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Photography Q&A
Help me understand FX vs. DX
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<blockquote data-quote="aroy" data-source="post: 519259" data-attributes="member: 16090"><p>There are a few thinks that will clarify the issues</p><p></p><p>. In general DX sensors exhibit more noise that FX sensors of the same generation, so FX bodies will have better (lower noise) high ISO performance.</p><p>. Currently DX sensors have more pixel density compared to the FX sensors. </p><p>. The FOV of a DX sensor is about 1.5 times narrower than that of an FX sensor (24mm width V/S 36mm width). That is same as saying that from FOV point of view the same lens is behaving as a 1.5 time longer lens, which is what has given rise to the "effective Focal Length". For every thing else - DOF perspective etc, the lens is still behaving as its focal states.</p><p></p><p>If an image of an object is 20mm wide in a sensor (here it does not matter what the size of sensor is, the same lens will project image of the same size on either sensor) then for 24MP bodies the sensor has 6000 x 4000 pixels</p><p>- For FX this means 6000/36 = 166.67 pixels per mm</p><p>- For DX this means 6000/24 = 250.00 pixels per mm</p><p></p><p>So a 20mm image will have</p><p>- FX : 20*166.67 = 3333.33 pixels</p><p>- DX : 20 *250.00 = 5000 pixels</p><p></p><p>In effect you have increased the resolution of the image by just using a denser sensor. If you use 36MP sensor then there will be more pixels ~ 4100, but to achieve the same number as DX the sensor needs to be about 56MP.</p><p></p><p>2)</p><p>IQ depends on a number of factors, but sharpness (both center and corner) does increase with the first few stops, but then diffraction effect sets in and images become fuzzier. Most of the Supertelephotos are designed to be used wide open or at the most ones stop down. You may not get better IQ at higher stops, but you will nsurely get better DOF which may matter more in certain cases.</p><p></p><p>3)</p><p>Cropping will not have any bearing on IQ, only on number of pixels. Nor does cropping have any bearing on noise. So in your case if you use an FX sensor, you will get lower noise compared to a DX sensor, but what you gain in noise you will loose in resolution (which normally means a longer lens = more expenses). That is a trade off you have to decide on - shorter lens with more noise or longer lens with lower noise.</p></blockquote><p></p>
[QUOTE="aroy, post: 519259, member: 16090"] There are a few thinks that will clarify the issues . In general DX sensors exhibit more noise that FX sensors of the same generation, so FX bodies will have better (lower noise) high ISO performance. . Currently DX sensors have more pixel density compared to the FX sensors. . The FOV of a DX sensor is about 1.5 times narrower than that of an FX sensor (24mm width V/S 36mm width). That is same as saying that from FOV point of view the same lens is behaving as a 1.5 time longer lens, which is what has given rise to the "effective Focal Length". For every thing else - DOF perspective etc, the lens is still behaving as its focal states. If an image of an object is 20mm wide in a sensor (here it does not matter what the size of sensor is, the same lens will project image of the same size on either sensor) then for 24MP bodies the sensor has 6000 x 4000 pixels - For FX this means 6000/36 = 166.67 pixels per mm - For DX this means 6000/24 = 250.00 pixels per mm So a 20mm image will have - FX : 20*166.67 = 3333.33 pixels - DX : 20 *250.00 = 5000 pixels In effect you have increased the resolution of the image by just using a denser sensor. If you use 36MP sensor then there will be more pixels ~ 4100, but to achieve the same number as DX the sensor needs to be about 56MP. 2) IQ depends on a number of factors, but sharpness (both center and corner) does increase with the first few stops, but then diffraction effect sets in and images become fuzzier. Most of the Supertelephotos are designed to be used wide open or at the most ones stop down. You may not get better IQ at higher stops, but you will nsurely get better DOF which may matter more in certain cases. 3) Cropping will not have any bearing on IQ, only on number of pixels. Nor does cropping have any bearing on noise. So in your case if you use an FX sensor, you will get lower noise compared to a DX sensor, but what you gain in noise you will loose in resolution (which normally means a longer lens = more expenses). That is a trade off you have to decide on - shorter lens with more noise or longer lens with lower noise. [/QUOTE]
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