brainiac wrote:
Either way, using the centre to focus and then swinging the camera around to recompose will give you incorrect focus, even with a lens that has no field curvature at all. The wider the lens, the greater the angle of swing (recomposition), and therefore the greater the error. With wide angles, if you are interested in corner sharpness or off-centre subjects, focus recompose sucks. Smaller apertures hide the error, but it is still an error.
I dont quite agree, a lens with a strong curvature of field is more likely to give you correct focus distance with focus-recompose, Think about a fisheye.
On the other hand the same lens which is good at one thing will be poor in another situation, like Landscape/outdoor architecture where it would be nice to have a lens without any curvature of field.
Focus-recompose induces a slight back focus with a perfect lens.
Since you need to front focus with a lens suffering from (or blessed with) field curvature, it makes things much worse.
Andi Dietrich wrote:
I dont quite agree, a lens with a strong curvature of field is more likely to give you correct focus distance with focus-recompose, Think about a fisheye.
On the other hand the same lens which is good at one thing will be poor in another situation, like Landscape/outdoor architecture where it would be nice to have a lens without any curvature of field.
brainiac wrote:
With wide angles, if you are interested in corner sharpness or off-centre subjects, focus recompose sucks. Smaller apertures hide the error, but it is still an error.
Totally agreed. Focus-recompose brings only trouble due to field curvature.
One has to compose first, then focus visually (or AF using a peripheral point but that is not always possible because AF points are too centered on FF bodies).
Focusing this way, it is not unusual to find that a peripheral object which is at 2 meters difference might require a focusing distance of 1.5 meters or less depending on the strength of the curvature and how far the object is from the center.
For snapshots and reportage, I try to focus-recompose with the closest AF point to the subject. Not perfect but fast.
For landscapes at infinity, it is best to focus visually at the corners and try to find a compromise with the centre focus (which should be at infinity) and cover the difference with a small f/stop.
brainiac wrote:
Not really. When the lens is focussed closer, it will have less effective depth of field. Either way, using the centre to focus and then swinging the camera around to recompose will give you incorrect focus, even with a lens that has no field curvature at all. The wider the lens, the greater the angle of swing (recomposition), and therefore the greater the error. With wide angles, if you are interested in corner sharpness or off-centre subjects, focus recompose sucks. Smaller apertures hide the error, but it is still an error.
I don't say that focus recompose does not suck, I just say that the introduced error depends on the object distance. For a faraway scenery, there will be no error as everything is within the depth of field, before or after recomposition. At close(r) focus errors occur, hence the dependence on object distance.
There is an FM member that posted some Nikkor 14~24 shots here with Hubsand's adapter, I think he is in the UK. He had some rocks by the sea in the extreme foreground, with the sea in the horizon, and intense colored cloudy skies. He has the W/A focus procedure nailed.
I agree with Edward's technique too. For a landscape I would use f8 and then blend multiple exposures focussed at different parts of the frame using liveview. As Edward says, the lens barrel marking which gives best sharpness in the corner can be very surprising. It's yet another killer app for liveview that it takes all guesswork out of this process. Sometimes that's the only way to get 21+ megapixels of sharpness across the whole scene, even with very excellent lenses.
jjlphoto wrote:
There is an FM member that posted some Nikkor 14~24 shots here with Hubsand's adapter, I think he is in the UK. He had some rocks by the sea in the extreme foreground, with the sea in the horizon, and intense colored cloudy skies. He has the W/A focus procedure nailed.
I also like the f8 multiple exposure image blend with my 14-24G using liveview if there is alot of fine detail in foreground and background that I want sharp. The other way is to try to do it with a diffraction affected f11 or f16 aperture which you maybe able to get away with scenes with not alot of fine detail like ocean water and polished sea rocks.
brainiac wrote:
I agree with Edward's technique too. For a landscape I would use f8 and then blend multiple exposures focussed at different parts of the frame using liveview. As Edward says, the lens barrel marking which gives best sharpness in the corner can be very surprising. It's yet another killer app for liveview that it takes all guesswork out of this process. Sometimes that's the only way to get 21+ megapixels of sharpness across the whole scene, even with very excellent lenses.
edwardkaraa wrote:
Focus-recompose induces a slight back focus with a perfect lens.
in theory yes, but then a photographer does not stand on a turning wheel while he is focus-recomposing and at the end it is very situational as toothywalker said.
Whenever I use my WA zoom to do this, focus is pretty much ok while my success rate with the ZF 18, which has a rather plane field of focus, is much lower. Maybe it is because the AF is more capable to focus than I am though.
