也論50mm

1. We are talking about 50mm lens for 35mm SLR cameras.

2. The technical spec defines the distance from the lens mount to the film/sensor to be about 40mm, leaving enough clearance for the reflex mirror.

3. As a result, the distance from the lens to the sensor/film is about 50mm. Which means 50mm will be the easiest lens to make (smallest size).

If the lens has a longer focal length, it of course must be bigger/longer.

But if the lens has a shorter focal length, it will be shorter than the distance from the lens mount to the sensor, thus the designers of the lens have to do some tricks to place the lens farther away than its focal length, resulting in a bigger lens.

4. Conclusion: 50mm lens is the cheapest to make, thus included as the "standard" lens in the old days.

5. So using 50mm lens is because:

A. Cheaper
B. Small size, so that it is most convenient to carry around.
C. Not because it is special in other aspects (say, providing the best field of view in photography).

6. For mirrorless camera, the lens mount can be placed closer to the sensor/film, thus resulting in a shorter focal length lens as the most natural lens.

7. The above is from my own analyses. If some one already came up with the same analyses, it is totally coincidental.

所有跟帖： 

• a very good analysis~~ -不加分析- ♂ (0 bytes) () 03/05/2012 postreply 12:20:10

• Thanks! -pieq314- ♀ (0 bytes) () 03/05/2012 postreply 12:27:31

• 多謝，學習了知識 -車頭- ♂ (0 bytes) () 03/05/2012 postreply 12:24:43

• 嗬嗬，太客氣了。 -pieq314- ♀ (0 bytes) () 03/05/2012 postreply 12:27:49

• hi, 問個好，久不見了。 -偶爾貼貼- ♂ (0 bytes) () 03/05/2012 postreply 12:30:43

• 是啊，久不見了。 -pieq314- ♀ (21 bytes) () 03/05/2012 postreply 13:00:16

• 我也有你這想法，但沒你這麽詳細的數據 -akuan- ♂ (0 bytes) () 03/05/2012 postreply 12:31:09

• 嗯，好！謝謝 -pieq314- ♀ (0 bytes) () 03/05/2012 postreply 13:01:17

• 學習了。 非常感謝。 -天天古狗- ♂ (0 bytes) () 03/05/2012 postreply 12:34:41

• 不用謝，嗬嗬 -pieq314- ♀ (0 bytes) () 03/05/2012 postreply 13:01:34

• 不同意。flange是固定的。鏡頭，焦距越長鏡頭越長，光圈越大鏡頭越粗。反之亦然 -WayCool- ♂ (33 bytes) () 03/05/2012 postreply 13:09:11

• 手裏正把玩UPS剛送到的20mm/f2.8。跟我的5014一樣長，不過更粗重。 -U96- ♂ (56 bytes) () 03/05/2012 postreply 13:12:49

• Let's compare 35mm f/1.4 (I do not think Canon has 28 f/1.4) and -pieq314- ♀ (75 bytes) () 03/05/2012 postreply 13:18:31

• 派兄說的是事實。 -吉火- ♂ (127 bytes) () 03/05/2012 postreply 13:22:50

• 怎麽說吧。小於50mm的鏡頭長度不是個因素，你的理論還是不能成立 -WayCool- ♂ (0 bytes) () 03/05/2012 postreply 13:51:43

• 對我來說定焦鏡頭還有一個非常重要的特性就是大光圈。 -schatten- ♂ (0 bytes) () 03/05/2012 postreply 13:14:55

• That is the only reason for me: larger aperture. -pieq314- ♀ (131 bytes) () 03/05/2012 postreply 13:21:15

• 用片支持一下 （一張） -偶爾貼貼- ♂ (217 bytes) () 03/05/2012 postreply 13:46:14

• 片沒出來，不會整了。有主意嗎？ -偶爾貼貼- ♂ (0 bytes) () 03/05/2012 postreply 13:55:51

• Maybe pbase does not allow external link? -pieq314- ♀ (0 bytes) () 03/05/2012 postreply 18:48:38

• 我在大大仙那樓裏就說過，用50mm就因為它最便宜。哈哈 -用戶名被占用了- ♂ (0 bytes) () 03/05/2012 postreply 18:38:41

• 就是嗎。 -pieq314- ♀ (0 bytes) () 03/05/2012 postreply 18:54:01