The better approach might be to rename the sensors
FF sensor: 0% mm "boost", 0+ f-stop boost (REFERENCE)
APSC sensor: ˜70% mm boost,
M43 sensors: 100% mm boost, +2 f-stop boost (two ticks higher)
The problem is not what's on the lens at all. It's the people that insist on using other sensor sizes or to be defined in terms of the kings of kinds, the size of sizes, the magnificent, ever-loved, insuperable rectangle of 36mm x 24mm (or diagonal).
I mean, I still don't understand why the plank constant isn't expressed in relation to the photographic constant of action.
What is the advantage of bringing the sensor size into the mix? In terms of the resulting image it isn't important.
So I can talk about lenses that are the same, as the same, and lenses that are different, differently. So that if I use one lens in a body with a different sensor size, I am not saved anything with FoV as it changes, and the same mm don't tell me about the DOF.
Why is it important to talk about a 50mm lens on a 2X crop body as being the same as a 50mm lens on a full frame? Those two lenses will give very different results.
Maybe because we are actually talking about the same exact lens? I get your point, and don't dislike FOV. However, this could be a choice in the camera display...user selectable. I don't think the FOV depends on the lens but on the lens + actual camera. This makes sense to anyone getting started, especially since mm will confuse them even more. However, I am not sure lenses need to stop saying MM. It's actual fact that is very useful, and describes properties of the lens. Can this book be translated into two other languages?
If you are using the same lens on multiple bodies, then there's no advantage to calling the lens 50mm/80mm, instead of a 46.8°/29.9°
The lens is certain mm in FL regardless of the system. It'd be the same to talk about equivalent FOV and equivalent FL for me with a little practice. Not sure others.
When the lens is used with multiple systems, you need to track specs for each system either way.
Yes.
The reason we traditionally need to know about the sensor is to get the light per unit area into the sweet spot of the film's response curve.
With a car transmission we only need the ratio of input RPM to output RPM. We don't need to know the gear ratios of the intermediate gears.
With digital, we can treat the camera as a "black box". That makes the camera much easier to teach.
I do still tell the black box what aperture I want, be it in mm, f-stops or any other metric that may be wanted from me.
Yes. But if you tell the black box you want a 12mm aperture, you can use that same spec for any camera. If you say f/4, then you may need to do a conversion to get the same results from a different camera.
Not really. That you use that example illustrates the point. How do you set 12mm aperture on a phone? You can't. But you also have a point. What does f2.8 means in an iPhone if I don't know how it affects how much is OOF in a scene. The mm at least tell you a lot more (without needing to convert).
So I think f-mm would work though too. Not sure of the implications to others. However, you are missing a critical point: NOT ALL APERTURES ARE ROUND. I have a triangular Rollei lens. How to I measure it? Do I now start using equivalent mm for each type of lens? What about square apertures? I think the stops are calibrated so they actually measure light doubling and halving at the marked stops. In mm, what would that mean? Equivalent f-mms? If in auto-mode, the camera can do whatever it wants...it still relies on being able to double or half. Does the camera need to know the f-stops then, without me knowing? And then what, it displays them in equivalent f-mms to me and on Exif?
The photographer needs to know the angle of view, and aperture diameter. Those affect the final image uniformly the same, no matter what the sensor size.
Which DOF jump is much bigger, 1mm to 3mm or 3mm to 6mm, or 6mm to 9mm? Do I need to memorize the circle surface formula along with the value of PI? I can call the stops 0, 1, 2, 3, 4, 5 too. But I want them to be spaced ideally in increasing proportions of surface of area. Or would you use a linear scale? And how more mm would allow me to double the shutter speed? You'd replace f-stops with mm-stops.
Aperture diameter varies the same as f/stop. The difference is that the f/stop is adjusted by the focal length.
If it where a perfect circle.
In therms of DoF and the other factors, there's no difference.
The characteristics of blur and soft/hard focus are affected by aperture shape. Again, I am not arguing against the idea of mm. I am just pointing how there are trade offs where you didn't think there were any.
