The first dslr's all had APS-C sensors. Since then the big manufacturers (Canon, Nikon, Sony, Panasonic, Pentax) have developed "full frame" sensors to match (roughly) the size of old 35mm frames found in film cameras. Lenses were designed for 35mm (full frame) at first, then subsequently designed for APS-C.
Here is my gripe; APS-C lenses advertised as "equivalent to" whatever their multiplier is for full frame sensors (1.6, etc) in terms of field of view. For example:
Sigma 18-50mm = 27-75mm (35mm equivalent)
Sony 11mm = 16.5mm (35mm equivalent)
Fuji 23mm = 35mm (35mm equivalent)
Viltrox 13mm = 20mm (35mm equivalent).
I understand that these are field of view numbers, but why not advertise or describe the lens as what it will truly capture images as? If it's really a 27-75mm field of view lens, why advertise it as an 18-50mm lens? If the field of view is 20mm, why bother stamping on it "13mm"?
snegron7 wrote:
I understand that these are field of view numbers, but why not advertise or describe the lens as what it will truly capture images as? If it's really a 27-75mm field of view lens, why advertise it as an 18-50mm lens? If the field of view is 20mm, why bother stamping on it "13mm"?
It's probably for legal reasons that mm has to be in mm and equivalent sometimes in parens.
I'd rather know the actual focal length, angle of view, and the number of pixels/radian or pixels/mrad.
Unfortunately moist users don't like math, but anyone versed in photography should be able to determine how the values affect them.
In the 20th century we were doing equivalents all the time, but between various film formats. We didn't have software to determine field of view with arctan, but who did not have the FOV formula in their programmable calculator back in the day.
I think a bigger problem is manufactures just rounding up the lens focal length, sometimes being very generous. For example the Sony 200-600 really does not go to 600, but more like 550.
chez wrote:
I think a bigger problem is manufactures just rounding up the lens focal length, sometimes being very generous.
Tele lenses typically are shorter than labeled on the long end, but wide-angle lenses are typically longer than labeled. And of course the f numbers are usually not representive of light transmission, hence the t numbers on the cine lenses.
Until the 1980s the Japan Camera Inspection Institute had requirements for accuracy of apertures, focal lengths, etc. I'm sure some folks remember the oval JCII stickers.
You can use "full frame" lenses on smaller format cameras and vice versa. An 18mm lens has the same field of view regardless of what camera it is attached to. The difference is how much of that projected image the camera records. So even marking FOV angles on a lens would be confusing because you're still cropping the image on a smaller sensor. Focal length is focal length. Period.
It is up to the end user to understand what "18mm" or "50mm" means relative to the camera format they are using.
The focal length it’s not the field of view, FOV can be classified as horizontal vertical and diagonal, so that would make it very confusing to talk about, in fact while most people (with an interest in photography) know how images from a 35mm look like they wouldn’t be able to tell you the FOV of a 35mm prime.
The other reason is that the main brands (sony, canon and nikon) have a common lens mount for full frame and aps-c. You can use a 16mm full frame lens on an aps-c body, would you then advertise it as a 24mm or as 16mm?
As you see using the actual focal length it’s more honest and easier.
snegron7 wrote:
The first dslr's all had APS-C sensors. Since then the big manufacturers (Canon, Nikon, Sony, Panasonic, Pentax) have developed "full frame" sensors to match (roughly) the size of old 35mm frames found in film cameras. Lenses were designed for 35mm (full frame) at first, then subsequently designed for APS-C.
Here is my gripe; APS-C lenses advertised as "equivalent to" whatever their multiplier is for full frame sensors (1.6, etc) in terms of field of view. For example:
Sigma 18-50mm = 27-75mm (35mm equivalent)
Sony 11mm = 16.5mm (35mm equivalent)
Fuji 23mm = 35mm (35mm equivalent)
Viltrox 13mm = 20mm (35mm equivalent).
I understand that these are field of view numbers, but why not advertise or describe the lens as what it will truly capture images as? If it's really a 27-75mm field of view lens, why advertise it as an 18-50mm lens? If the field of view is 20mm, why bother stamping on it "13mm"?
The compact cameras of the 2000s always used the EFL. My Olympus C-7070 was advertised as having a 27-110mm lens, not a 5.7-22.9mm lens. Beginner camera, consumer level, not as advanced or professional, so EFL is less confusing.
With more advanced/pro cameras like m4/3, APS-C, FF, MF, they expect people to already know the difference. No need to emphasize the EFL as much, which actually might be confusing or even deceptive for systems with both APS-C and FF.
