus. > > What I am finding fairly often is that the "acceptable focus" covers > from the point I focus and a bit beyond, when what I'd expect it to > cover is the point I focus plus/minus. > > Here's an example, though it'll be difficult to judge after > resizing/compressing... > > http://www.amyhughes.org/lego/conventions/IceCreamShop/IMGP0351sm.jpg > > I was focusing on the front of the building, right under the awning. > It's pretty well focused front to back, all along the side, but the > figure standing right in front of it isn't. The guy in the blue overalls > is in focus, the guy in red isn't. I don't know if I've misssed something here, but to me it simply looks like you've been using too wide an aperture, and really can't expect the objects mentioned close to you to be in focus. You may simply have to stop down a few more stops, if possible. (Generally there is a narrower area of focus in front of the selected point of focus than behind it, why you'd want to focus on the nearest subject that you want to be in perfect focus.) As far as I can see, the wall which you focused on is in perfect focus, why the camera seems to me to be working correctly. > To test if I was still capable of focusing a camera I shot a narrow DOF > picture of a piece of graph paper on an angle, and the line I focused on > was properly focused. So I'm capable and the camera is capable, but I > haven't figured out why so many of my shots aren't properly focused. > > When I shot jewelry the fabric I used as a backdrop was perfectly > focused and the piece I was shooting wasn't. Repeatedly. I don't know the distances to, or the sizes of, the jewelry pieces you shot. Your problem could be that for some reason the camera used a focus point that you were not being aware of (if in autofocus mode). When shooting at close distances the DOF gets (relatively) narrower than you'd may think, and you will have to stop down. This is a particular problem when shooting macro for instance. I'd suggest you'd do some very systematic tests. For instance you could shoot a line of nails upright at a distance of say a feet apart in a piece of wood (maybe numbered by some sort of "stick on" pieces of paper). If you got any you could also place one of those measure.... (what are they called - indicating inches, feet or centimeters and meters) alongside it slightly tilted to your shooting angle so that the numbers will be clearly visible. Pick an aperture, let's say you start at 22 (and the next round you open up two stops etc), and carefully focus in on the first nail (nearest to you). Repeat this for each nail. Than pick another aperture and repeat the process. Evaluate your results. If need be post the results and I think we will be able to tell what it is that's not working right for you. Good luck, Amy. Lasse > Amy >
