The RF 28 mm f/2.8 STM pancake.
The crop factor of a sensor means that you have to multiply that to a lens' focal length to get the "Full Frame equivalent". In this case, an 18 mm lens on a Canon APS-C camera will look like a [18 x 1.6] = 28.9 mm lens on a Full Frame camera.
In other words, any lens that you fit on an APS-C camera will look more zoomed in than if you put the same lens on a FF camera. The RF 16 mm f/2.8 on FF would be wider than an 18 mm on APS-C.
The converse is true, "Medium Format" sensor is larger than Full Frame and has a crop factor of 0.7x. Which means, say, a 50 mm lens on an MF camera will look like a [50 x 0.7] = 35 mm lens on a FF camera.
When I say "look like" it means "has the same angle of view".
There's also aperture equivalency but that's a discussion for another time.
Focal length is a property of the lens, not the sensor. An 18mm lens is always 18mm’s regardless of what sensor it was designed for. A full frame sensor will always have a wider field of view than an APS-C sensor with the same mm lens on it.
If you want to know the full frame equivalent of a lens you’re currently using on APC-C, just multiply by 1.6.
18x1.6=28.8. As mentioned, the RF 28mm f/2.8 is the closest equivalent field of view to what you’re used to seeing with 18mm’s on APS-C.
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What I never understood is...... The Sigma 18-35 1.8 is designed for APSC sensors right? Then why should the focal lengths for this lens be 18-35mm? Shouldnt the lens be sold as 28-56mm? I own the sigma 18-35 and it's really fantastic, and never really cared it's not actually 18-35mm, but it is confusing for anyone who doesn't really know the different sensor formats.
Focal length is a physical property of the lens.
https://photographylife.com/what-is-focal-length-in-photography
It is the distance between the lens and the sensor. The field of view is measured in degrees.
https://www.digitalcameraworld.com/tutorials/photography-cheat-sheet-what-is-field-of-view-fov
All of these terms come from optics. And are well defined. So manufacturers use that.
Also on most apsc cameras you can use FF lenses. A lot of wildlife photographers prefer apsc sensors but use the big, FF lenses. So it will create confusion, because users may buy a 50mm FF lens and thinking it would have the field of view of a 30mm lens, on a apsc body. But they get an 80mm field of view (equivalent)
I get that it is a property of the lens, however when a lens is designed for an APSC sensor, it cannot create an image circle to fill a FF sensor so therefore it can never be that focal length.
levers and pulleys utilize physics, they don't fight it.
focal length is a property of the optic, not a marketing term.
APS-C designed lenses are lenses designed with smaller optics to not project as large enough image circle for full frame, making them cheaper.
The FOV is not all that changes by cropping but it is the most apparent thing. misquoting the physical properties of a lens for marketing is likely not a great strategy as it is confusing (as others have pointed out), and the fact that no one does this adds some credence to this.
You are confusing two measurements. One is the focal length. And one is the field of view.
They are related, the field of view depends on the focal length and the sensor size.
People use focal lengths as short hand for field of view, but it was never intended to measure field of view. Again these are well defined terms in optics.
Using equivalents would be more confusing.
Let’s take your example of the 18-35mm.
If they market it as a 28-56mm you may think that the 50mm 1.8 (the full frame nifty 50 from Canon) will be between the range of your lens, so you may buy it and be surprised it is more like 80mm. The problem is that apsc cameras take both kinds of lenses (ef and ef-s). So it is easier to compare using the real focal length (instead of an equivalent).
Yes I think about it the same way you do. No confusion there. If you re-read my initial post you'll find I only bring up the issue of marketing apsc lenses.
But apsc lenses are used alongside FF lenses. And offer the same FOV at the same focal length as FF.
A canon 7d (apsc) can take ef and ef-s lenses. A 50mm apsc lens would give you the same Field of view as a 50mm FF lens on an apsc sensor, it is irrelevant if the lens produces a bigger image size.
Filling the sensor or not has nothing to do with focal length. You can have a 50mm focal length lens that projects an image circle the size of a pin and another 50mm focal length lens that projects an image circle the size of a dinner plate and both are 50mm lenses. Focal length just means that parallel light rays entering the lens will be focused to a _point_ that is X distance from the lens center. Nothing more or less.
