Even though we ARE Nikon lovers,we are NOT affiliated with Nikon Corp. in any way.


Sign up Login
Home Forums Articles Galleries News Workshops Shop Recommended
members
All members Wiki Contests Vouchers Apps Newsletter THE NIKONIAN™ Magazines Podcasts Fundraising

A gedanken experiment on light meters....

nl

West Hartford, US
833 posts

Click to send email to this author Click to send private message to this author
nl Basic Member
Fri 27-Mar-09 02:45 AM

Hopefully the topic got your attending. I've been trying to thing something through, and I wonder if anyone can help.

For the purposes of discussion, assume a subject lit by a single light source. Let's also assume the camera has a mathematically ideal zoom lens - eg a lens that can zoom from 0 to infinite focal length, with no impact on image rendering (sharpness, resolution, aberration, etc) at any focal length. In other words, lens characteristics and imperfections have no effect in this thought experiment.

We will make an incident light meter reading by placing the incident meter at subject position, aimed at camera. Obviously, the meter reading is not dependent on the camera position.

Suppose we place the camera at distance "X" from the subject, zoom so the subject entirely fills the frame, and make an exposure. Now we move the camera to position "2X" from the subject, again zoom so the subject entirely fills the frame, and expose.

Since at each camera position we zoomed so the subject filled the entire frame, the light captured at each position can only be light reflected by the subject - in other words, there is no additional light entered the lens from around the subject.

Since we are at 2X the distance on the second exposure, the inverse square law says that the light entering the lens at position 2X is 1/4 that at position X. Therefore, incident metering should be critically dependent on the camera to subject distance, and yet we never seem to take this into account with incident metering.

There seems to be a flaw in my reasoning (and I have a geometrical argument to explain this and correct the reasoning) but I am curious to see what others think first and see if anyone can help me out with my thinking.

Thanks.
nl

Subject
ID
Reply message RE: A gedanken experiment on light meters....
1
Reply message RE: A gedanken experiment on light meters....
2
     Reply message RE: A gedanken experiment on light meters....
4
          Reply message RE: A gedanken experiment on light meters....
5
               Reply message RE: A gedanken experiment on light meters....
10
Reply message RE: A gedanken experiment on light meters....
3
Reply message RE: A gedanken experiment on light meters....
6
Reply message RE: A gedanken experiment on light meters....
8
     Reply message RE: A gedanken experiment on light meters....
11
          Reply message RE: A gedanken experiment on light meters....
12
               Reply message RE: A gedanken experiment on light meters....
13
                    Reply message RE: A gedanken experiment on light meters....
14
                         Reply message RE: A gedanken experiment on light meters....
17
                              Reply message RE: A gedanken experiment on light meters....
18
                                   Reply message RE: A gedanken experiment on light meters....
19
                                        Reply message RE: A gedanken experiment on light meters....
20
                                             Reply message RE: A gedanken experiment on light meters....
24
Reply message RE: A gedanken experiment on light meters....
7
Reply message RE: A gedanken experiment on light meters....
9
Reply message RE: A gedanken experiment on light meters....
15
Reply message RE: A gedanken experiment on light meters....
16
     Reply message RE: A gedanken experiment on light meters....
21
          Reply message RE: A gedanken experiment on light meters....
22
          Reply message RE: A gedanken experiment on light meters....
25
          Reply message RE: A gedanken experiment on light meters....
23
               Reply message RE: A gedanken experiment on light meters....
26
                    Reply message RE: A gedanken experiment on light meters....
27
                    Reply message RE: A gedanken experiment on light meters....
28
                    Reply message RE: A gedanken experiment on light meters....
29
                         Reply message RE: A gedanken experiment on light meters....
30
                              Reply message RE: A gedanken experiment on light meters....
31
                              Reply message RE: A gedanken experiment on light meters....
33
                              Reply message RE: A gedanken experiment on light meters....
32
Reply message RE: A gedanken experiment on light meters....
34
Reply message RE: A gedanken experiment on light meters....
35
     Reply message RE: A gedanken experiment on light meters....
36
     Reply message RE: A gedanken experiment on light meters....
38
     Reply message RE: A gedanken experiment on light meters....
37
          Reply message RE: A gedanken experiment on light meters....
39
               Reply message RE: A gedanken experiment on light meters....
40
               Reply message RE: A gedanken experiment on light meters....
41
               Reply message RE: A gedanken experiment on light meters....
42
                    Reply message RE: A gedanken experiment on light meters....
43
                         Reply message RE: A gedanken experiment on light meters....
44
                              Reply message RE: A gedanken experiment on light meters....
45
                                   Reply message RE: A gedanken experiment on light meters....
46
                                        Reply message RE: A gedanken experiment on light meters....
49
                                             Reply message RE: A gedanken experiment on light meters....
50
                                             Reply message RE: A gedanken experiment on light meters....
51
                                                  Reply message RE: A gedanken experiment on light meters....
52
Reply message RE: A gedanken experiment on light meters....
47
Reply message RE: A gedanken experiment on light meters....
48
     Reply message RE: A gedanken experiment on light meters....
53
Reply message RE: I feel there are four aspects
54
Reply message RE: I feel there are four aspects
55

G