Probably some of it is marketing too. Companies want everyone to buy new cameras, new lenses, and part of that means encouraging upgrading to FF. Emphasizing the different focal lengths for APS-C vs. FF helps to remind people that APS-C sucks and FF is the way to go.
In the case of m4/3, different focal lengths helps to remind people that m4/3 is different. Again, marketing.
snegron7 wrote:
The first dslr's all had APS-C sensors. Since then the big manufacturers (Canon, Nikon, Sony, Panasonic, Pentax) have developed "full frame" sensors to match (roughly) the size of old 35mm frames found in film cameras. Lenses were designed for 35mm (full frame) at first, then subsequently designed for APS-C.
Here is my gripe; APS-C lenses advertised as "equivalent to" whatever their multiplier is for full frame sensors (1.6, etc) in terms of field of view. For example:
Sigma 18-50mm = 27-75mm (35mm equivalent)
Sony 11mm = 16.5mm (35mm equivalent)
Fuji 23mm = 35mm (35mm equivalent)
Viltrox 13mm = 20mm (35mm equivalent).
I understand that these are field of view numbers, but why not advertise or describe the lens as what it will truly capture images as? If it's really a 27-75mm field of view lens, why advertise it as an 18-50mm lens? If the field of view is 20mm, why bother stamping on it "13mm"?
Well, for one, since we don't live in a 2-dimensional world, the field of view isn't actually equivalent. Sure, if you only considered the X and Y axes they would be, but using a smaller sensor doesn't negate the fact that a 23mm focal length is still a 23mm focal length.
For example, shoot a subject with a 23mm lens on a crop sensor. Then shoot the same subject with a 35mm lens on a full-frame body, while having the subject occupy the same amount of the frame. The 23mm lens on the crop sensor camera will have more of the background in the image and less bokeh. Whether that's a good thing or a bad thing depends on what you're trying to achieve, of course.
Even though the 23mm lens is considered to be a 35mm "equivalent," it's not - it's still a 23mm focal length.
doady wrote:
The compact cameras of the 2000s always used the EFL. My Olympus C-7070 was advertised as having a 27-110mm lens, not a 5.7-22.9mm lens. Beginner camera, consumer level, not as advanced or professional, so EFL is less confusing.
Per DPreview the actual focal length is on the lens.
Yeah, I know. Every compact camera has the actual focal length printed on the body somewhere.
I was referring to marketing. It was advertised as a "Wide Zoom" lens, it is in the name of the camera, it is one of the defining features of the camera, wider than other compact cameras at that time. But the 5.7mm focal length is not mentioned anywhere in the announcement, nor is it listed in specs on the cameras DPReview page. The specs only show the EFL, not the actual focal length.
Ok, today I finally did a hands-on experiment regarding "field of view vs focal length". The results were exactly as I suspected.
I used a Canon EF 17-40mm f4.0L on my two cameras; an R6 and a 7dmk2.
I captured the same image of the same subject at the same distance at 17mm with the full frame R6 and the APS-C sensor 7dmk2.
There was much, much more items showing on the R6 image vs the 7dmk2 image. The R6 image looked like a true wide angle image at 17mm, whereas the image of the 7dmk2 at 17mm looked like a 28mm image.
In other words, if you are taking a group shot of 15 people with a full frame wide angle lens, you would have to stand several feet back in order to fit all of them in the frame if you are using an APS-C sensor camera vs a full frame camera.
This is critical for indoor shots where space is limited. You can capture more of the room with a full frame camera than you can with an APS-C camera using the same lens.
So, the reality is that a full frame 17-40mm lens on an APS-C camera is in fact a 27-64mm lens when it comes to the image you captured. In other words, 17mm full frame shows like a 27mm on an APS-C camera.
On a side note, I tried my Canon EF-S 17-55mm f2.8 on both my R6 and 7dmk2. At 17mm the image looks like a true 17mm on the 7dmk2, whereas on the R6 it looks like a 25mm or 27mm image (looks cropped on the R6, but looks like a true wide angle 17mm on the 7dmk2)!
chez wrote:
I think a bigger problem is manufactures just rounding up the lens focal length, sometimes being very generous. For example the Sony 200-600 really does not go to 600, but more like 550.
The 200-600 does go to 600, at infinity, which is where focal length is measured. Due to it's optical design it has significant *focus breathing* at shorter distances and so covers a wider field of view at close distances than it does at long focus distances. It's not un common. All lens design involved compromises, expecially in zooms.
snegron7 wrote:
The first dslr's all had APS-C sensors. Since then the big manufacturers (Canon, Nikon, Sony, Panasonic, Pentax) have developed "full frame" sensors to match (roughly) the size of old 35mm frames found in film cameras. Lenses were designed for 35mm (full frame) at first, then subsequently designed for APS-C.