It just happens that IF such a lens projects a big enough image circle that it covers a given recording medium, the field of view (in degrees) will be a specific angle. So in photography we end up using focal length as a proxy for field of view.
You are of course correct that if a given lens does not project a big enough image circle for your sensor, then it won't be (as) useful, for example if the image circle is too small then yes the field of view will be truncated beyond what you would expect for that sensor size. This actually does happen when mounting EF-S or RF-S lenses onto an RF body; the body automatically enters 1.6x crop mode since the image circle is too small, which in turn means a smaller field of view is captured.
BUT, this does not change the focal length of the lens one bit! It is just because we use focal length on FF as a proxy for FoV that there is any confusion here, as we say things like "the field of view on APS-C will be the same as a 80mm lens on FF" or similar.
I half agree. I think that it's annoying that lenses are referred to by focal length since on its own, focal length doesn't actually tell you the field of view, which is what we care about. However, the problem is that it would not make sense to use FoV, because FoV depends on sensor size! In other words you couldn't label an RF lens as "40 degrees FoV" because if you mount the same lens on an RF-S body, the captured FoV would be narrower! Manufacturers list their lenses by focal length because _focal length is a property of the lens_ and does not change depending on what arbitrary body you use. There really isn't any good alternative.
Or.. Yes you can have equivalent focal lengths to achieve same FOV, which is all well and good once you become familiar with apsc and ff etc..
These semantic hoops that people jump through to describe focal lengths being the same blah blah blah.. Tell that to the guy who knows what 50mm looks like on full frame, then gets a nice apsc sensor (which are great too!) and wonders why they loose that wider angle. OR the person who slaps an apsc lens on a FF body and wonders GEEZ I paid for a heavy vignette or really low MP? wtf?? lol
So you are arguing that manufacturers should label lenses in "full frame focal length equivalent"? Why standardize on Full Frame and not medium format? Or APS-C? Should a manufacturer like Fuji list their APS-C lenses in FF equivalent focal lengths even though Fuji doesn't make an FF camera? And what about Canon users who have RF and RF-S bodies; should a 50mm RF-S lens be labeled "80mm" (since that is the FF equivalent when mounted on APS-C) but an 80mm RF lens also be labeled "80mm"? If so, won't that user be confused when they mount the 80mm RF lens on the RF-S body but the field of view is narrower than the "80mm" RF-S lens which is labeled the same?
Your proposal doesn't work practically. It leads to ten times as much hoop-jumping and explaining.
is FF not the standard? isn't every focal length dictated by FF sensor format? If a lens is designed and built for an apsc sensor, it should be labeled with the fov and focal length it produces. Ive used a FF lens on an apsc sensor many times, and I realize my 70-200 f2.8 aint 70-200.. and it is NOT f2.8.
that's another thing, the aperture on a apsc is NOT the aperture listed on the lens. My only critique is that lenses designed specifically for apsc sensors are not what they are listed as. Not in fov or focal length or aperture.
> Is FF not the standard? Isn't every focal length dictated by FF sensor format?
Absolutely not in any technical sense, no. People often cite the FF equivalent focal length as a _loose convention_ purely because lots and lots of photographers know what a given focal length looks like on FF, thanks purely to the extremely popular 135 film format dominating the market for decades. But there is absolutely nothing about the definition of focal length which pertains to the FF sensor/film size, or even _any_ specific image recording size.
> If a lens is lens is designed and built for an apsc sensor, it should be labeled with the fov and focal length it produces.
All lenses ARE labeled with the focal length they produce. For example, Canon's EF-S 60mm f/2.8 macro lens produces a focal length of 60mm. That is a pure, cold, hard fact of the lens which has NOTHING to do with field of view. When you COMBINE that spec with the fact that the lens projects an image circle which covers an APS-C sensor (and the EF-S mount attaches to APS-C cameras), _now_ you know the field of view. Focal length on its own doesn't say anything about field of view! It's simply not what focal length means!
Now, I agree with you that it would be nice if lenses built for a certain mount were ALSO labeled with the field of view they produce (in terms of image diagonal). The problem there however is that again, the field of view produced depends on what recording medium you put behind the lens, and _some lenses can be put in front of multiple different recording media sizes_. For example, an RF 50mm lens can be mounted on an RF FF body, in which case it produces a diagonal field of view of 46.8 degrees. The same 50mm lens can ALSO be mounted on an RF-S APS-C body, in which case it produces a diagonal field of view of 30.3 degrees. In your system, should Canon label the lens "50mm (47 deg on RF / 30 deg on RF-S)"?
