CanadaMark
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bs kite wrote:
Thanks for your interesting comment. I would not have known. And I feel you are unbiased.
You can actually look this up if you're interested - it's part of the lens specification that most manufacturers publish. Look for something like "maximum reproduction ratio" in the list of lens specifications. It doesn't tell the whole story, but the higher the number, the greater the magnification. The Nikon 180-600 is 0.25X, the Sony 200-600 is 0.2X, so the same image taken with the Nikon lens will appear 25% larger when each lens is set up to produce it's highest possible magnification.
I don't think anyone has published a chart yet that shows the "effective" focal length at any given subject distance, but arbitrage is correct that the Sony 200-600 changes it's magnification quite significantly as you get closer to MFD. A 600mm lens is only guaranteed to be ~600mm at infinity, but the Nikon 180-600 seems to stay very close to 600mm at all focus distances. Prime lenses generally have very little change but zoom lenses are usually the worst offenders. Nikon's F mount 70-200 VR II was notoriously bad for this, as it had a magnification change resulting in a loss of about 30% of it's effective focal length at MFD. The Sony drops down to around 530mm at close distances which is quite noticeable in use.
Focus breathing is not the correct term for what is being described here but I don't think that's worth getting into as everyone still knows what the point is.
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