上次我发现， 用我的S50拍摄的不少超近距离的东西（花），
很多都有焦距不准的问题。 (distance 10-30 cm)

问题： digital camera 的对焦， 是从哪里开始计算的？
1） 从镜头最前端？(以下简称 "镜头端")
2） 从像机靠后的地方(好的film camera那个地方会有一个记号)?(以下简称 "像机后端")

我用我的S50做了一下初步实验:

下图是布置: 用一张标准的 letter paper, which is 216 mm width.
Bend it into 4, place a coin in each line, each coin to coin should
be 54 mm (5cm roughly). Camera is placed in the front side of
the paper (so it is about 5cm to the first coin, 10 cm to the second coin,
15cm to the thrid, 20cm to the forth). ,




The following figure is taken when:
align the front paper line to the camera's 像机后端
set the camera to use manual focus, set focus distance to 10 cm.
We can see that the first coin (5cm away) only show a corner.
And in the 4 coins, no one is in focus.



The following figure is taken when:
align the front paper line to the camera's 镜头端
set the camera to use manual focus, set focus distance to 10 cm.

The following figure is taken when:
align the front paper line to the camera's 像机后端
set the camera to use manual focus, set focus distance to 20 cm.



The following figure is taken when:
align the front paper line to the camera's 镜头端
set the camera to use manual focus, set focus distance to 20 cm.

PS:
Click each figure to open its bigger version figure for details.
The bbs shrink them so that can not see clearly.

So, in the 10cm example, it seems that the focus length should start
at the lens's position (镜头端).

In the 20cm example, it seems not differ too much. (从"镜头端"到"像机后端"大概
4cm).

any idea?

I will try to come up with a more detailed example with better light later.

(更正： 图片刚才贴在后面了)

今天又做了一些实验, 步骤就懒的贴了. 我的结论是:

条件:
不用zoom的时候,
用f 2.8
不用macro mode.
用manual focus.

when manual focus set to 10cm:
most clear position: around 9cm from the lens
10 cm from lens is acceptable.

when manual focus set to 20cm:
most clear position: around 17.5 cm from the lens
19 cm from lens is acceptable.

This is only for my camera.
I belive different cameras may vary a little.

:-)

[此贴子已经被作者于3/23/2004 2:55:09 AM编辑过]

以下是引用dollhouse在3/22/2004 10:14:04 PM的发言：
这个gg好好玩哈^^
搞科研第吧^^

和和， 各行各业都要有研究精神。 :-)

这个是设置像机为 10cm focus 是的结果:
手写的数字是到镜头的距离(cm)。

这个是设置像机为 20cm focus 是的结果:
手写的数字是到镜头的距离(cm)。