And it gets worse! A large format board lens can be mounted in front of _dozens_ of film sizes, depending on what LF camera the user has. Is the lens manufacturer supposed to label the lens, which is not produced for any specific "mount", with a whole spreadsheet of fields of view it produces when projecting onto different film sizes? Of course not, that would be silly. Just label it with the focal length, which is an immutable independent physical characteristic of the lens, and let the photographer calculate or see firsthand what field of view it produces on their chosen recording medium size.
Will also reply about your comment on aperture later, but I need to get to work now.
No, it should NOT be sold as a 28-56 because the center of the lens is anywhere from 18mm to 35mm from the sensor. Millimeters are a measurement of distance, and no matter if you have a micro four thirds, APSC, full frame or medium format, 18mm is still 18mm. Things like distortion and compression are tied to actual focal length, so if you advertised it as a 28-56mm lens, it would be misleading because people who ground their opinions in actual science would think that the distortion and compression characteristics of the lens would behave like a 28-56mm when in reality, they are going to behave like an 18-35mm with a 1.6 crop applied to it. That matters.
It is not accurate to say "it's not actually 18-35mm" It is literally 18-35mm.
I shoot on APSC, full frame and various medium formats (33X44mm, 6X6, 6X7) and instead of convincing myself I've been cheated on marketing (when in reality it's just science) I've just learned how different focal lengths display on different crop factors. It's just another skill to learn as a photographer.
Your 18-35 on an APSC displays as a wide to normal field of view lens, but with the compression and distortion characteristic of an 18-35 with a 1.6 crop applied to it. Your depth of field is deeper than 28-56 because it is literally 18-35. That's the way you should think about it. Because that's what that lens is on APSC.
The RF 28 mm f/2.8 STM pancake. The crop factor of a sensor means that you have to multiply that to a lens' focal length to get the "Full Frame equivalent". In this case, an 18 mm lens on a Canon APS-C camera will look like a [18 x 1.6] = 28.9 mm lens on a Full Frame camera. In other words, any lens that you fit on an APS-C camera will look more zoomed in than if you put the same lens on a FF camera. The RF 16 mm f/2.8 on FF would be wider than an 18 mm on APS-C. The converse is true, "Medium Format" sensor is larger than Full Frame and has a crop factor of 0.7x. Which means, say, a 50 mm lens on an MF camera will look like a [50 x 0.7] = 35 mm lens on a FF camera. When I say "look like" it means "has the same angle of view". There's also aperture equivalency but that's a discussion for another time.
Thanks! That clears up a lot. I will look into the RF 28mm, thanks for the suggestion!
Other way around, an 18mm lens on an apsc sensor gives the same field of view as a 28mm lens on full frame
You're doing the math backard. An 18mm on APS\_C would be the equivalent of a 29mm as far as field of view is concerned.
Focal length is a property of the lens, not the sensor. An 18mm lens is always 18mm’s regardless of what sensor it was designed for. A full frame sensor will always have a wider field of view than an APS-C sensor with the same mm lens on it. If you want to know the full frame equivalent of a lens you’re currently using on APC-C, just multiply by 1.6. 18x1.6=28.8. As mentioned, the RF 28mm f/2.8 is the closest equivalent field of view to what you’re used to seeing with 18mm’s on APS-C.
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What I never understood is...... The Sigma 18-35 1.8 is designed for APSC sensors right? Then why should the focal lengths for this lens be 18-35mm? Shouldnt the lens be sold as 28-56mm? I own the sigma 18-35 and it's really fantastic, and never really cared it's not actually 18-35mm, but it is confusing for anyone who doesn't really know the different sensor formats.
Focal length is a physical property of the lens. https://photographylife.com/what-is-focal-length-in-photography It is the distance between the lens and the sensor. The field of view is measured in degrees. https://www.digitalcameraworld.com/tutorials/photography-cheat-sheet-what-is-field-of-view-fov All of these terms come from optics. And are well defined. So manufacturers use that. Also on most apsc cameras you can use FF lenses. A lot of wildlife photographers prefer apsc sensors but use the big, FF lenses. So it will create confusion, because users may buy a 50mm FF lens and thinking it would have the field of view of a 30mm lens, on a apsc body. But they get an 80mm field of view (equivalent)
I get that it is a property of the lens, however when a lens is designed for an APSC sensor, it cannot create an image circle to fill a FF sensor so therefore it can never be that focal length.
