What's the need for so many focal points? Isn't just one enough?

[cgipson1]

The horizontal/vertical and cross type are different kinds of sensor - they will all focus on the same things, however the cross type are the most accurate of the three types and the most reliable.

In cameras with weaker AF systems, such as the rebel series cameras and the 5D and 5DMII the cross type middle sensor is the most powerful and often the only cross type in the setup. As such many people will favour it and then either compose with cropping in mind or will recompose - adjust the focus manually and then shoot.

Higher end AF systems such as the one in the 7D or 5DMIII have many more cross type AF points on offer and thus the viability of those external points is increased.

So, does it mean I'm doing the right thing by slecting the central AF point for locking focus and then re-composing for taking the shot (as I have a 550D)?

Depends.. do you often miss focus due to recomposing?

 

[raaskohx10]

The horizontal/vertical and cross type are different kinds of sensor - they will all focus on the same things, however the cross type are the most accurate of the three types and the most reliable.

In cameras with weaker AF systems, such as the rebel series cameras and the 5D and 5DMII the cross type middle sensor is the most powerful and often the only cross type in the setup. As such many people will favour it and then either compose with cropping in mind or will recompose - adjust the focus manually and then shoot.

Higher end AF systems such as the one in the 7D or 5DMIII have many more cross type AF points on offer and thus the viability of those external points is increased.

So, does it mean I'm doing the right thing by slecting the central AF point for locking focus and then re-composing for taking the shot (as I have a 550D)?

Depends.. do you often miss focus due to recomposing?

Sometimes while shooting landscape I feel pic comes out little soft. But over all I'm quite satisfied with the way the AF system of 550D works. Softness could be due to several other reasons too (camera shake, using image stabilizaton on tripod, lens quality, aperture settings, etc) but the debate going on for 5d Mark iii compelled me to try to understand the selection of AF points on DSLRs.

 

[table1349]

I don't know whether or not this question has been asked before. Just wondering why do modern DSLRs have so many focal points (my 550D has 9). I use the one at the centre, aim at my subject, lock the focus, recompose (if needed), and shoot. Simple. Any idea why camera manufactureres give so many focal points? Just to save our time from re-composing after locking focus? This question has come to my mind after reading complaints from 5d mark III users who say their pictures are not coming sharp (and they later find out that it was due to automatic selection of focal points by the camera). How do you guys shoot? Select the middle focal point (as it focusses both vertically and horizontally) or let the camera decide which one to choose?

Why the need for so many different lenses? Why the need for so many different camera's? Isn't one enough? Focal points are just a tool. Like with any tool there are proper ways to use it that have to be learned. As for letting the camera decide, you might as well let your blender or microwave decide which focal point to use. I have 61 focal points to choose from on my 1Dx. I select the one that lands on the one element of the photo that I want exactly in focus.

 

[o hey tyler]

Recomposing can fail - in fact many times it will fail. *

Using automatic point selection can fail, and often times it will fail. *

*if you don't know what you're doing.

I focus and recompose 100% of my shots and have not had more than a few unusable photos out of thousands due to a focus plan shift.

 

[enzodm]

Recomposing can fail - in fact many times it will fail. *

Using automatic point selection can fail, and often times it will fail. *

*if you don't know what you're doing.

I focus and recompose 100% of my shots and have not had more than a few unusable photos out of thousands due to a focus plan shift.

If I interpret correctly what Overread wanted to say, is that it might be better to use the focus point closer to the subject in the final composition, instead of using always the central one. No automatic selection, but just manual selection of the right one.
I typically use the central one but because often I'm lazy - when I think at what I'm doing (and I have time to decide), I try to choose one of the other points depending on composition. There is always the need for some recomposition, but much less.

 

[o hey tyler]

If I interpret correctly what Overread wanted to say, is that it might be better to use the focus point closer to the subject in the final composition, instead of using always the central one. No automatic selection, but just manual selection of the right one.
I typically use the central one but because often I'm lazy - when I think at what I'm doing (and I have time to decide), I try to choose one of the other points depending on composition. There is always the need for some recomposition, but much less.

I place as much faith in outlying focus points to achieve proper focus quickly and accurately as I trust Joaquin Phoenix to make a good movie.

 

[Benco]

If I interpret correctly what Overread wanted to say, is that it might be better to use the focus point closer to the subject in the final composition, instead of using always the central one. No automatic selection, but just manual selection of the right one.
I typically use the central one but because often I'm lazy - when I think at what I'm doing (and I have time to decide), I try to choose one of the other points depending on composition. There is always the need for some recomposition, but much less.

I place as much faith in outlying focus points to achieve proper focus quickly and accurately as I trust Joaquin Phoenix to make a good movie.

So you do trust your outlying focus points to achieve proper focus.

 

[o hey tyler]

So you do trust your outlying focus points to achieve proper focus.

Yeah, uh. No. With the exception of The Master.

 

[Patriot]

.............there are no built in manual focusing aids............

Both my D7000 and D600 have a rangefinder focus aid built into the VF. It will indicate which way to rotate the focus ring of the lens and then indicate when focus is achieved.

What is this magic you speak of!?

 

[amolitor]

There is a geometrical argument that focusing with the central point, and then recomposing results in a plane of focus that isn't quite where you want it. It's abolutely true that the plane of focus is now somewhere different.

There are even extreme cases where the difference is enough to matter. If you're swinging the camera through less than about 10 degrees in the "recompose" step, the differences are pretty negligible, though. Under 10 degrees the focal plane moves by less than 1.5% of the distance to the subject, which is probably less than other errors in play here.

NOTE: Over 10 degrees and the wheels fall off pretty fast. At 20 degrees, it's more like 6% and at 30 degrees it's more than 13%. At this point you're working with wide angle lenses and DoF is pretty deep, but still.

I use alternate focus points when I am tripod mounted, and recomposing more than slightly is a pain in the butt. And, heck, at other times too. Why not? They're there.

Center focus and recompose has worked just fine for a long long long time.

 

[EIngerson]

I very seldom use center focus then recompose. I frame the shot and select the focus point I want to use. The 5D3 doesn't seem to miss.

 

[greybeard33 5]

It helps when you have a really fast moving object to focus on like a flying bee etc. That is the only time I use more than 1 focus point.

 

[raaskohx10]

It helps when you have a really fast moving object to focus on like a flying bee etc. That is the only time I use more than 1 focus point.

And how do you do that in such a short time? Does your camera have option of selecting, say, 3 AF points, or it selects automatically as many as required?

 

[rexbobcat]

For tracking motion.

Also; with incredibly "bright" lenses such as an 85mm f/1.2, recomposing can actually throw your intended focus point out of focus because the depth of field is so shallow.

 

[Benco]

It helps when you have a really fast moving object to focus on like a flying bee etc. That is the only time I use more than 1 focus point.

And how do you do that in such a short time? Does your camera have option of selecting, say, 3 AF points, or it selects automatically as many as required?

Yes, with my camera you can set it to start with one point but then it will try to track the object using a previously set number of points surrounding (9, 21 or 39) depending on how you wnat the camera to respond.