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Old Jun 14, 2005, 3:23 PM   #1
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Does anyone know how to figure out what the actual zoom of a len on DSLR's? I have seen where you can take a 70-200mm lens and the actual zoom is longer then 200mm. Am I correct on this assumption?

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Old Jun 14, 2005, 5:45 PM   #2
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Because the sensor inside most DSLRs is smaller than 35mm film, the resulting image presented upon it looks as if more zoom was used than was actually the case. While not technically accurate, the result looks very similar. The difference is commonly referred to as a 'crop factor' or 'conversion factor'. For Canon 20D, 300D and 350D this 'factor' is 1.6. So the effective focal range of a lense on one of these cameras is equivelant to that lense multiplied by 1.6. So a 100mm lense will act like a 160mm lense. On the Nikon D70 I believe the factor is 1.5. The exact factor used will be different by brand and sometimes by model - for instance I believe the professional level Canon's may have a 1.3 conversion factor. Does this help?
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Old Jun 14, 2005, 8:37 PM   #3
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John is quite right. Different digital slr cameras have different magnification ratios. Nikon has 1.5 magnification factor. Canon varies from full frame for their Mark II and 1.3 for their Mark I to 1.6 for the rest of the line up, including the rebels.

The magnification factor has always been a blessing for telephoto enthusiasts, more bang for your buck. Your 200 now becomes a 300 or 320 at the same aperture. However, wide angles take a hit, which is why so many new digital only lenses (dx for nikon, -s for canon) are around.

Let us know what your digital camera is and we can give you more info.



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Old Jun 14, 2005, 10:29 PM   #4
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So I am looking at a D70. The Conversion factor for that is 1.5, right? So that would make it 1.5:1 right?
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Old Jun 15, 2005, 12:38 AM   #5
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