Iphone aperture equivalence? Does the f1.78 wide lens let the same amount of light in as the equivalent "full frame" lens?

[wallpaperviking]

Hi,

Apologies if this has been discussed, I did search and could not find an answer. If using the new Iphone Pro, does the main (wide) lens have the "light gathering ability" of F1.78, whilst having the "equivalent" D.O.F of f6.2.. ie if shooting a full frame camera at f1.8 and the Iphone, would they look the same in terms of the brightness of the scene? Thanks!

 

[MGrayson]

It's true that a point on the sensor (not a pixel, a point) sees a circle of light whose angular size is determined only by the (true) f-number.

The "equivalence" issue is a favorite flame war igniter, so I'll state a well defined version. Your goal is to take the same picture with two cameras, A and B. B has a sensor x times as large as A does. Then to get the photo of the least difference (that is, if you change any of these numbers, there will be a common situation where the photos will look very different), A and B must be in the same location, you multiply B's focal length by x, you multiply B's f-number by x, you multiply B's ISO speed by x^2 (I think - a test just now was consistent), and you keep the shutter speeds the same. These are required by (in order) Geometry, FoV, DoF, Brightness (Ev), and motion blur. The reason this issue causes wars is that some people only care about a few of these. If your subject is stationary, then the shutter speeds needn't agree. If you are focusing at infinity, DoF doesn't matter, etc.

Matt

 

[wallpaperviking]

It's true that a point on the sensor (not a pixel, a point) sees a circle of light whose angular size is determined only by the (true) f-number.

The "equivalence" issue is a favorite flame war igniter, so I'll state a well defined version. Your goal is to take the same picture with two cameras, A and B. B has a sensor x times as large as A does. Then to get the photo of the least difference (that is, if you change any of these numbers, there will be a common situation where the photos will look very different), A and B must be in the same location, you multiply B's focal length by x, you multiply B's f-number by x, you multiply B's ISO speed by x^2 (I think - a test just now was consistent), and you keep the shutter speeds the same. These are required by (in order) Geometry, FoV, DoF, Brightness (Ev), and motion blur. The reason this issue causes wars is that some people only care about a few of these. If your subject is stationary, then the shutter speeds needn't agree. If you are focusing at infinity, DoF doesn't matter, etc.

Matt

Hi Matt,

Thanks so much for the reply...

Maths was always far from my strongpoint so most of your post was lost on me I am afraid...

I guess what I am really interested in, is whether the Iphone lens acts more like a f1.78 or more like a f6.2 in dark situations? I am only interested in light gathering ability, not D.O.F...

My basic (non mathematical) assumption derived from apple/internet is that it has the full frame equivalence of f1.78 (light gathering ability only) and the D.O.F equivalence of f6.2.

Is this roughly correct?

Thanks!

 

[MGrayson]

Hi Matt,

Thanks so much for the reply...

Maths was always far from my strongpoint so most of your post was lost on me I am afraid...

I guess what I am really interested in, is whether the Iphone lens acts more like a f1.78 or more like a f6.2 in dark situations? I am only interested in light gathering ability, not D.O.F...

My basic (non mathematical) assumption derived from apple/internet is that it has the full frame equivalence of f1.78 (light gathering ability only) and the D.O.F equivalence of f6.2.

Is this roughly correct?

Thanks!

Short answer: Yes.
Longer answer: Yes, but so what?

All that matters is how well the camera (and processor) does in any given situation. The color accuracy of a phone camera in low light is unreasonably good.

Phone pic:



Medium format pic - same f-stop



The former was much easier to take. The latter is a different animal (pun intended).

Matt

 

[wallpaperviking]

Short answer: Yes.
Longer answer: Yes, but so what?

All that matters is how well the camera (and processor) does in any given situation. The color accuracy of a phone camera in low light is unreasonably good.

Phone pic:



Medium format pic - same f-stop



The former was much easier to take. The latter is a different animal (pun intended).

Matt

Cheers Matt, much appreciated!