Sony fe 600mm f 6 3 gm oss vs sony fe 600mm f 4 gm oss?

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From Sony FE 600mm f/6.3 GM OSS: Sony FE 600mm f/6.3 GM OSS: A prime lens by Sony for Full frame cameras, 600mm f/6.3. A 600mm prime of about a kilogram, for wildlife hand-held. Specs - Maker: Sony - Focal length: 600mm (prime) - Maximum aperture: f/6.3 - Made for: Full frame sensors - Mounts: Sony E - Stabilised: yes - Autofocus: yes What it frames like - On full frame (Sony E): as marked, 600mm. - On APS-C (Sony E): like 900mm ...

From Sony FE 600mm f/4 GM OSS: Sony FE 600mm f/4 GM OSS: A prime lens by Sony for Full frame cameras, 600mm f/4. Specs - Maker: Sony - Focal length: 600mm (prime) - Maximum aperture: f/4 - Made for: Full frame sensors - Mounts: Sony E - Stabilised: yes - Autofocus: yes What it frames like - On full frame (Sony E): as marked, 600mm. - On APS-C (Sony E): like 900mm on full frame; f/4 gives about the depth of field ...

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