Something I've noticed about the 3GS autofocus / touchfocus

[danpass]

As we know the 3GS camera picks a spot and focuses on it. We also know that touching a spot on the screen overrides the camera choice and in addition adjusts the exposure accordingly.


I was taking some outdoor shots today and it seems that, even if the two focus spots are the same, that camera autofocus and touchfocus on the same spot will yield different exposure results.

Touchfocus will essentially establish a spot meter in conjunction with the smaller focus area.


I'm going to continue testing further to confirm.

 

[Merkie]

No need to confirm this, this is a known feature of the 3GS camera.

 

[BittenApple]

Tap to focus.
Autofocus keeps things sharp, and a macro lens takes great close-ups. But you can also tap the iPhone display to selectively focus on anything in the picture — a face in the background, for example.

From Apple's website.

 

[blulegend]

I've had poor success with getting the iPhone 3GS to spot meter. It seems to always revert back to its own full-scene metering. I find that most of the time, my subject is grossly underexposed by the iPhone and I can't get it to spot meter.

 

[kas23]

From Apple's website.

He's not talking about the fact that it focuses on one spot, but about it spot metering only the small area you tap, not the whole frame. That is, if you tap-focus on a very bright small area and snap a pic, the whole shot is going to be grossly overexposed.

 

[panoz7]

He's not talking about the fact that it focuses on one spot, but about it spot metering only the small area you tap, not the whole frame. That is, if you tap-focus on a very bright small area and snap a pic, the whole shot is going to be grossly overexposed.

I think you mean underexposed.

 

[CalMin]

I think you mean underexposed.

Depends on the conditions and subject.

 

[panoz7]

Depends on the conditions and subject.

I was commenting on this quote by kas23:

That is, if you tap-focus on a very bright small area and snap a pic, the whole shot is going to be grossly overexposed.

If there's a small part of a photograph that's very bright and you tap on it, the iphone, at least according to this thread, reverts to spot metering and attempts to properly expose that very bright section at the expense of the rest of the image. Kas23's hypothetical area is much brighter then the rest of the image so in order to make it a reasonable brightness the camera's going to have to underexpose the rest of the picture. Kas23 had the right idea... I think he/she just said it backwards.

I can't think of a single situation where spot metering on a small bright section of the photo would result in a grossly overexposed picture.