Which focus points do you use? (Or, do you focus and recompose?)

[jonathanj]

This is a question which has vaguely puzzled me for a while. I have a Samsung NX20, which has (so I understand) fairly ordinary AF performance for a mirrorless camera. I very very rarely shoot sports or fast moving objects, so I'm perfectly happy with it, but it seems like the way I use autofocus doesn't match anyone else's habits, and I'm wondering if I'm missing something...

With every digital camera I've owned, I've always used the center autofocus only, and recomposed as necessary after focusing (Or, with moving subjects, cropped to frame afterwards, as I rarely make prints and almost never at large sizes, so crops generally have all the resolution I need.)

Based on an extremely un-scientific monitoring of friends, family, people I ask to take photos of me, and tourists I see around the city, it seems pretty much everyone leaves the autofocus in full auto, points the camera in vague direction of the subject, and hopes it magically autofocusses on what they want. (This behavior seen even with users of mid range DSLRs with $1,000 lenses) When I've tried it this way, the results have been pretty hit and miss.

I also notice the criticism of the Canon 6D about the AF points. I'm not in the market for a full frame DSLR, but if I were, the 6D's superb centre point AF sounds ideal - I don't really care about 39 AF points, as it seems faster to focus and recompose than to mess around selecting the right one of those 39...

So am I missing something or just stuck in a timewarp? Are high end cameras really that telepathic nowadays? Interested to hear people's thoughts!

 

[Hank3152]

Focus locking and recomposing doesn't always get the subject sharp if the subject is laterally further away from the lens after recomposing, especially when using large apertures. Here's a better explanation......
http://photo.stackexchange.com/questions/12150/why-would-i-want-to-select-an-autofocus-point


On modern DSLRs it's relatively quick to press one easily accessible button and toggle to the desired focus point and shoot.

 

[BertIverson]

[No message]

 

[mosswings]

Evaluative metering systems (Nikon Matrix Metering, for example) base their exposure calculations on what's under the focus point. When you focus and recompose, you change the lighting balance that the meter sees - cameras are generally set up to lock only focus on the half-press but continue metering until the shutter is fully depressed.

For close camera-subject distances or when shooting with very small depth of field (fast lens), focus-and-recompose can cause path length differences that induce focus error.

I've always moved my focus point around when framing for this very reason. With higher density AF systems this may become less of a problem in terms of getting the focus point where you want it.

 

[Hank3152]

With some lenses (mostly fast wide-angles) there's a possible problem from focusing and then re-composing: as you re-compose, what you originally focused on will no longer be on the plane of focus.

With longer lenses, this is rarely much of a problem, if you're shooting with something like a 30/1.4 on full frame, your subject could be quite a ways out of focus by the time you compose the picture.












This makes the biggest difference when there's a fairly large angle between where you focused and where you shoot. The slower the lens, the more depth of field you have to cover the discrepancy.

--
Regards,
Hank
http://www.dpreview.com/galleries/638311471/photos/17792/night-launch

 

[Martin.au]

jonathanj wrote:

This is a question which has vaguely puzzled me for a while. I have a Samsung NX20, which has (so I understand) fairly ordinary AF performance for a mirrorless camera. I very very rarely shoot sports or fast moving objects, so I'm perfectly happy with it, but it seems like the way I use autofocus doesn't match anyone else's habits, and I'm wondering if I'm missing something...

With every digital camera I've owned, I've always used the center autofocus only, and recomposed as necessary after focusing (Or, with moving subjects, cropped to frame afterwards, as I rarely make prints and almost never at large sizes, so crops generally have all the resolution I need.)

Based on an extremely un-scientific monitoring of friends, family, people I ask to take photos of me, and tourists I see around the city, it seems pretty much everyone leaves the autofocus in full auto, points the camera in vague direction of the subject, and hopes it magically autofocusses on what they want. (This behavior seen even with users of mid range DSLRs with $1,000 lenses) When I've tried it this way, the results have been pretty hit and miss.

I also notice the criticism of the Canon 6D about the AF points. I'm not in the market for a full frame DSLR, but if I were, the 6D's superb centre point AF sounds ideal - I don't really care about 39 AF points, as it seems faster to focus and recompose than to mess around selecting the right one of those 39...

