True magnification with zoom lenses

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ingweDave

ingweDave

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I was watching one of the video reviews of the Nikon 180-600 being compared to the Sony 200-600. It was shown that the Nikon lens was closer to representing the true magnifications as the camera was moved closer to the subject. With the Nikon showing a significantly larger image, at the same focal distance, compared to the Sony.
Can one of you clever people out there, explain this in simple terms? Is it only a factor with zoom lenses?
 
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ingweDave said:
I was watching one of the video reviews of the Nikon 180-600 being compared to the Sony 200-600. It was shown that the Nikon lens was closer to representing the true magnifications as the camera was moved closer to the subject. With the Nikon showing a significantly larger image, at the same focal distance, compared to the Sony.
Can one of you clever people out there, explain this in simple terms? Is it only a factor with zoom lenses?
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The max focal length is typically calculated with the focus set at infinity, and as you pull in focus, you're seeing a "zooming effect" and your field of view and magnification change. So if the bird is at 20ft away, your focal length might actually be 560mm. Zooms are harder to correct but this is actually a problem on primes too. Sony lenses (mk I and non-GM) have more of it than Nikon and Canon, and they recently introduced an in-camera focus breathing compensation feature. It works, but it crops in so many dislike it.

Big issue for video.
 
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