想买个人像头，在纠结哪个焦段(有妹子)

最近想入坑人像了，然后就约了一个妹子出来当模特，用的是尼康的小驴炮，在光线不好下用着有点不好用，想买个大光圈定焦玩玩，然后又在纠结焦段了，有没有推荐的水友，机身是尼康z6(转接和原厂都可以，价格的话6000一下吧)
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