So am I missing something or just stuck in a timewarp? Are high end cameras really that telepathic nowadays? Interested to hear people's thoughts!

For general photography I shoot centre and recompose.

For macros and other close range stuff I move the focal point to wherever I want to focus on.

 

[jonathanj]

Hmmm - thanks for that explanation, that makes a lot of sense. I guess it's something I haven't noticed as I rarely shoot nearby things with the lens wide open

...actually, now I come to think about it, when I do shoot portraits or "macro" shots, I generally stick to the center and crop, as most of my (cheaper) lenses are noticeably less sharp at the edge anyway, so maybe that's why I've not noticed this. But definitely something to keep in mind if I ever buy a true macro lens!

I think I'll try and test this out when I get a chance, to see how noticeable the effect is. Any rough idea what sort of distance this becomes significant (with, let's say, f4-5.6 on an APS-C sensor)?

 

[ShotFromTheSidewalk]

when doing landscapes, i'll focus into the scene and recompose. i'm at a higher f-stop in this case (f8 or f11).

for fast movers (bikes and motorized), i'll just focus and crop later. sometimes, i'll pre-focus at a particular place (let's say it's a road for bikes or race-track for cars)


people shots i'll generally just focus and crop later for composition.

close-up, tripod mounted, i'll use live-view and with AF or MF move the focus point to my subject for the composition i like.

i only use the center AF point (D600).

 

[Hank3152]

jonathanj wrote:

I think I'll try and test this out when I get a chance, to see how noticeable the effect is. Any rough idea what sort of distance this becomes significant (with, let's say, f4-5.6 on an APS-C sensor)?

Not a clue due to the many variables......

 

[Martin.au]

Hank3152 wrote:

jonathanj wrote:

I think I'll try and test this out when I get a chance, to see how noticeable the effect is. Any rough idea what sort of distance this becomes significant (with, let's say, f4-5.6 on an APS-C sensor)?

Not a clue due to the many variables......

 

[AllMankind]

Mjankor wrote:


Relates to angle of view too.

In my experience, for macro it's critical. For everything else, it's a fairly minimal issue.

Exactly.

I am shooting with a Nikon D800E and all I ever use is the center AF point.

Focus and recompose is far faster than futzing with AF points while trying to capture an image, especially is the subject is in motion.

I have zero issues with OOF images.

I don't shoot marcos, but if I did, I would not use focus and recompose. It is only at quite short distances that focus errors are an issue. Anything beyond about 1 meter, especially if NOT shooting wide open, is NOT an issue.

 

[AllMankind]

mosswings wrote:

Evaluative metering systems (Nikon Matrix Metering, for example) base their exposure calculations on what's under the focus point. When you focus and recompose, you change the lighting balance that the meter sees - cameras are generally set up to lock only focus on the half-press but continue metering until the shutter is fully depressed.

For close camera-subject distances or when shooting with very small depth of field (fast lens), focus-and-recompose can cause path length differences that induce focus error.

I've always moved my focus point around when framing for this very reason. With higher density AF systems this may become less of a problem in terms of getting the focus point where you want it.

Youu can separate the AF function from the exposure function. Once you do that, this is not an issue.

 

[mosswings]

AllMankind wrote:

mosswings wrote:

Evaluative metering systems (Nikon Matrix Metering, for example) base their exposure calculations on what's under the focus point. When you focus and recompose, you change the lighting balance that the meter sees - cameras are generally set up to lock only focus on the half-press but continue metering until the shutter is fully depressed.

For close camera-subject distances or when shooting with very small depth of field (fast lens), focus-and-recompose can cause path length differences that induce focus error.

I've always moved my focus point around when framing for this very reason. With higher density AF systems this may become less of a problem in terms of getting the focus point where you want it.

Youu can separate the AF function from the exposure function. Once you do that, this is not an issue.

Can you demonstrate?

