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Old Apr 30, 2011, 10:25 PM   #1
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Default Manual vs Auto Focusing

I was experimenting today and noticed that manual focusing was not as good as auto focus. I have a Sigma 28-300mmD lens on a Nikon D7000 body. Manually focusing so the image was razor sharp in the viewfinder produced an image that was really not in focus at all. Then I switched to Auto Focus and the image was much improved. Shouldnt I get what I see in the viewfinder, as far as sharpness due to focus? I was shooting a bird and paid particular attention to the details of the feathers. Auto focus was way better than manual focus. Does anyone know how this can be fixed? I prefer to go manual most of the time.
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Old May 1, 2011, 4:17 AM   #2
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It's may be your your diopter adjustment.

BUT, without a split prism focusing screen it's very difficult to tell what's in focus using an optical viewfinder with a modern dSLR

I've read that it's virtually impossible for the human eye to distinguish correct focus with as hallower depth of fields without a split prism focusing screen (with accompanying math showing apertures you can expect to be able to focus at, and why the eye can't see well enough to focus with shallower depth of fields).

IOW, the optics are going to limit what the eye is capable of focusing accurately; in the same way you can look at a smaller image on a camera's LCD and think it's sharp (until you view it on a larger display and find out that it's really blurry from being out of focus or from subject movement/camera shake).
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Old May 1, 2011, 9:01 AM   #3
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I have that problem with the viewfiner all fuzzy...then realize I don't have my glasses on. Amazingle, the photos turned out in focus when I didn't have my glasses on.

Diopter adjustment could be an issue, and I use to lament the lack of a split prism focusing screen, then somebody told about the lights. They substitute for the split prism. On the D90, the "in-focus indicator" is the first item on the lower bar in the viewfinder, but only lights up when in focus.
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Old May 1, 2011, 9:57 AM   #4
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Certainly, the diopter adjustment on the eyepiece can increase the accuracy of your efforts at manual focus, but autofocus is usually more accurate than manual focus.
  • The lens is the thing.
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Old May 2, 2011, 3:09 AM   #5
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i read somewhere that when using manual focus most cameras will still light up or beep to let you know when its in focus.
so i thought well i might as well just let the camera do the lot then and turned autofocus on
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Old May 2, 2011, 6:44 AM   #6
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Thanks for your comments guys. I think I will be playing with the diopter now. Id really prefer to use manual focus if I have a choice.
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