Unverified88% confidenceDecision RuleTime unknown
恒定光圈（如f/2.8、f/4）全焦段进光量不变，测光曝光稳定；浮动光圈（如f/5-6.3）在长焦端光圈缩小，弱光和飞行拍摄时快门速度会掉，打鸟建议至少长焦端f/6.3且机身高感表现好
1
Sources
88%
Confidence
Long-term
Relevance
-
First Seen
Sources
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Unverifiedf/2.8恒定光圈变焦的虚化和进光量约等于f/4定焦，若追求人像浅景深奶油虚化，应直接上85mm f/1.8定焦而非依赖变焦头的2.8光圈81% similarUnverified变焦卡片机的长焦端光圈通常收缩至F2.8-F4.5，虚化和进光量远不如广角端的F1.8；若主要拍人像虚化，选固定大光圈定焦（F1.7-F2.8）比选变焦更实际80% similarUnverified70-200mm f/2.8恒定光圈是室内运动、婚礼、舞台的标准配置，全程f/2.8保证暗光快门速度；若只拍白天户外，f/4版本可减重约300-500g且画质相近80% similarUnverified镜头等效24-100mm覆盖广角到中长焦，F1.8大光圈仅在广角端，焦距拉到长焦端后光圈收至F2.8，弱光下使用长焦端画质会明显下降。79% similarUnverified自动对焦系统对最小可用光圈有要求：老款机身多要求f/5.6以上才能相位对焦，若加增距镜后光圈小于f/5.6可能无法自动对焦或仅能中央点对焦；新款机身（如支持f/8、f/11对焦）则限制更宽松78% similar
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