Here is my gripe; APS-C lenses advertised as "equivalent to" whatever their multiplier is for full frame sensors (1.6, etc) in terms of field of view. For example:
Sigma 18-50mm = 27-75mm (35mm equivalent)
Sony 11mm = 16.5mm (35mm equivalent)
Fuji 23mm = 35mm (35mm equivalent)
Viltrox 13mm = 20mm (35mm equivalent).
I understand that these are field of view numbers, but why not advertise or describe the lens as what it will truly capture images as? If it's really a 27-75mm field of view lens, why advertise it as an 18-50mm lens? If the field of view is 20mm, why bother stamping on it "13mm"?
Focal length is measured in mm. It's a function of the lens design and describes the length of the light path through a lens (heavily simplified description). This will be independant of the sensor size.
Image circle describes the size of the image circle projected onto the sensor. Some lenses have an image circle big enough to cover an APSC sensor. Some are large enough to cover larger sensors like 24x36 (poorly named *full frame*) and medium format. Some project smaller image circles like m43 or smart phones. As an example your wide angle efs zoom doesn't project a big enough image circle to cover a 24x36mm sensor. Your full frame camera knows this and will automatically use a smaller part of the sensor. ie: you'll use an APSC part of a full frame sensor. If you don't your corners will be black.
Field of view (angle of view) is described in degrees. It describes the horizontal, vertical and diagonal field of view when you project an image from a certain focal length onto a sensor of a certain size. Because you can project a 50mm focal length lens onto different sensor sizes, each different sensor size will *see* a different field of view. So we have a system that shows trys to represent a standard.
Somewhere, at some point someone decided that the 24x36 sensor format would be the *standard* and when we talk about other sensor sizes people will add a *what this would be on 24x36 (full frame)* so we can quickly get an idea of how a lens on different sized sensors compares for angle of view.
So if you project a 20mm lens onto a 24x36mm sensor the angle of view is 94 degrees diagonal. To get the same angle of view on an APSC sensor you'll need a 14mm lens (approximately). So a Canon efs 14mm lens has an equivalent of 20mm lens (to get the same angle of view on the 24x36mm sensor).
Crop factor, is the amount you multiply by to get to the *standard* we use. That's 2.0 for m43, 1.5 for APSC except Canon, 1.6 for Canon 1.0 for *full frame* and 0.8 for mini medium format (33x44). Using this I can reasonably quickly compare the angle of view from different formats. For example if I want the same angle of view as my 20mm lens on 24x36 then I need a 10mm m43 lens, a 14mm APSC lens or a 25mm mini medium format lens.
The focal length doesn't change. A 20mm is a 20mm is a 20mm. Equivalence is just a way to compare a lens' angle of view on different systems.
flash wrote:
The 200-600 does go to 600, at infinity, which is where focal length is measured. Due to it's optical design it has significant *focus breathing* at shorter distances and so covers a wider field of view at close distances than it does at long focus distances. It's not un common. All lens design involved compromises, expecially in zooms.
Gordon
Being common does not mean it’s still not misleading.
Now we have the "computational" lenses that exhibit severe distortion and nowhere near the 43mm diagonal coverage. One can argue that the focal length variation with r and the image circle are so far out of whack to be even more misleading than just the typical FL errors. Edge illumination falloff combined with bogus f/numbers also seem to be worse than ever. All these shenanigans are managing to be legal under fit for use. The old FLs were ±5% IIRC and more than a certain amount of distortion would be a fisheye. Fortunately we have many testers out there to provide info so that the user can decide.
chez wrote:
Being common does not mean it’s still not misleading.
I agree it’s far from ideal. I’m just not sure how the system could label every lens that focus breathes with it’s deviance at closer distances. That’d be more than half the lenses currently made. Fortunately it’s pretty easy to find this information from reviewers etc.
The only two systems I’m aware of where the actual and correct focal length is listed is on the barrel of some Leica M lenses and in the charts for Hasselblad glass. These are done to 1/10th of a mm. For example the Summilux 50 M is actually a 52.3mm lens at infinity and this is marked with a code on each lens. It’s slightly wider than a 50 at minimum FL but Leica doesn’t list this. So the figures are only accurate at infinity due to breathing.
The old FLs were ±5% IIRC and more than a certain amount of distortion would be a fisheye. Fortunately we have many testers out there to provide info so that the user can decide.