The difference is when comparing to other cameras, which may have different sensor sizes.
If you want to match a shot that was taken with a 12.5mm aperture diameter, you need 12.5mm no mater what the sensor size.
So what is the correct scale for all cameras and sensor sizes? Do we start with f1 on FF? And measure equivalent f-mm for that? We are saving a division...for all the trouble? And the mm may not even be mm, due to aperture shapes. I still like f-mms. I think until I started using manual aperture lenses, I did not even understood the f-stop implications "physically". My canon metered wide open, and the body changed the aperture. Nothing ever happened. With manual lenses, I had no problem with f-stops. But mm would bemore visual. However, it's just a division of FL and aperture. However, that division is not stated by the lens. The aperture is usually not a circle, only wide open it is.
If you are want to match a shot taken at f/4, you need to use a different f/stop if your camera has a different sensor size.
Yes.
As things are now, we know that f/2.8 is a fast lens on a full frame, but not so "fast" on a small sensor. We know that f/11 is a not small enough to worry about diffraction on a full frame, but is small enough for a small sensor camera.
So long as all lenses are fixed or never used with a different sensor size. This also confuses a bit a lens optics. Now Zeiss may have a 60 degree wide angle Distagon, and another 60 degree Planar, why do lens makers need to always be changing designs? Lenses will be named the same, with absolutely different kinds of constructions of all sorts. Someone "discovers" the Zeiss 60 FOV FF is exactly similar to the 120 VOF M43. Which sensor size 60 FOV are you using on this shot?
I am not saying what you say doesn't make sense. I am saying, the camera can display mm and FOV or FL and f-stops, or any combination you like.
The issue is the same no matter how you label.
Exactly. The 50mm lens doesn't become 100mm, it is only equivalent. A $1 bill isn't $20 pesos. The FOV is a property that does not belong to the lens, and therefore, it's a 28 degrees lens does not even exist. The diameter of the triangle does not exist. And so on.
We know that the DoF of f/8 varies with sensor size.
On the other had a 40° angle of view and a 12mm aperture gives us the same DoF, same diffraction, and at the same shutter speed the same noise on all sensor sizes.
Yes. That's cool assuming you keep each lens to one sensor size always. And that you don't want to know anything about which optics you like, as that again requires talking about Equivalent DOFs and Equivalent aperture mm. And the Aperture mms also would not be spaced linearly, you'd have a progression more like f-milliliters scale.
Every lens would need to indicate FOV and also sensor size. And same exact lens for more than one mount, would need to state it's a different FoV when it's not.
Are there many lenses that get used with more than two sensor sizes?
It depends. Most, will never mix them. It's whatever came with the camera, or most often just 1 or 2 more lenses of the same system.
If not, then you just need to label a lens with at most 2 values.
Agreed. FOV and (real) mm or mm and equivalent mm (maybe).
Ultimately, you can't get away with knowing the sensor size. But I don't dislike FoV/mm, I think it's just a trade off. It will also be incorrect to say it's an 80 FOV lens without also adding the sensor size. Would this make me mad? No. Does it has drawbacks, yes.
M43 lenses typically only get used on M43 bodies. You only need to label one angle of view.
Tell that to millions of adapted lenses, from TV, film, rangefinders, projectors. For the average person, I agree.
Canon crop lenses only get used on Canon crop bodies. You only need to label one angle of view.
Canon full frame lenses can be used on either crop bodies or full frame. These would get 2 labels.
Yes, there are odd uses and exceptions, but these are he exception rather than the rule. If we are teaching a beginner how it works, we probably don't need to start with an explanation of what happens to Angle of View if you mount a full frame lens to an iPhone.
What prevents you from teaching in terms of FoV? I think you want something different. That for the vast majority, a FOV equivalence and equivalent f-mm would be easier to move them between sensor sizes. And I agree. From that perspective. I'd also be nice the Imperial units dissapeared tomorrow (for me), that everyone spoke only english, and that everone used USD. But life, and for physical reasons too, it's a little more complicated.
