That said, at least with stand-alone camera manufacturers you can usually work out what the real specs should be if you’re in the know.
For exposure purposes, f1.5 is the accurate and most important spec for that lens. All mirrorless camera lenses are specced accurately with focal length and fstop. Perhaps some of the marketing is done with 35mm “equivalent” specs but I’ve never seen a lens that had anything but the actual measurements on them. I’m not sure why people are still referring to 35mm focal lengths when talking about FOV in any case. Nobody is comparing the lens on an iPhone with one on a camera with a 35mm sized sensor. Certainly nobody will use the iPhone lens on another camera.
The main sensor on an iPhone is larger than most phone cameras but still close enough that touting the f1.5 fstop does indeed mean that it lets in more light, has a larger aperture, and has a narrower DOF than many other phone cameras. The vast majority of iPhone users have never shot with 35mm cameras and so wouldn’t have any idea what you’re talking about when it comes to 35mm DOF. I wish companies would ditch the 35mm normalized specs altogether.
This is a very common misunderstanding. To whatever extent the camera "looks like" it's using a 35mm-format f/1.5 lens from an exposure standpoint, it's only because the sensor gain is turned way up to compensate. As a result, SNR is worse, so it's like you took a darker exposure on a better camera and then cranked it up in post.
All of this nonsense started with digital photography. There was close to a century of shooting with different formats and lenses without ever trying to twist what an f-stop meant. Open up an ASC handbook and you'll find DOF charts for different formats and lenses but no talk of equivalent anything.
I want to know the actual specs of a lens, that is how you can compare with similar systems. I wish Apple would drop the now irrelevant references to 35mm. I also wish people would stop confusing a physical measurement with a quality target. To reiterate, I find the concept of equivalent f-stops to be nonsensical and think they only confuse the issue.
Which tells you precisely nothing at all without having other specs to multiply it out. It's a useless spec, in the format presented by Apple.
> gauge some arbitrary level of performance
The fact that it's arbitrary is irrelevant; the important part is that it is a consistent reference point across cameras.
> I wish Apple would drop the now irrelevant references to 35mm.
Yes, that would be ideal, but they're not going to do that, so at the very least they should just be consistent with the specs they provide.
Like I said before, trying to normalize different aspects of images and the resultant quality by trying to make f-stops something they aren't only confuses and obscures what is actually happening and prevents sensible discussions of camera systems.
The 35mm equivalent focal length is used just to give an idea about FOV. I wish they would just give us the angle of view in degrees instead. Then maybe people would stop trying to mangle what fstops means in regards to DOF, the amount of light the sensor sees, SNR etc. Compare similar sensor systems, stop trying to cram one into the other.
This number in isolation is completely useless for telling anything about how the resultant image is going to look. As opposed to, say, equivalent focal length, which tells you valuable information (about FoV) independently of any other spec.
> I wish they would just give us the angle of view in degrees instead
I agree, it would be nice if they just used invariant specs for everything. FoV angle and linear aperture diameter would be sufficient for most use cases.
And I've got a non-35mm mirrorless camera. All the lens I've got are marked with the true focal length and true f/number, not some "equivalent". My iPhone camera photos' metadata show the focal length, both true and "35mm equivalent".
You're not disagreeing with my actual argument, which is just "they should use the equivalent ratings for both focal length and f-stop". If you prefer physically-based specs, you should be demanding that they also say the focal length is 7mm or whatever.
> It's important for shutter speeds, and relative performance in low light
It's completely useless for determining low-light perf without knowing the crop factor.
> I can compare roughly a phone camera that's at f/1.5 vs a phone camera that's at f/2
Not without knowing the crop factor. You're falling for the marketing.
The depth of field on the other hand does depend on the size of the lens (or hence the size of the sensor the lens focuses it's incoming light on).
Let's take an 18mm F/2 lens on a Micro-Fourthirds camera. Those have a 2x ratio of sensor size compared to a full-frame sensor. So this 18mm lens would be an (2x18=36mm "equivalent") full-frame lens, meaning the perspective of said 18mm would be the same perspective a standard 35-36mm full frame lense would have. This 18mm F/2 lens would be F/2.0 based on the amount of light it lets in. That's the ratio of said lenses focal length to it's entrance pupil. Only in terms of "how the background will blur" we multiply this by 2 to show what the visual effect of this would be.
So really the best way of saying it would be "hey this is an 18mm/F2 Micro Four Thirds lens (36mm, F2/F4 equivalent).
Personal opinion: Even better if we used a different acronym for depth of field, say d or doF or something. Then we could say "36mm f2.0 DoF4.0"-equivalent lens.
So in the iPhone 14PM main camera case we'd call it a "28mm f1.78 DoF8.1"-equivalent as it has an about 4.6x sensor size crop factor from full frame.
(and f1.78 for actual f-stop light performance)
When you get close enough you can actually take proper bokeh producing shots. It's actually becoming hard to be fixed aperture as some closer shots would require a higher f-stop number already to be properly in focus.
I find this way of describing the iPhone cameras frustratingly misleading. It's not the author's fault; Apple does it in their official specs.
The "26mm" rating is "equivalent", meaning "this looks like a 26mm lens on a 35mm film camera". It basically tells you the FOV angle.
The "f/1.5" rating is not equivalent. It's very dishonest to mix and match equivalent and non-equivalent specs, because it makes the lens sound a lot better than it is to non-expert readers. If they were being honest, the equivalent aperture would be a lot smaller, like f/16 or something.
Every other camera mfg I am aware of will consistently use equivalent or non-equivalent for all specs, and make it clear which they are using.
For example, most mirrorless camera lenses are spec'd non-equivalently, meaning that a "26mm f/1.5" means "if you put this lens on a 35mm camera and extrapolated the output to cover the whole sensor, that's what you would get". To understand what it will look like on a different sensor, you multiply 26 and 1.5 by the crop factor.
In Apple's case, it's actually impossible to tell what the image will look like from the specs without looking up the crop factor, which of course they don't advertise front and center like they do this misleading tuple of specs.
In general, lenses with smaller f/N aperture values tend to be better and more expensive (because they have a larger aperture, let in more light, narrower depth of field), so if you don't mind misleading customers, you just pick the smallest denominator you can get away with.