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03-15-2007, 06:06 PM   #16
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Join Date: Feb 2007
Location: Maryland
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Link & Lock Test

RiceHigh asked "if the camera is set to "linked AF to AE" but the user has set the multi-AF point manually, I don't know if the manually selected (single) AF point is counted or the AF measurement works as it was in "auto 11 points".

I just finished testing this. Setup was sitting at a table with a light colored marble top with a light hanging over it in an otherwise dark room. I composed my picture so the frame was half on the table and half on the dark room areas (it's night here) beneath and beyond the table top. This made half the frame very bright and half very dark. There was at over 2 stops difference in exposure.

BOTTOM LINE UP FRONT: the K100D performs as the manual says it should in all metering modes. Here are the details for all you (other) obsessive compulsive types:

1- TEST 1=AE and AF Linked:
a-Spot metering: If I moved center AF point just off edge of table (on dark area), locked focus and took picture, the dark area was properly exposed and table top was overexposed. When I moved center AF pt to be just onto the table top, table was properlly exposed and background was under exposed. Both these situations are as you'd expect. If I repeated the test, but repositioned the center AF (and linked AE) point to the opposite lighting area after locking focus, the resulting exposure was correct for the final area, not the area in which AF was locked. Again, this is as it should be if AE and AF are linked, but not locked. Focus remains locked on target, but as center metering point moves over differently lit area, exposure adjusts.
b-Select metering: I repeated the above test, but instead of having to move the composition, I left the central AF point on the divide between low and high expsoure areas. I moved the AF point with the 4 way controller. Again, when AF point was on table top, table was exposed properly; when I moved it to dark area, that was exposed properly. If I locked focus on dark area, then moved frame to be totally filled with bright table top, table top was properly exposed. If I started with AF point locked on table top, then moved entire frame to dark area, dark area was properly exposed. This again shows that AE and AF are linked, but not locked, and that if you reposition after locking focus, exposure will change.
c-AUTO metering: This was a little trickier as I had to play around a bit to get the AUTO system to focus on the dark area. But in the end the results were the same as for 1a, b above. After you lock focus, AE changes to properly expose wherever the AF (and linked AE) point is when you take the picture.

2- TEST 2=AE-AF linked AND AE-AF locked (same lighting conditions as above):
a-Spot, Select and AUTO metering modes: This time the exposure taken was correct based on where the AF point was when the AF was locked. Thus, unlike the first test, if I locked AF on a dark area, then moved the composition to be fully filled with the birght table top, the picture was way overexposed. If I reversed the process locking on light surface then moving to dark area, the picutre was underexposed. I also did some halfway tests that showed theat the resulting exposure setting was correct for the area in which the AF was locked.

The lesson is perhaps obvious, but if you tend to lock your focus point then recompose, you need to be aware what that may mean for your exposure. Unless you spot meter, the effects might not be too severe in a general lighting situation. However, when the lighting levels are large, you will probably want to use the AE-AF link and/or lock features (or AE-L lock button if you like to recompose after locking focus) in trickier situations (e.g., person in foreground with brighter scenery behind).

This may have been a "blinding flash of the obvious" to you more experienced folks, but I hope it was useful to those of us less experienced with the outstanding metering system and all teh "bells and whistles" of the K100D.

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