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11-08-2013, 05:04 PM   #1
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FA/DA comparison

I am using A K-x with a 55-300 DA-L telephoto. I have just purchased a used FA 100-300, believing that it would perform like a 450 because it is a full frame lens, but it does not. What am I missing here?

11-08-2013, 05:08 PM   #2
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QuoteOriginally posted by SWilde Quote
I am using A K-x with a 55-300 DA-L telephoto. I have just purchased a used FA 100-300, believing that it would perform like a 450 because it is a full frame lens, but it does not. What am I missing here?
300mm is 300mm. Just because the FA lens covers a wider image circle doesn't mean it's any longer

450mm on film would give you the same field of view as 300mm on digital. But that doesn't make a 300mm film lens become any longer when mounted on a digital camera.

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11-08-2013, 05:28 PM   #3
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Focal length is not the same as field of view. A lens has its focal length written on it, and whether its made for FA or DA makes no difference. It would make a difference if you used a DA lens on full frame, because the edges would be dark (due to smaller image circle).
Your DA is already "performing like a 450"
11-08-2013, 05:36 PM   #4
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Don't feel bad, common misperception.

11-08-2013, 06:00 PM   #5
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As mentioned above, 300mm is 300mm whether on 24x36 or a cropped APS-C camera. The reason people say it's comparable to a 450mm is due to the sensor size, not the lens. Here's an image to help explain.

A full frame sensor, or 24x36 film camera, would capture everything in the red square with a 300mm lens. Your digital just captures the yellow box.

Don't pay attention to equivalent focal lengths, 450mm on a film camera would essentially capture the same yellow square as a 300mm would on your digital camera, but the focal lengths are not the same so the subject would not be proportionally the same size. Cropped format is a fitting name, because that's exactly what your sensor is doing: cropping the image. That's why 300mm is 300mm on either format. I hope this helps.
11-08-2013, 07:46 PM   #6
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Another way to explain:

Your DA 55-300 and the FA 100-300 have exactly the same max focal length (300mm), you're just using the center of the FA 100-300 because it's a full-frame lens with a bigger image circle (that goes wasted because it doesn't hit the sensor on the APS-C digital). In effect, it doesn't give any extra "reach", the size of the image formed on the sensor is the same on both lenses.

It's not a complete waste though. Because you're using only the center of the FA lens, it's potentially sharper, even though the DA version has an ED element.
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