Is the listed focal length for an EF lens assuming it is on a full frame camera? And therefore an EF-S and EF lens of the same listed focal length would have differing fields of view on a crop sensor camera?
FSM Member 37 posts Joined Jul 2010 More info | Sep 05, 2010 11:32 | #1 Is the listed focal length for an EF lens assuming it is on a full frame camera? And therefore an EF-S and EF lens of the same listed focal length would have differing fields of view on a crop sensor camera? camera, lens, flash, etc
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rusty.jg Senior Member 855 posts Joined Mar 2009 Location: Cornwall, UK More info | Sep 05, 2010 11:36 | #2 FSM wrote in post #10853952  Is the listed focal length for an EF lens assuming it is on a full frame camera? And therefore an EF-S and EF lens of the same listed focal length would have differing fields of view on a crop sensor camera? As far as I understand it - not quite. A 50mm lens is a 50mm lens regardless of what "recording medium" you put behind it (crop,FF,film, etc). The only difference is *I think* is how big the image circle thrown by the lens is - which dictates how big a sensor you can get away with. to be OR NOT to be = 1 (which is "to be" so that one's cleared up at last
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ImRaptor Goldmember  1,448 posts Joined Mar 2008 Location: Humboldt, SK Canada More info | Sep 05, 2010 11:40 | #3 17mm on the 17-40mm EF will look exactly the same as the 17mm on the 17-55mm EF-s when used on an APS-C sensor based camera. http://imraptor.deviantart.com/
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edrader "I am not the final word"  More info | Sep 05, 2010 11:42 | #4 rusty.jg wrote in post #10853985 As far as I understand it - not quite. A 50mm lens is a 50mm lens regardless of what "recording medium" you put behind it (crop,FF,film, etc). The only difference is *I think* is how big the image circle thrown by the lens is - which dictates how big a sensor you can get away with. Someone please correct me if I'm wrong. first i have to figure out what the hell you are talking about http://instagram.com/edraderphotography/
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SkipD Cream of the Crop  20,476 posts Likes: 165 Joined Dec 2002 Location: Southeastern WI, USA More info | Sep 05, 2010 11:48 | #5 FSM wrote in post #10853952 Is the listed focal length for an EF lens assuming it is on a full frame camera? And therefore an EF-S and EF lens of the same listed focal length would have differing fields of view on a crop sensor camera? Focal length of a lens has absolutely nothing to do with the camera it may be attached to.
For the OP - the following should help you understand the "crop factor" issues a bit better: The "crop factor" is a reference number that relates to the difference in film or sensor size (known as the camera's "format") between two cameras like the Canon 50D and a 35mm film (or a so-called "full-frame" digital) camera. Let me list the facts: 35mm film cameras and so-called "full frame" DSLRs have a film frame or sensor size of approximately 24mm X 36mm, while the Canon 50D has an APS-C sized sensor, measuring approximately 14.9mm X 22.3mm. The other Canon APS-C format cameras - starting with the D30 in the year 2000 and progressing through all of the "digital Rebel" xxxD series, the xxD series, and today's 7D - all have sensors that are sized similar to that in the 50D. When camera manufacturers started designing digital SLRs (DSLRs), they decided that the DSLR bodies should be about the same physical size and configuration as their 35mm film SLRs. For that reason, they concluded that they could use the line of lenses they already had for their 35mm SLRs on the new DSLRs. All lenses designed for 35mm cameras project an image circle onto the film that covers a 24mm X 36mm rectangle. The 35mm camera records the portion of that image circle that is defined by the opening behind the shutter for the film (24mm X 36mm in size). A digital SLR with an APS-C sized sensor only records the smaller area (approximately 15mm X 22mm) of the image circle projected by the same lens. When you put a 100mm lens on a 35mm film camera and make a photograph, then put the same lens on a DSLR such as the Canon 50D and make a similar photograph - same subject, same position for the camera, and same focal length - and then enlarge