Focus Accuracy

[pfogle]

My 2c - the argument that the plane of focus will be further from the subject when you turn to place the subject at the edge of the frame is surely correct. And, though a slightly spherical focus is not uncommon in wide-aperture lenses, it's always regarded as a fault and never designed in - ideally you want to be able to photograph a flat wall and have all the bricks (or whatever) in focus. In practice, the plane of focus often becomes spherical as you focus closer, due to lens abberations.

That said: if you turn by more than a few degrees, you must be shooting on a wide-angle, so you have enough DOF to cover the shift, and if you are using a longer lens, the amount of shift is too small to notice.

 

[madmaxmedia]

My 2c - the argument that the plane of focus will be further from the subject when you turn to place the subject at the edge of the frame is surely correct. And, though a slightly spherical focus is not uncommon in wide-aperture lenses, it's always regarded as a fault and never designed in - ideally you want to be able to photograph a flat wall and have all the bricks (or whatever) in focus. In practice, the plane of focus often becomes spherical as you focus closer, due to lens abberations.

That said: if you turn by more than a few degrees, you must be shooting on a wide-angle, so you have enough DOF to cover the shift, and if you are using a longer lens, the amount of shift is too small to notice.

This seems like the best summary of the real-world effect. Nice thread, never realized re-composing would have that effect!

Of course, the ultimate solution is to not rotate the camera, but step sideways so that your subject is still in the focal plane!

(just kidding. I mean it would work, but only if you're on a dolly whose tracks have been carefully aligned with your focal plane...)

 

[roblumba]

Back to Square One

Back to Square One

So now we are full circle back to my original understanding. The focal plane is flat (i.e. the brick wall), and your subject will no longer be in the focal plane when you rotate.

I know it's said to be a moot point with wide angle, but when you are focusing in low light with a fast lens at f1.4, you can easily see that the plane of focus has shifted. Sure, perhaps you can say it's a more impressionistic style of photography, but my eyes are used to seeing things in focus. And when I can clearly see the ears are in focus while the face is not, the impressionistic style exuse just looks silly.

 

[roblumba]

Awareness

Awareness

I suppose it's a limitation I must be aware of in certain circumstances. I see a number of ways of working within this limitation.

1. Don't focus recompose.

2. Focus bracketing.

3. Guestimate the amount of focus adjustment needed.

4. Use a smaller aperature.

5. Choose an angle and distance from the subject that increases the DOF and doesn't require a dramatic recomposition shift.

6. Frame the scene with your focal plan in mind and imagine the focal plane in your scene. (3D awareness). Focus on an object in the center of the frame but in the same focal plane as your subject(s).

I think the #5 and #6 options are probably the smartest since 1-4 can lead to dissapointment.