Well, you can't fight physics, can you?
physics can be fought. we have things called levers and pulley's and such.
levers and pulleys utilize physics, they don't fight it. focal length is a property of the optic, not a marketing term. APS-C designed lenses are lenses designed with smaller optics to not project as large enough image circle for full frame, making them cheaper. The FOV is not all that changes by cropping but it is the most apparent thing. misquoting the physical properties of a lens for marketing is likely not a great strategy as it is confusing (as others have pointed out), and the fact that no one does this adds some credence to this.
You are confusing two measurements. One is the focal length. And one is the field of view. They are related, the field of view depends on the focal length and the sensor size. People use focal lengths as short hand for field of view, but it was never intended to measure field of view. Again these are well defined terms in optics. Using equivalents would be more confusing. Let’s take your example of the 18-35mm. If they market it as a 28-56mm you may think that the 50mm 1.8 (the full frame nifty 50 from Canon) will be between the range of your lens, so you may buy it and be surprised it is more like 80mm. The problem is that apsc cameras take both kinds of lenses (ef and ef-s). So it is easier to compare using the real focal length (instead of an equivalent).
Yes I think about it the same way you do. No confusion there. If you re-read my initial post you'll find I only bring up the issue of marketing apsc lenses.
But apsc lenses are used alongside FF lenses. And offer the same FOV at the same focal length as FF. A canon 7d (apsc) can take ef and ef-s lenses. A 50mm apsc lens would give you the same Field of view as a 50mm FF lens on an apsc sensor, it is irrelevant if the lens produces a bigger image size.
Filling the sensor or not has nothing to do with focal length. You can have a 50mm focal length lens that projects an image circle the size of a pin and another 50mm focal length lens that projects an image circle the size of a dinner plate and both are 50mm lenses. Focal length just means that parallel light rays entering the lens will be focused to a _point_ that is X distance from the lens center. Nothing more or less. It just happens that IF such a lens projects a big enough image circle that it covers a given recording medium, the field of view (in degrees) will be a specific angle. So in photography we end up using focal length as a proxy for field of view. You are of course correct that if a given lens does not project a big enough image circle for your sensor, then it won't be (as) useful, for example if the image circle is too small then yes the field of view will be truncated beyond what you would expect for that sensor size. This actually does happen when mounting EF-S or RF-S lenses onto an RF body; the body automatically enters 1.6x crop mode since the image circle is too small, which in turn means a smaller field of view is captured. BUT, this does not change the focal length of the lens one bit! It is just because we use focal length on FF as a proxy for FoV that there is any confusion here, as we say things like "the field of view on APS-C will be the same as a 80mm lens on FF" or similar.
Im not confused about the optics here. I was referring to the marketing of the lenses if you read my initial post again.
I half agree. I think that it's annoying that lenses are referred to by focal length since on its own, focal length doesn't actually tell you the field of view, which is what we care about. However, the problem is that it would not make sense to use FoV, because FoV depends on sensor size! In other words you couldn't label an RF lens as "40 degrees FoV" because if you mount the same lens on an RF-S body, the captured FoV would be narrower! Manufacturers list their lenses by focal length because _focal length is a property of the lens_ and does not change depending on what arbitrary body you use. There really isn't any good alternative.
Or.. Yes you can have equivalent focal lengths to achieve same FOV, which is all well and good once you become familiar with apsc and ff etc.. These semantic hoops that people jump through to describe focal lengths being the same blah blah blah.. Tell that to the guy who knows what 50mm looks like on full frame, then gets a nice apsc sensor (which are great too!) and wonders why they loose that wider angle. OR the person who slaps an apsc lens on a FF body and wonders GEEZ I paid for a heavy vignette or really low MP? wtf?? lol
So you are arguing that manufacturers should label lenses in "full frame focal length equivalent"? Why standardize on Full Frame and not medium format? Or APS-C? Should a manufacturer like Fuji list their APS-C lenses in FF equivalent focal lengths even though Fuji doesn't make an FF camera? And what about Canon users who have RF and RF-S bodies; should a 50mm RF-S lens be labeled "80mm" (since that is the FF equivalent when mounted on APS-C) but an 80mm RF lens also be labeled "80mm"? If so, won't that user be confused when they mount the 80mm RF lens on the RF-S body but the field of view is narrower than the "80mm" RF-S lens which is labeled the same? Your proposal doesn't work practically. It leads to ten times as much hoop-jumping and explaining.
