Focus/Reframe

[Alexs]

Hi guys/girls,

You have been a tremendous help to me and let me just say I appreciate all your critique so far...

For focusing I use the method of using 1 AF point (centre one) to focus on the subject, then reframe. I also use spot metering in many cases, and this turns out to be convenient since the centre spot is used for focus/metering.

However, I have found that sometimes the subject is a little soft. It usually varies with the available light (i.e. the more light I have, the better the autofocus works...duh), and in this case, the subject could have moved between when I focused and when I actually took the shot (I focused on the face/eyes).

Basically I want to know if there are any tips for keeping a tricky subject (i.e. dancer/musician) in focus using this technique (other than being faster or increasing the DOF). Any other critique on the shot would also be welcome...thanks in advance and sorry for the long writeup.



Camera Model: Canon 500D
Lens Model: EF50mm f/1.8 II
Shutter Speed: 1/400
Aperture Value: 1.8
ISO Speed: 100

[PeterArboinePhotography]

Hi Alexs, I would look at bumping up your iso a little, this helps you get rid of the motion blur a little...

[Pitrih]

hi!

you have to increase DOF, f1.8 is too shallow for portratits...or for anything else, try using at least f2.8, i found that f4.5 works best for portraits (i have the same lens).

and bump up your ISO as suggested.

[sk66]

While both previous suggestions will reduce the chance for lack of focus, I don't see anything "wrong" with your settings.
I'm not certain about Canon, but you should be able to select which point is used for focus. This will remove the requirement to reframe and allow quicker focus/release times. With my Nikon I can assign the focus and metering function to separate buttons allowing me to spot meter with one and focus with another. Check your manual.

[Vagebond]

Maybe it's me, but that black thing standing to the right looks to me like it's in reasonably sharp focus. It also looks like it's at least a bit closer to the camera than your subject.
You don't have much wiggle room with depth of field at F1.8. Are you sure that either or both subject and camera didn't back off a bit when you recomposed and completed the shot?

[sybren]

Focus & reframe only works when your subject stays withing the DOF. At f/1.8 you'll rotate your subject right out of it. Your lenses are built such that they have a focus plane, and that plane rotates along with your sensor. If you focus on your subject's eye, then rotate the camera to the right, the focus plane will lie behind his eye. With shallow DOFs it's often better to pick the correct focus point, and use servo AF to keep focusing until you take the shot.

[sybren]

Originally Posted by Pitrih

you have to increase DOF, f1.8 is too shallow for portratits...

That's a strange thing to say. It works fine for me, it just takes getting used to in order to use it effectively. Canon's 85mm f/1.2 is a very popular portrait lens. If what you're saying is true, people wouldn't prefer it over the f/1.8...

[Alexs]

Thanks for the great tips, I understand that the subject of focus has to be within the DOF etc but the tip to use the correct focus point is something that I will employ in the future. It adds a little setup time before starting to take shots I guess?

Also, not sure how good the AF Servo on the 500D is but I shall be giving it a workout after I figure it out. Thanks for the tip.

Increasing the ISO would allow me to decrease shutter speed, but I think 1/400 should be fast enough for a fairly static subject (i.e. non sports)? Am I wrong in assuming that?

Not gonna get into the aperture argument...I'll leave that to the more experienced posters!

[sk66]

Increasing the ISO would also increase the shutter speed. Higher ISO= more light sensitivity, more light sensitivity=less exposure time. But yes, 1/400 should be more than fast enough for a 50mm and slow subjects.

[Alexs]

oops, i meant decrease the time the shutter is open....spot the beginner!