both photographs to the same size print (4 X 6 inches, for example), it will appear as though the photo from the Canon 50D was taken with a longer lens. That is because the image recorded by the Canon 50D was of a SMALLER PORTION of the image circle projected by the lens - cropped, if you will - compared to the image recorded by the 35mm camera. The special lenses for the Canon 50D (and other Canon APS-C cameras starting with the 300D - the first Digital Rebel) are called the EF-S series. These project a smaller image circle, making the lenses less expensive to design and produce in wide-angle and extreme wide-angle formats. The EF-S lenses also project deeper into the camera than the EF specification allows (the "S" referring to "Short back focus), allowing for less expensive wide-angle lens designs. However, an EF-S lens set to 40mm will produce the exact same image as an EF lens set to 40mm if both lenses are used on the same APS-C format body and both lenses are focused at "infinity". Focal length is focal length, period. Now to the primary point that I want to make: NOTHING about lens EVER CHANGES when you put it on different format cameras. Focal length never changes. Aperture range never changes. The only thing that would change is the apparent field of view, and that change is not a function of the lens but it is a function of the size of the sensor or film that will record the image. The "crop factor" calculation for "35mm equivalent focal length" has only one valid use. That is for comparing lenses used on two different format cameras. Here's one common example: Joe took a photo of Mount Rushmore with a 35mm camera from a particular place using a 200mm lens. You want to replicate that photo with your Canon 50D. What focal length do you need to do that from the same location that he took his photo? Divide the 200mm by 1.6 and you get the answer - 125mm. Here's another popular example: Mary Sue has been using a Canon SX120 IS point-n-shoot camera and is wanting to use a Canon 50D DSLR. She is, of course, interested in what focal lengths she would need to keep the versatility of the SX120 camera's 10X super-zoom lens. The SX120 lens is actually a 6.0mm to 60.0mm lens, but the advertising also shows the "35mm equivalent" focal length range as 36mm to 360mm. To know the focal lengths needed for the 50D, merely divide the "35mm equivalent" values by 1.6. In other words, Mary Sue would need 22.5mm on the short end and 225mm on the long end for the 50D to have the same field (angle) of view coverage as her SX120 IS camera. The "crop factor" is NOTHING MORE than a REFERENCE between the two camera formats that lets you compare the field of view of particular focal lengths between the two formats. The "crop factor" (as related to using lenses essentially designed for 35mm SLR cameras) is always given assuming that the 35mm format (24mm X 36mm) is the reference master. Something to realize, though, is that the 35mm film format is not, never has been, and never will be the master" format against which all other camera formats are referenced. It is simply the format of the cameras that have also evolved into today's commonly used digital SLRs. Skip Douglas
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rusty.jg Senior Member 855 posts Joined Mar 2009 Location: Cornwall, UK More info | Sep 05, 2010 11:50 | #6 ed rader wrote in post #10854025 first i have to figure out what the hell you are talking about  !ed rader If you do, can you let me know! It might be handy... to be OR NOT to be = 1 (which is "to be" so that one's cleared up at last
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sandpiper Cream of the Crop  More info | Sep 05, 2010 11:51 | #7 FSM wrote in post #10853952 therefore an EF-S and EF lens of the same listed focal length would have differing fields of view on a crop sensor camera? No, focal length is not dependent on format, the only difference between EF and EF-S lenses is that EF-S lenses do not have as big an opening at the back, so project a smaller image circle that covers the smaller crop sensor, but will not cover a FF sensor. The actual image (from a given focal length) projected will be identical, over the area of the crop sensor, regardless of whether the lens is an EF or EF-S of the same focal length.
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Sep 05, 2010 13:07 | #8 Very informative post, Skip.