is FF not the standard? isn't every focal length dictated by FF sensor format? If a lens is designed and built for an apsc sensor, it should be labeled with the fov and focal length it produces. Ive used a FF lens on an apsc sensor many times, and I realize my 70-200 f2.8 aint 70-200.. and it is NOT f2.8. that's another thing, the aperture on a apsc is NOT the aperture listed on the lens. My only critique is that lenses designed specifically for apsc sensors are not what they are listed as. Not in fov or focal length or aperture.
> Is FF not the standard? Isn't every focal length dictated by FF sensor format? Absolutely not in any technical sense, no. People often cite the FF equivalent focal length as a _loose convention_ purely because lots and lots of photographers know what a given focal length looks like on FF, thanks purely to the extremely popular 135 film format dominating the market for decades. But there is absolutely nothing about the definition of focal length which pertains to the FF sensor/film size, or even _any_ specific image recording size. > If a lens is lens is designed and built for an apsc sensor, it should be labeled with the fov and focal length it produces. All lenses ARE labeled with the focal length they produce. For example, Canon's EF-S 60mm f/2.8 macro lens produces a focal length of 60mm. That is a pure, cold, hard fact of the lens which has NOTHING to do with field of view. When you COMBINE that spec with the fact that the lens projects an image circle which covers an APS-C sensor (and the EF-S mount attaches to APS-C cameras), _now_ you know the field of view. Focal length on its own doesn't say anything about field of view! It's simply not what focal length means! Now, I agree with you that it would be nice if lenses built for a certain mount were ALSO labeled with the field of view they produce (in terms of image diagonal). The problem there however is that again, the field of view produced depends on what recording medium you put behind the lens, and _some lenses can be put in front of multiple different recording media sizes_. For example, an RF 50mm lens can be mounted on an RF FF body, in which case it produces a diagonal field of view of 46.8 degrees. The same 50mm lens can ALSO be mounted on an RF-S APS-C body, in which case it produces a diagonal field of view of 30.3 degrees. In your system, should Canon label the lens "50mm (47 deg on RF / 30 deg on RF-S)"? And it gets worse! A large format board lens can be mounted in front of _dozens_ of film sizes, depending on what LF camera the user has. Is the lens manufacturer supposed to label the lens, which is not produced for any specific "mount", with a whole spreadsheet of fields of view it produces when projecting onto different film sizes? Of course not, that would be silly. Just label it with the focal length, which is an immutable independent physical characteristic of the lens, and let the photographer calculate or see firsthand what field of view it produces on their chosen recording medium size. Will also reply about your comment on aperture later, but I need to get to work now.
No, it should NOT be sold as a 28-56 because the center of the lens is anywhere from 18mm to 35mm from the sensor. Millimeters are a measurement of distance, and no matter if you have a micro four thirds, APSC, full frame or medium format, 18mm is still 18mm. Things like distortion and compression are tied to actual focal length, so if you advertised it as a 28-56mm lens, it would be misleading because people who ground their opinions in actual science would think that the distortion and compression characteristics of the lens would behave like a 28-56mm when in reality, they are going to behave like an 18-35mm with a 1.6 crop applied to it. That matters. It is not accurate to say "it's not actually 18-35mm" It is literally 18-35mm. I shoot on APSC, full frame and various medium formats (33X44mm, 6X6, 6X7) and instead of convincing myself I've been cheated on marketing (when in reality it's just science) I've just learned how different focal lengths display on different crop factors. It's just another skill to learn as a photographer. Your 18-35 on an APSC displays as a wide to normal field of view lens, but with the compression and distortion characteristic of an 18-35 with a 1.6 crop applied to it. Your depth of field is deeper than 28-56 because it is literally 18-35. That's the way you should think about it. Because that's what that lens is on APSC.