Beginner Back button and auto focus

[JennyGW]

Honestly, if you are hitting focus on the wrong spot (background) that is probably not the servo mode. If you are getting soft or out of focus that could be do to the servo mode.

No, I know how my camera works, thanks

 

[Scooter]

That's a complete myth. live View focuses by contrast. It doesn't employ all the focus points. If you're using live view then you are not using the cameras AF to its full potential.

That's not quite right: when you focus (using the slow contrast detect AF or manually) in live view it is using the actual image sensor. It will be right, every time.

When you use the separate AF sensor, or judge focus manually in the optical viewfinder the light has taken a different path entirely to the one it will take to the image sensor to make the picture. The two can get out of whack.

Live view AF may be slow, but it will be right. The points on the AF are not used at all in live view: the light doesn't reach them.

It's not the answer for AF though. If AF sensors didn't work our cameras would not have them, and the answer is to calibrate with each lens, but if you find that all of em are out by some way, there's probably something not quite right with your mirror, AF sensor or prism;get the camera tested and serviced.

 

[Phil V]

That's a complete myth. live View focuses by contrast. It doesn't employ all the focus points. If you're using live view then you are not using the cameras AF to its full potential.

Well do you agree with it or not?

That's not quite right: when you focus (using the slow contrast detect AF or manually) in live view it is using the actual image sensor. It will be right, every time.
...

Seems to disagree...
Except it's actually a completely different point, because what Nick said was this...

The points on the AF are not used at all in live view: the light doesn't reach them.
... If AF sensors didn't work our cameras would not have them, and the answer is to calibrate with each lens, ...

So you agree then.

 

[James Wheeler]

I use both configurations.

BBF I have found useful for wildlife where you're sat on AI Servo (makes sense to be here as faffing with switching it will lose you some shots if you suddenly need it) so you can focus and recompose. I shoot with my right eye so I can keep the other open which helps me locate unpredictable targets more quickly for some reason.

Shutter release button focusing I prefer for airshows because having my thumb on the AF button on the back of the body doesn't give me as stable a point of contact with the camera as I would like for panning shots. I also shoot with my left eye at airshows so my eye socket, chin and right hand all provide stabilising points of contact. Sounds weird but works OK for me...

So, pick and choose depending on what best works for what you're doing! It is a quick setting to change on my camera anyway.

 

[Scooter]

Hi Phil,

I disagree with BC that getting better focus on live view is a myth. You can (even though it's not really something you'll do most of the time).

He also said you don't use *all* the AF pints focusing in live view implying you do use some of them, which is not the case.


Owen

 

[Blank_Canvas]

Hi Phil,

I disagree with BC that getting better focus on live view is a myth. You can (even though it's not really something you'll do most of the time).

He also said you don't use *all* the AF pints focusing in live view implying you do use some of them, which is not the case.


Owen

Well you have to use at least one at least one focus point in LV , you may well disagree with me but like it or not, if you are using Live View AF your not using your cameras AF system to its full potential. Ipso facto. That's not a myth it's implicit. In fact your camera manual will probably point this out, certainly the Nikon ones do.

Note I said, focus point, not AF point. There is a difference. live view focus by 'contrast' as opposed to to AF phase-detection via the mirror.

 

[Scooter]

It's not something you can debate or have different opinions on. The AF sensor is not used at all in live view. No light reaches it.

I agree you would use the cameras AF system most of the to time.