Best results out of your AF system question

[goodguy]

What do you think is the best way to get sharpest picture possible ?

As an example I am shooting a portrait, does using the centre point which is a cross type AF point pointing at the eye of the person and then recomposing or should I use other AF points possibly non cross type point without the need to recompose ?

 

[beachrat]

Shouldn't a lot of that decision be based on aperture,lens focal length and distance to subject?

 

[sk66]

Shouldn't a lot of that decision be based on aperture,lens focal length and distance to subject?

In other words, DOF?
Focus-recompose should be avoided when working with a very shallow DOF.

Possibly "the best way" would be to focus in live view with the focus point selected/placed on the eye... but that's not terribly practical.

 

[julianliu]

I have the same question. I often use the non center point to focus on eyes but I do find I have some not so sharp pic in the end.

 

[Overread14 2]

Imagine the depth of field like a sheet of paper, set parallel to the front of the lens. When you set the focus you move that plane of focus back and forth and what the paper covers is what's in-focus and sharp.

Now as a result of this if you've a wide aperture, thus a small depth of field (thin paper) what happens when you recompose is you change the angle of the lens in relation to the subject. Now when that paper moves it can very easily end up not covering the original point of focus in the scene. As a result focus and recompose is not ideal unless you adjust focusing after recomposition or you're using a smaller aperture and only recomposing by a small amount (the original point of focus might not be at the point of most critical sharpness, but it will land within the depth of field and thus be sharp).

 

[71M]

As an example I am shooting a portrait, does using the centre point which is a cross type AF point pointing at the eye of the person and then recomposing

Usually, that's what I do - particularly for eyes/portrait; I think it's still a habit from using split-screens, before AF on the SLR was common.

 

[Derrel]

I usually use the 4-way controller and shift the active focus point to the area of the viewfinder screen image that is closest to my desired focusing point. So, if I am shooting a vertical portraits, I will therefore typically be using the outer edge of the focusing point pattern. Typical distance, 6 to 12 feet from the subject. If focusing and/or adequate depth of field is absolutely critical, it really helps to shoot at a smallish f/stop, like f/6.3 to f/8.

I seldom photograph close-range subjects at wide apertures like f/2.8...there's just not enough depth of field to render most of the frame in good focus. I'm also not a fan of the ears being way out of focus, so I typically don't really like to shoot with less than "half of a head's worth" of depth of field.

 

[beachrat]

Shouldn't a lot of that decision be based on aperture,lens focal length and distance to subject?

In other words, DOF?

:mrgreen: 'Zactly.

 

[goodguy]

I have the same question. I often use the non center point to focus on eyes but I do find I have some not so sharp pic in the end.

I see we have same problem

Imagine the depth of field like a sheet of paper, set parallel to the front of the lens. When you set the focus you move that plane of focus back and forth and what the paper covers is what's in-focus and sharp.

Now as a result of this if you've a wide aperture, thus a small depth of field (thin paper) what happens when you recompose is you change the angle of the lens in relation to the subject. Now when that paper moves it can very easily end up not covering the original point of focus in the scene. As a result focus and recompose is not ideal unless you adjust focusing after recomposition or you're using a smaller aperture and only recomposing by a small amount (the original point of focus might not be at the point of most critical sharpness, but it will land within the depth of field and thus be sharp).

I always play with my AF point so AF point lands exactly on subject eyes, this way I dont need to move camera but I find many times eyes still not 100% sharp so I thought maybe since centre point is always cross type maybe this will help get sharper results.

 

[KmH]

It depends on what AF system you are referring to.

Not all focus points are equal. Some are oriented to detect horizontally oriented lines of contrast, some are oriented to detect vertically oriented lines of contrast, and some are cross-type AF points that can detect both vertical and horizontal lines of contrast.

The number and orientation of the AF points in DSLRs varies. Some have none of the cross-type AF points and some have as many as 15 cross-type AF points. Some cross-type AF points have enhanced performance for use in low light.

 

[goodguy]

I usually use the 4-way controller and shift the active focus point to the area of the viewfinder screen image that is closest to my desired focusing point. So, if I am shooting a vertical portraits, I will therefore typically be using the outer edge of the focusing point pattern. Typical distance, 6 to 12 feet from the subject. If focusing and/or adequate depth of field is absolutely critical, it really helps to shoot at a smallish f/stop, like f/6.3 to f/8.

I seldom photograph close-range subjects at wide apertures like f/2.8...there's just not enough depth of field to render most of the frame in good focus. I'm also not a fan of the ears being way out of focus, so I typically don't really like to shoot with less than "half of a head's worth" of depth of field.

I am forced most times to shoot around f2.8 simply because of lighting conditions and flash isn't always handy.

 

[beachrat]

Probably better off stopping down a bit,and using a tripod.Or monopod.
Or get some more distance and crop.
Your initial question was,"What do you think is the best way to get sharpest picture possible ?"
Shooting at 2.8 probably doesn't help.

 

[hirejn]

The bottom line is when I need it correct, I don't mess around and I dial in an exact focus point, single shot servo, without recomposing. At greater distances and small apertures there's less of a need to dial in an exact point and you can recompose. For 1/2 length or closer portraits, there's no question I go to custom point, single shot, and for those portraits I'm generally at f/4 or wider anyway, unless I'm in a studio.