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<blockquote data-quote="WayneF" data-source="post: 649841" data-attributes="member: 12496">Right.&nbsp; The way this term Equivalent Focal Length is used (e.g., the DX&nbsp; 1.5 crop factor, and 1.5x longer Equivalent focal length) is that this&nbsp; Equivalence only applies to the FX sensor, and NOT at all to the DX camera. &nbsp;The lens is what it is, it does the same thing on DX or FX. The focal length is always what is printed on the lens body. The DX camera sees the field of view as defined by the size of the&nbsp; sensor.&nbsp; A smaller field of view if a cropped smaller sensor. However,&nbsp; DX Crop 1.5 means that the FX sensor is 1.5x larger, and the DX sensor&nbsp; is 2/3 the size of FX (1/1.5 = 2/3).&nbsp; So the field of view of FX (with&nbsp; this same lens) is 1.5x larger than as seen on DX (only because the DX&nbsp; sensor is cropped smaller).&nbsp; The meaning of Equivalence is that the FX&nbsp; sensor with a lens 1.5x longer would then see the same smaller field of&nbsp; view as DX with the original lens. This &quot;Equivalent Focal Length lens&quot;&nbsp; is mounted on the FX body (for the comparison).&nbsp;&nbsp; Not when mounted on&nbsp; the DX body. This real focal length on the DX sensor has the same field&nbsp; of view as the Equivalent (1.5x longer) focal length on the FX body.If we are using the new fangled DX sensor (compared to decades of 35 mm&nbsp; film use), we are not at that moment much interested in what FX might&nbsp; do.&nbsp; However, the big exception is that if our experience knows exactly&nbsp; what focal length X does on full frame (from years of 35 mm film), then&nbsp; we already know what X/1.5 mm focal length will do on DX.&nbsp; My own notion&nbsp; is that this experience is the ONLY reason to imagine comparing them (and it would seem very valuable then).&nbsp; But if we are already standing there holding the DX camera with this&nbsp; lens on it, then Equivalent Focal Length (on FX) is not of much interest&nbsp; to us. The lens does only what it does&nbsp; and can do, on either body (it is only&nbsp; the sensor sizes that vary the field of view).&nbsp; What we seem to need is&nbsp; more clear words to describe&nbsp; the effect of the smaller sensor.&nbsp;&nbsp; To&nbsp; describe the actual smaller view instead wording it so much in terms of&nbsp; what another sensor might do.&nbsp;&nbsp; Crop seems such a word, but 1.5 is in&nbsp; terms of the full frame sensor. And Equivalent is in terms of the full&nbsp; frame sensor.&nbsp; We have boxed ourselves in.&nbsp; It would seem more clear&nbsp; with DX described as a 2/3 size sensor instead of a 1.5x crop which&nbsp; describes larger FX instead.But the crop factor thing does seem to come clear when we actually try&nbsp; to visualize the smaller DX sensor cropping the field of view of the&nbsp; lens to be smaller...&nbsp; cropped.&nbsp; &nbsp; And when that understanding becomes&nbsp; clear, there would seem to be little problem with it. But we do have to&nbsp; understand to understand.</blockquote>

[QUOTE="WayneF, post: 649841, member: 12496"] Right. The way this term Equivalent Focal Length is used (e.g., the DX 1.5 crop factor, and 1.5x longer Equivalent focal length) is that this Equivalence only applies to the[B] FX[/B] sensor, and NOT at all to the DX camera. The lens is what it is, it does the same thing on DX or FX. The focal length is always what is printed on the lens body. The DX camera sees the field of view as defined by the size of the sensor. A smaller field of view if a cropped smaller sensor. However, DX Crop 1.5 means that the FX sensor is 1.5x larger, and the DX sensor is 2/3 the size of FX (1/1.5 = 2/3). So the field of view of FX (with this same lens) is 1.5x larger than as seen on DX (only because the DX sensor is cropped smaller). The meaning of Equivalence is that the [B]FX[/B] sensor with a lens 1.5x longer would then see the same smaller field of view as DX with the original lens. This "Equivalent Focal Length lens" is mounted on the FX body (for the comparison). Not when mounted on the DX body. This real focal length on the DX sensor has the same field of view as the Equivalent (1.5x longer) focal length on the FX body. If we are using the new fangled DX sensor (compared to decades of 35 mm film use), we are not at that moment much interested in what FX might do. However, the big exception is that if our experience knows exactly what focal length X does on full frame (from years of 35 mm film), then we already know what X/1.5 mm focal length will do on DX. My own notion is that this experience is the ONLY reason to imagine comparing them (and it would seem very valuable then). But if we are already standing there holding the DX camera with this lens on it, then Equivalent Focal Length (on FX) is not of much interest to us. The lens does only what it does and can do, on either body (it is only the sensor sizes that vary the field of view). What we seem to need is more clear words to describe the effect of the smaller sensor. To describe the actual smaller view instead wording it so much in terms of what another sensor might do. Crop seems such a word, but 1.5 is in terms of the full frame sensor. And Equivalent is in terms of the full frame sensor. We have boxed ourselves in. It would seem more clear with DX described as a 2/3 size sensor instead of a 1.5x crop which describes larger FX instead. But the crop factor thing does seem to come clear when we actually try to visualize the smaller DX sensor cropping the field of view of the lens to be smaller... cropped. And when that understanding becomes clear, there would seem to be little problem with it. But we do have to understand to understand. [/QUOTE]

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