Manual focus: how can I tell if the subject is actually focused?

[ziggie216]

For example this picture that I took
http://upload.yasws.com/files/1/IMG_6622.jpg

I had to use manual since the camera could keep focusing on the background instead of the keys, but then I couldn't tell how much of a minor adjustment I needed.

[mattyb240]

Well only you know what you want to be focusing on right? So when they are sharp I guess is the obvious manor. If you cannot tell, find an object at the same distance which is bigger and clearer to see.

[Goshawk]

The modern DSLR do not really support manual focus. As said you can only go on sharpness. So you need good eyes. Live view is also handy for manual focus as the image is much larger thus easier to check sharpness. Not all camera bodies have live view though.

[chauncey]

ziggie, you had to much competition for the AF to lock in on.

next time...choose an item in the scene of equal distance, depress shutter halfway and recompose.

The "throw" of modern lenses make it difficult to manually focus.

[tzalman]

Using auto-focus would have been easier if you had found a better angle without all the distractions in the background, but if that was impossible, in the example posted you could have selected the focus point closest to the top of the portrait orientation frame and locked focus on the highest key which is against a background of sky or even on the tree branch.

[DStanic]

My advice- don't bother using MF on a Rebel. The viewfinder is too small and dim to properly see anything.

[RDKirk]

There is a trick you can use with those notorious "inaccurate outer focus points" that can solve such a problem.

The outer focus points (the rectangles) are sensitive only to subject contrast lines that run perpendicular to the orientation of the rectangles. That is, the vertical rectangles can only focus on horizontal lines and the horizontal rectangles can only focus on vertical lines.

So if the subject you want to focus on happens to have a strong linear component (such as these keys have) and you want to isolate them from a much more jumbled background, you do this:

Activate one of the rectangles and turn the camera so that the rectangle is perpendicular to the lines in the intended subject. The sensor will see those perpendicular lines better than it sees anything else and zero in on them.

It also helps if you do manually focus close to the actual subject,so that the system sees the lines in the subject clearly before it sees clear lines anywhere else.

[tkbslc]

manual focus can be tricky, but I usually do OK if I:

-make sure my diopter adjustment in the viewfinder is set correctly
-use reasonable DOF so there is a little margin for error
-focus bracket - take 3 shots - 1 where you think it is in focus and then 1 a bit on either side of that mark
-take your time
-use liveview if you got it.

Old cameras had focusing aids in the viewfinder so it was not as hard. New cameras at AF optimized.

[rdenney]

manual focus can be tricky, but I usually do OK if I:

-make sure my diopter adjustment in the viewfinder is set correctly
-use reasonable DOF so there is a little margin for error
-focus bracket - take 3 shots - 1 where you think it is in focus and then 1 a bit on either side of that mark
-take your time
-use liveview if you got it.

Old cameras had focusing aids in the viewfinder so it was not as hard. New cameras at AF optimized.

Old cameras (older than you are thinking) often had no focusing aids at all, and we still were able to focus them.

Live-view is great. None of my cameras does it. Stopping down a bit helps, too. Getting the finder diopter adjustment right is indeed critical. That gives you sharp finder markings against which to compare subject material.

The trick is to turn the focus control so that the image becomes noticeably blurry inside focus, and then turn it until it's equally blurry outside focus. Do it again, with smaller margins of blurriness. Then, split the difference.

I've been able to focus even an old 10D accurately using that method.

Rick "who uses the same method on view cameras with f/12 lenses and no fresnel, let alone a split image" Denney