srt101fan

I use back-button focus. I usually move the camera to position the focus point over the area I want to focus on and then move the camera to recompose.

I remember reading somewhere on UHH that you shouldn't do that; instead, you should reposition the focus point in the camera using the controls provided for that. This was touched on again recently in a UHH post but no rationale was given.

What is the reason for preferring to move the focus point in the camera vs moving the camera to focus and then recomposing?

Thank you.

BebuLamar

For sure it's easier to move the camera and recompose but doing so does introduce some inaccuracy to focusing. When you move the camera the distance is slightly different and more so at close distance than at far distance. However, with a rangefinder camera (or an SLR using the split image) people have been moving the camera to focus and recompose in ages but nobody said anything until AF was introduced.

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Curvature of field is the main reason. I think you know what that is. If not just google. It’s not an obscure topic. A lesser but real problem at rather near distance is that when you re-aim you tilt the focus plane differently than when you focused. The relocated plane might not intersect the detail you focused on. Add both of those minor problems together and at wider apertures your focus may be off by enough to be visible.

Wingpilot Loc: Wasilla. Ak

I would say that if you are shooting a distant object, say a landscape type of scene and you wanted to emphasize a certain part of the scene, focusing on that object then recomposing is not a problem. However, if you are shooting something close, especially something with a lot of detail, say a macro or close up, or you need a bird’s eye in sharp focus, then moving the focus point is a much better choice.

ORpilot Loc: Prineville, Or

What came first the chicken or the egg. It really doesn't matter which way you do it. What matters is; do you get the final image you want? If so then why change. Most old school (manual camera film photographers) do the focus on the intended subject and then recompose the camera for the shot. I have started doing both. It just depends on the subject matter. If you have follow focus ability in your camera , you are essentially focusing and then recomposing the camera. I shoot mostly landscapes so I am using DOF and moving the focus point all over the place as well as recomposing the shot. It all comes down to getting the shot you want. So, whatever works for you is the right way to do it. Happy shooting

btbg

One of the reasons no one has touched on yet is if your focal point is intended to be on a moving object. It is much more efficient to move the focus point to the object than to focus on it and recompose. By the time that is accomplished the object has moved again.

Examples include sports photography, birds in flight, galloping horses, moving cars or trains, etc...

ORpilot Loc: Prineville, Or

My Alaskan friend makes a good point. I, like many when shooting macro will go into manual focus and move the focus point via subject to lens distance for that fine critical focus. That is what a focus rail is designed for. But as I previously stated, what ever works for you is best for you.

bleirer

If you really want the eye of the eagle to be the tack sharpiest thing in the picture, put the focus point right there. If you focus on a subject in the center then move the camera left or right or up or down, the plane of focus moves a little behind the subject.Could make a difference in some situations, depending.

jackpinoh Loc: Kettering, OH 45419

This is the correct answer. The sensor is a 2-dimensional plane. So is the plane of focus. As you turn the camera after locking in the focus, the plane of focus rotates as you turn. So any objects that were in focus are now out of focus, because the focal plane is now behind your subject. How much out of focus depends on the depth of field--determined by the lens focal length and aperture and your distance to the object on which you focused.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

On most cameras, the center focus point is most accurate - being a "cross-type" focus point, capable of focusing on both horizontal and vertical line pairs - this is the most versatile and fastest point on the focus screen in most circumstances. Cameras have other cross type focus points, and some that are best for focusing on horizontal line pairs and others on vertical line pairs.

In some circumstances shifting the focus point to one that is not dead center isn't a bad thing. Like when you are shooting portraits in portrait orientation. Better results will be achieved if you can shift the primary focus point to a location more or less where the eyes would be. Better than focusing by moving the camera to focus with the center point and recomposing.

I am not sure that field curvature is an issue - if you have something that is off-center that needs to be in focus, moving the focus point to that location will still ensure that the target will be in focus - but other parts of the image may not be.

There is another concern - focus shift with change in aperture. AF systems focus with the lens wide open.

https://photographylife.com/what-is-focus-shift

As the article in the link states, this only applies to PDAF, or phase detect AF systems. When using live view, most cameras use CDAF, or contrast detect AF.

DWU2 Loc: Phoenix Arizona area

I prefer your method. Let's say you're photographing a bird. If you have to screw around with controls to change the focus point, by the time you finish, that bird will have flown.

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At landscape distances the topic of this thread is a moot question. Won’t matter in the least how you approach focus and composition. At tripod apertures even curvature of field has no effect.

a6k Loc: Detroit & Sanibel

1. If you are using the EVF it seems to me that moving the focus point is harder.
2. If you are lucky enough to have live view and focus peaking you can see the focus points all over the frame.

FWIW, I use the half-push method to hold the focus point in AF mode while slightly re-framing. This is best for me when shooting a reasonably static bird but still want correct composition. Just one way that works for me, not the only way by any means.

Longshadow Loc: Audubon, PA, United States

The plane of focus (vertical) shifts (forward or backward) depending on if you lower or raise the camera after focusing on something. More evident with a narrower depth of field.
Knowing this effect, one can focus a bit in front of or behind the intended focus point, as dictated by the change in camera angle if the depth of field is not large enough to cover the difference. (In front of the intended focus point if the camera gets pointed downward, behind it if the camera gets pointed upward for the change in composition.)

CHG_CANON Loc: the Windy City

Develop the finger feel and practice with your camera to able to move the AF point without lowering the camera from your eye. When you become one with your camera, the magic begins.

Alternatively, prepare for the composition. Position the AF point / group / zone within the frame before the bird / subject appears. Position yourself / camera so the AF point overlays the subject, then shoot.