I personally wouldn't want to trade in my FX for DX even when solely birding. I was tempted for a bit by the D7200 since it was there in the shop window smiling at me.
The reality is that where I live, an FX allows me to shoot throughout the year while a DX is limited during at least four, five months of that year. For me it is more reach vs more shooting. During good light it doesn't matter but when light gets low, the FX always has at least a two stop advantage on the DX which translates in being able to shoot earlier, later, faster or more closed down depending the type of shooting done.
Of course there's no law that says you can't have both.
The reality is that where I live, an FX allows me to shoot throughout the year while a DX is limited during at least four, five months of that year. For me it is more reach vs more shooting. During good light it doesn't matter but when light gets low, the FX always has at least a two stop advantage on the DX which translates in being able to shoot earlier, later, faster or more closed down depending the type of shooting done.
Of course there's no law that says you can't have both.
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