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<blockquote data-quote="Bob Blaylock" data-source="post: 229387" data-attributes="member: 16749"><p>The focal length is real. The confusion has to do with the size of the frame, be it a frame of stone-aged 35mm film, some other format of film, or the sensor in a digital camera.</p><p></p><p> For a very long time, 35mm was the very most common film format, with a standard frame size roughly 36mm by 24mm. A lens with a 50mm focal length was considered the “standard” size lens to use with a 35mm camera, because it yields an angle of view that is roughly comparable to that of the human eye.</p><p></p><p> FX-format digital cameras use a sensor that is about the same size as a standard 35mm film frame, so a lens used on an FX camera will have the same field of view as that same lens on a 35mm film camera.</p><p></p><p> DX-format cameras use a sensor that is smaller than a 35mm film frame. The same lens used on a DX-format camera will have a narrower angle of view, than on an FX-format camera.</p><p></p><p> An FX-format sensor is roughly 1.5 times the size of a DX-format sensor. This 1.5 is the “crop factor” you've heard about. Since a DX-format sensor is 1.5 times smaller than an FX-format sensor, you need a lens with a focal length 1.5 times shorter to get the same angle of view on a DX-format camera compared to an FX-format camera. While 50mm is considered the “standard” focal length for a lens on an FX-format camera, the “standard” lens for a DX-format camera would be around 35mm.</p><p></p><p> See also: <ul> <li data-xf-list-type="ul"><a href="https://en.wikipedia.org/wiki/Crop_factor" target="_blank">https://en.wikipedia.org/wiki/Crop_factor</a></li> <li data-xf-list-type="ul"><a href="https://en.wikipedia.org/wiki/Image_sensor_format" target="_blank">https://en.wikipedia.org/wiki/Image_sensor_format</a></li> </ul><p></p><p>[ATTACH]62115[/ATTACH] [ATTACH]62116[/ATTACH]</p><p>[ATTACH]62114[/ATTACH]</p><p></p><p> The only real difference between a DX lens and an FX lens is that an FX lens is expected to be used on a FX-format camera, or a full-sized 35mm film camera, and so needs to project an image that will cover a full 35mm-sized frame; while a DX-lens is expected to only be used on a DX-format camera, and is only expected to cover a DX-sized frame. You can use an FX lens on a DX camera with no issues, but if you use a DX lens on an FX camera, it won't cover the entire frame.</p></blockquote><p></p>
[QUOTE="Bob Blaylock, post: 229387, member: 16749"] The focal length is real. The confusion has to do with the size of the frame, be it a frame of stone-aged 35mm film, some other format of film, or the sensor in a digital camera. For a very long time, 35mm was the very most common film format, with a standard frame size roughly 36mm by 24mm. A lens with a 50mm focal length was considered the “standard” size lens to use with a 35mm camera, because it yields an angle of view that is roughly comparable to that of the human eye. FX-format digital cameras use a sensor that is about the same size as a standard 35mm film frame, so a lens used on an FX camera will have the same field of view as that same lens on a 35mm film camera. DX-format cameras use a sensor that is smaller than a 35mm film frame. The same lens used on a DX-format camera will have a narrower angle of view, than on an FX-format camera. An FX-format sensor is roughly 1.5 times the size of a DX-format sensor. This 1.5 is the “crop factor” you've heard about. Since a DX-format sensor is 1.5 times smaller than an FX-format sensor, you need a lens with a focal length 1.5 times shorter to get the same angle of view on a DX-format camera compared to an FX-format camera. While 50mm is considered the “standard” focal length for a lens on an FX-format camera, the “standard” lens for a DX-format camera would be around 35mm. See also:[list][*][url]https://en.wikipedia.org/wiki/Crop_factor[/url] [*][url]https://en.wikipedia.org/wiki/Image_sensor_format[/url][/list] [ATTACH=CONFIG]62115._xfImport[/ATTACH] [ATTACH=CONFIG]62116._xfImport[/ATTACH] [ATTACH=CONFIG]62114._xfImport[/ATTACH] The only real difference between a DX lens and an FX lens is that an FX lens is expected to be used on a FX-format camera, or a full-sized 35mm film camera, and so needs to project an image that will cover a full 35mm-sized frame; while a DX-lens is expected to only be used on a DX-format camera, and is only expected to cover a DX-sized frame. You can use an FX lens on a DX camera with no issues, but if you use a DX lens on an FX camera, it won't cover the entire frame. [/QUOTE]
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