Evaluative metering's focal point bias doesn't change if you separate the AE and AF lock functions. If you decouple AE from the shutter, then focus using only the center focus point, then lock AE, the exposure selected will be for that composition. It won't be correct for the final composition. If you don't change the default AF/AE operation (which is usually to keep AE active until time of capture), the camera will base its final exposure on what's under the iniitial focus point, which is now moved off of your subject. Either way, it's not strictly correct.

Under most circumstances this doesn't make much difference. But under some circumstances - like, for example, a pianist in front of a black piano, focusing first on the pianist and then recomposing can wind up overexposing the pianist as the meter tries to deal with the large expanse of black that's just entered the scene.

If I'm confused, I'd appreciate being set straight.

 

[Gato Amarillo]

I shift the focus point as needed or for people use face detect. With the latest mirrorless cameras from Panasonic (which I currently use) the focus point can be anywhere in the image and easily be set with the touch screen.


IMO, focus-and-recompose is not idea for composition or focus accuracy.

Gato

"We paint with our brain, not with our hands" -- Michelangelo

Portrait, figure and fantasy photography at Silver Mirage Gallery:
silvermirage.com

 

[BertIverson]

AllMankind wrote:

I am shooting with a Nikon D800E and all I ever use is the center AF point.

Focus and recompose is far faster than futzing with AF points while trying to capture an image, especially is the subject is in motion.

Exactly

I have zero issues with OOF images.

Nor me with either camera I own.

I don't shoot marcos, but if I did, I would not use focus and recompose.

Exactly. Why would one have to recompose a macro? Use center focus on the item or use manual focus

It is only at quite short distances that focus errors are an issue. Anything beyond about 1 meter, especially if NOT shooting wide open, is NOT an issue.

Exactly


Certainly, if one is using a tripod on a static subject and has the time to compose and then choose the AF sensor, go for it - as it gives the mathematically correct AF.

Bert

 

[BertIverson]

Hank3152,

Sorry my subject line was incorrect. It should have said "I Always focus and recompose" I did not mean to imply that everyone should always focus and recompose. Your explanation of the trigonometry is excellent.

I'll do better the next time :-(



Bert

 

[hedwards]

I don't know about Nikon, but I know that my Canon heavily weights the final exposure to whatever is under the AF point I'm using.

I suspect that Nikon and the other manufacturers do that as well.

 

[Hank3152]

AllMankind wrote:

Exactly.

I am shooting with a Nikon D800E and all I ever use is the center AF point.

I use center point most of the time, and all the time for sports/action. But sometimes there is an occasional need for a different AF point when you need dead on sharp focus when your subject is off center and stationary when time isn't a factor.

Focus and recompose is far faster than futzing with AF points while trying to capture an image,

Not sure about Nikon but it takes me no time at all to select a desired AF point on a 1DmkIV.....2-3 seconds?

 

[jonathanj]

Interesting, not sure what cameras everyone is using, but on mine there is an AEL button that can be set to: AE lock, AF lock, AF+AE lock, or AE hold. (I use the last one, for ensuring every shot in a stitched panorama is equally exposed.)

When I focus and recompose normally, I do so by half-pressing the shutter and holding it half-pressed while I recompose. This is very quick, but as pointed out means the exposure is locked to the initial composition. I hadn't really paid much attention to this before...

I tested and if I set the AEL button to AF lock, then half press the shutter on the subject, press AF lock, recompose, then the exposure correctly changes. This is a few more steps, but still a bit faster than moving the AF point (still less than a second, I think).

 

[Mark S Abeln]

If I am shooting landscapes, I use the center focus point, since I mainly focus on something far away and one focus point is usually as good as another.

If I am in a big hurry, need to shoot quickly, and the subject is moving, I select all the focus points and let the camera decide. For example, I was recently shooting a parade, and I didn’t want to think much about my focus point. I rarely use some of the more advanced focusing modes which attempt to select a moving subject and keep focus on it — were I to do lots of sports and such, this might be useful.

I’ll use the center point and recompose if my camera doesn’t have to move so much as to change exposure.

If I am taking my time, the subject is static, and I want best quality, I’ll select the focus point manually. I was doing a portrait session the other day, and I adjusted the focus point to be on my subject’s closest eye. This is what I also do if I am doing macro photography, where focus is critical.