Manual Focus (Portraits)

I have an XSI, and usually use the 50mm f/1.8 mkii lens for portraits. One thing that's been bothering me lately is that I always have to use manual focus when doing portraits, which really turns out to be hit and miss. Autofocus just never gives me sharp photos. Is it because of the lens that I have to use manual focus? I know that using an aperture like 1.8 is going to give me a shallow DOF and therefore make it harder to focus on a precise area, but I have to manual focus even when the aperture is set to f/5.6 to get a sharp photo. Is this normal?

http://www.flickr.com/photos/48939759@N07/4907065533/


Above is a link to a picture I particularly like; it was just a fluke that I focused well.

Our focuses, on the next rebel up, the T1i. It's hard to tell at f/1.8 because of potential camera and subject movement, and softness wide open, but at f/2.2-f/2.5 or so, it's great. Are you choosing an appropriate focus point, or attempting to focus and recompose? Recomposing doesn't work well with a thin DOF.

I don't recompose, I just stay in one place and try to get the same picture but focused differently until it's sharp (at the eyes).

This is a crop from the first 50mm shot I found while digging around. It's a 100% crop taken at f/3.2.


http://farm5.static.flickr.com/4118/...f7704167_b.jpg


I'm having a hard time finding a shot wider than 3.2 that isn't hampered by the fact that it was really dark and we used ISO-3200 as well...

My 50mm f/1.8 front-focused by a mile. If you get a body with microadjustment that might solve the problem.

Ouch, manual focussing with a 50mm 1.8 [^o)]

Quote:

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Originally Posted by BogdanD

I have to manual focus even when the aperture is set to f/5.6 to get a sharp photo. Is this normal?

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No it is not normal. While the auto-focus motor isn't the fastest available, you should have good autofocus results. Or your lens might suffer from front- or backfocus. In other words, it always focus just in front or to the back of the area you'd like it to focus on.


At f1.8 your lens is not the sharpest, so it's hard to judge if your lens focusses correctly at f1.8. However you could do the testing at f2.8 or so where the lens should be pretty sharp.


If your lens exhibits focussing-errors there are two things you can do. Send it back to Canon to recalibrate (if it's worth it) or buy a camera with micro-adjustment so you can compensate for the front- or backfocus.


Hope that helps,


Jan


Ps: I like the picture [Y][:D]

I think it's a good idea to use a medium format camera for people
pictures. I use a Pentax 645 with a 150 lens often. I do 100% black
and white because I do it myself. I like having proof sheets that are
viewable and 15 shots is economical but still greatly superior to 35 mm
for portraits.

Thanks for the tips! I don't think I'll send it back to Canon because they'll probably charge me more than the thing is worth. [:P]

If you don't try, you will never know [;)]


I hope you can figure something out, good luck.


Jan

My copy of the 50mm f/1.8 II front focuses a lot as well. It was pretty much unusable on my 40D but works very well on the 5D2 with a significant microadjustment (+14 from memory).


You're probably right in that Canon might charge you more than the lens is worth to calibrate it but you might consider sending in your whole kit and getting everything calibrated together. I dare say you'll find things less of a chore once it's all working as it should.


Ben