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DAMphyne "the more I post, the less accurate..."  More info | Sep 05, 2010 13:24 | #9 Usually the problem with using a long focal length for portraits is the distance you need to be from the subject to get them in the frame. You change perspective because you have to move further away from the subject. David
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MrLA Senior Member  727 posts Likes: 2 Joined Jun 2007 More info | Sep 05, 2010 13:25 | #10 when taking picture from the same distance, putting a 50mm lens on a cropped(1.6x) body has the same field of view as a 80mm lens on on a full-frame camera. it's like u put a 1.6x teleconversion on a lens. some say 50mm is always 50mm that's what the software reads but not from your field of view. Body: Canon 5Dc, (Coming soon <<<6Dc, maybe I shall wait for 6Diic with TouchScreen!).
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ImRaptor Goldmember 1,448 posts Joined Mar 2008 Location: Humboldt, SK Canada More info | Sep 05, 2010 13:25 | #11 Perspective only changes with your positioning. http://imraptor.deviantart.com/
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macroimage Goldmember 2,169 posts Likes: 2 Joined Aug 2007 More info | Sep 05, 2010 13:26 | #12 IdiotsAbound wrote in post #10854352 Example, my Sigma 105mm EX 2.8 Macro is an excellent portrait lense on a full frame. But put it on a 1.6x crop camera (My XSi) and it effectively becomes a 168mm lense. Does the perspective change with the 1.6 crop factor or stay the same? I know a 160mm lense is way over reaching on a full frame for portraits due to perspective.
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SkipD Cream of the Crop 20,476 posts Likes: 165 Joined Dec 2002 Location: Southeastern WI, USA More info | Sep 05, 2010 13:43 | #13 IdiotsAbound wrote in post #10854352 Example, my Sigma 105mm EX 2.8 Macro is an excellent portrait lense on a full frame. But put it on a 1.6x crop camera (My XSi) and it effectively becomes a 168mm lense. Your 105mm lens is ALWAYS a 105mm lens and does not effectively become anything else. IdiotsAbound wrote in post #10854352 I have a question regarding the focal length, crop cameras and perspective. Does the perspective change on a crop camera as well? Example, my Sigma 105mm EX 2.8 Macro is an excellent portrait lense on a full frame. But put it on a 1.6x crop camera (My XSi) and it effectively becomes a 168mm lense. Does the perspective change with the 1.6 crop factor or stay the same? I know a 160mm lense is way over reaching on a full frame for portraits due to perspective. Regardless of the popular myths, perspective - defined as the relative sizes of objects in the scene at different distances from the camera - has absolutely nothing to do with focal length per se. It is affected purely by the distances between the camera and the various elements in the scene. Skip Douglas
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Sep 05, 2010 14:13 | #14 Thank you for the reply guys. It's a question that's been bugging me for a while as this is one of my favorite lenses. The other 2 I have are the EF-S 18-55 IS (walk around lense) and the lowly 75-300 USM III which I rarely use until I can afford better.
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richardfox Goldmember  1,883 posts Joined Oct 2009 Location: Bellbrook, Ohio, USA More info | Sep 05, 2010 17:41 | #15 SkipD wrote in post #10854058 Focal length of a lens has absolutely nothing to do with the camera it may be attached to. All photographic lenses (at least those made by Canon, Nikon, and other reputable manufacturers) are marked with their actual focal lengths. If you compared the images you would make with an APS-C format camera such as a 50D using an EF 50mm lens and an EF-S lens set to 50mm, you would find that both images would be the same. There are a few details to understand, though, which could make this test seem invalid if you didn't understand them.
