About the infinity focus of lumia phones.

[cdanieljohn]

Camera (Distance ?) Subject
Smart phones like lumia, lumia 525 in my case, have fix f2.4 so the depth of field is not much a big factor to control?
So i'm using nokia camera's infinity focus in taking distant photos.
My question is how long should be the distance to the subject to get more effective shot? Like 5 feet away or more?

 

[AndyM72]

Do you really mean the hyper focal distance?

 

[cdanieljohn]

Do you really mean the hyper focal distance?

I'm not even sure what i'm saying lol, but the distance of the subject to the camera when using infinity focus?

 

[AndyM72]

Infinity focus means "parallel light is focused". Light emitted or reflected by a point source can only arrive at a lens as parallel light, if that point source is an infinite distance away.

In practice, the light is as near as makes no difference to parallel once you focus on something about a kilometre away. The horizon is usually somewhere between 4 and 5 kilometres away.

Since you know about the concept of depth of field, the theory is that at infinity focus, the depth of field (depth that appear to be in focus at typical print sizes) starts at the hyper focal distance and ends at... infinity ;-)

 

[AndyM72]

My advice to you is focus on the thing furthest away that you still want to appear sharp. The 525 camera has such massive DOF that everything more than a metre away will look okay.

 

[cdanieljohn]

Infinity focus means "parallel light is focused". Light emitted or reflected by a point source can only arrive at a lens as parallel light, if that point source is an infinite distance away.

In practice, the light is as near as makes no difference to parallel once you focus on something about a kilometre away. The horizon is usually somewhere between 4 and 5 kilometres away.

Since you know about the concept of depth of field, the theory is that at infinity focus, the depth of field (depth that appear to be in focus at typical print sizes) starts at the hyper focal distance and ends at... infinity ;-)

Thanks i learned something.
For my device which only has 5mp, does this apply? It seems that we can use infinity focus even if the subject is not kilometers away?

My advice to you is focus on the thing furthest away that you still want to appear sharp. The 525 camera has such massive DOF that everything more than a metre away will look okay.

Okay thanks ill try it myself

 

[AndyM72]

Thanks i learned something.
For my device which only has 5mp, does this apply? It seems that we can use infinity focus even if the subject is not kilometers away?

It is unrelated to the sensor, just the lens.

I've just been trying out the Nokia Camera app on my Lumia 630, and it seems to "cheat". The manual setting just before "infinity" is obviously more out of focus for a subject a couple of metres away than the infinity setting. So the infinity setting seems to actually be choosing the Hyperfocal distance instead, it is not choosing infinity focus at all. After I found out the true specs of the Lumia 525 camera, I worked out the hyperfocal distance to be about 110cm. The theory says this is the focal distance when you get maximum Depth of Field, because it is the closest distance the lens can be focused to while keeping objects at infinity acceptably sharp. So the depth of field area (the distances that will look like they are in focus) will start at half the hyperfocal distance and end at "infinity" (so everything as far as the lens can see).

However, Depth of Field is itself a cheat. Notice I said that Depth of Field is only the distances that look like they are in focus. There is only one distance that is really, truly in focus. All the other distances in the depth of field region are slightly out of focus, but on a screen or a photo print viewed at normal distances, the amount of out of focus is so slight that your eyes cannot see it. This is why the definition (which I stole from Wikipedia) says "acceptably sharp". Now, if you took that image, blew it up to the size of a billboard and stood a metre away, you'd then see that much less of the image than you originally thought is actually in focus. But the point is, no one looks at billboards from a metre away, except the guys that stick them up there! At that distance, they look awful, blurry and pixelated.

It is for this reason that a much better rule to stick to, is to focus of the furthest object away that you want to be sharp (so use Autofocus, half press the shutter, then tap on the thing in the distance on the screen). The thing you focus on will be super sharp, and everything closer up to 110cm away will be "acceptably sharp".

 

[cdanieljohn]

It is unrelated to the sensor, just the lens.

I've just been trying out the Nokia Camera app on my Lumia 630, and it seems to "cheat". The manual setting just before "infinity" is obviously more out of focus for a subject a couple of metres away than the infinity setting. So the infinity setting seems to actually be choosing the Hyperfocal distance instead, it is not choosing infinity focus at all. After I found out the true specs of the Lumia 525 camera, I worked out the hyperfocal distance to be about 110cm. The theory says this is the focal distance when you get maximum Depth of Field, because it is the closest distance the lens can be focused to while keeping objects at infinity acceptably sharp. So the depth of field area (the distances that will look like they are in focus) will start at half the hyperfocal distance and end at "infinity" (so everything as far as the lens can see).

However, Depth of Field is itself a cheat. Notice I said that Depth of Field is only the distances that look like they are in focus. There is only one distance that is really, truly in focus. All the other distances in the depth of field region are slightly out of focus, but on a screen or a photo print viewed at normal distances, the amount of out of focus is so slight that your eyes cannot see it. This is why the definition (which I stole from Wikipedia) says "acceptably sharp". Now, if you took that image, blew it up to the size of a billboard and stood a metre away, you'd then see that much less of the image than you originally thought is actually in focus. But the point is, no one looks at billboards from a metre away, except the guys that stick them up there! At that distance, they look awful, blurry and pixelated.

It is for this reason that a much better rule to stick to, is to focus of the furthest object away that you want to be sharp (so use Autofocus, half press the shutter, then tap on the thing in the distance on the screen). The thing you focus on will be super sharp, and everything closer up to 110cm away will be "acceptably sharp".

So 4 feet distance it's still better to use autofocus?