For the OP - the following should help you understand the "crop factor" issues a bit better: The "crop factor" is a reference number that relates to the difference in film or sensor size (known as the camera's "format") between two cameras like the Canon 50D and a 35mm film (or a so-called "full-frame" digital) camera. Let me list the facts: 35mm film cameras and so-called "full frame" DSLRs have a film frame or sensor size of approximately 24mm X 36mm, while the Canon 50D has an APS-C sized sensor, measuring approximately 14.9mm X 22.3mm. The other Canon APS-C format cameras - starting with the D30 in the year 2000 and progressing through all of the "digital Rebel" xxxD series, the xxD series, and today's 7D - all have sensors that are sized similar to that in the 50D. When camera manufacturers started designing digital SLRs (DSLRs), they decided that the DSLR bodies should be about the same physical size and configuration as their 35mm film SLRs. For that reason, they concluded that they could use the line of lenses they already had for their 35mm SLRs on the new DSLRs. All lenses designed for 35mm cameras project an image circle onto the film that covers a 24mm X 36mm rectangle. The 35mm camera records the portion of that image circle that is defined by the opening behind the shutter for the film (24mm X 36mm in size). A digital SLR with an APS-C sized sensor only records the smaller area (approximately 15mm X 22mm) of the image circle projected by the same lens. When you put a 100mm lens on a 35mm film camera and make a photograph, then put the same lens on a DSLR such as the Canon 50D and make a similar photograph - same subject, same position for the camera, and same focal length - and then enlarge both photographs to the same size print (4 X 6 inches, for example), it will appear as though the photo from the Canon 50D was taken with a longer lens. That is because the image recorded by the Canon 50D was of a SMALLER PORTION of the image circle projected by the lens - cropped, if you will - compared to the image recorded by the 35mm camera. The special lenses for the Canon 50D (and other Canon APS-C cameras starting with the 300D - the first Digital Rebel) are called the EF-S series. These project a smaller image circle, making the lenses less expensive to design and produce in wide-angle and extreme wide-angle formats. The EF-S lenses also project deeper into the camera than the EF specification allows (the "S" referring to "Short back focus), allowing for less expensive wide-angle lens designs. However, an EF-S lens set to 40mm will produce the exact same image as an EF lens set to 40mm if both lenses are used on the same APS-C format body and both lenses are focused at "infinity". Focal length is focal length, period. Now to the primary point that I want to make: NOTHING about lens EVER CHANGES when you put it on different format cameras. Focal length never changes. Aperture range never changes. The only thing that would change is the apparent field of view, and that change is not a function of the lens but it is a function of the size of the sensor or film that will record the image. The "crop factor" calculation for "35mm equivalent focal length" has only one valid use. That is for comparing lenses used on two different format cameras. Here's one common example: Joe took a photo of Mount Rushmore with a 35mm camera from a particular place using a 200mm lens. You want to replicate that photo with your Canon 50D. What focal length do you need to do that from the same location that he took his photo? Divide the 200mm by 1.6 and you get the answer - 125mm. Here's another popular example: Mary Sue has been using a Canon SX120 IS point-n-shoot camera and is wanting to use a Canon 50D DSLR. She is, of course, interested in what focal lengths she would need to keep the versatility of the SX120 camera's 10X super-zoom lens. The SX120 lens is actually a 6.0mm to 60.0mm lens, but the advertising also shows the "35mm equivalent" focal length range as 36mm to 360mm. To know the focal lengths needed for the 50D, merely divide the "35mm equivalent" values by 1.6. In other words, Mary Sue would need 22.5mm on the short end and 225mm on the long end for the 50D to have the same field (angle) of view coverage as her SX120 IS camera. The "crop factor" is NOTHING MORE than a REFERENCE between the two camera formats that lets you compare the field of view of particular focal lengths between the two formats. The "crop factor" (as related to using lenses essentially designed for 35mm SLR cameras) is always given assuming that the 35mm format (24mm X 36mm) is the reference master. Something to realize, though, is that the 35mm film format is not, never has been, and never will be the master" format against which all other camera formats are referenced. It is simply the format of the cameras that have also evolved into today's commonly used digital SLRs. Your signature id "learning all the time"? What could you possibly learn that you don't ALREADY KNOW?!! There are a few people on this board that have incredible levels of knowledge. You sir, are one! Kudos to your explanation on this topic. Amazing level of knowledge! Canon 50D gripped, EF 50/1.8, EF-S 10-22, 17-40L, 24-105L, 70-200 f/2.8L, 100/2.8 macro, 100-400L, 300 2.8L, Canon 500 f8 mirror with chipped EF mount, 580EX, 1.4x and 2x Canon teleconverters, Canon EF Life-Size converter.
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