Saturday, September 12, 2009

What Exposure bias to use

Goal: To determine what exposure bias (EB) to use for shooting humans under the bright sun of the day

- Imitation of this problem => Goal: expose the books well (imaging them as human faces), and the light as the sun in the high sky.

Note: all pics today are with Tungsten White balance setting, manual mode and spot-metering.

Normal procedure we usually do:

- no flash
- spot-metering off the beige cover of the light stand.
- +1EB as it is white and should be white (so I expose more => +1)
- But the books are almost invisible (like dark human face under the sun)

- no flash, but now spot-metered off the books so that the books will have the +1EB exposure that I'll set

- the books are much better exposed then last pic, but they are still too dark

- diffused flashed added as fill-in flash to light the books (as suggested on many websites for fill-in flash)

- spot-metered off the books and set +1EB
- then recompose the frame, and shoot

- now the books are nicely exposed, but the background is too bright.

- Same dilemma as shooting people under high sun of the day.
-still don;'t know how to fix this.
- This book and light problem is worse because books and light are too close.

Take Away
- use spot-meter on the object that you want to have the correct exposure. That spot-metered object will be the only thing in the frame that will have the exposure you will pay attention to. The rest will be too bright or too dark or wrong, but that tiny point in the frame will have the setting you set to.
- recompose if necessary, but recomposing alters the just-set exposure from spot-metering, but shouldn't be too bad.

Test 2 of the Day

Goal: to determine what exposure bias (EB) to use

- EB = 0
- spot-metered of the black hair. Thinking that's the point among the whole frame where I want to have correct exposure reading.
- I was wrong
- it was too bright, hence the hair was not dark enough

- spot-metered off the black hair
- I want the black hair to be black in the pic, and from last pic it's too bright, so now I lowered EB=-1 to get the black darker
- black hair seems right now

Take Away
- If you want to expose dark things as dark, set EB to negative
- If you want to expose white things as white , set EB to positive
- Never spot-meter too white or too black objects as neutral EB=0. That is just wrong.

Test3 of the day

Goal: What EB to use for shooting bright light sources
Imagine: taking the bright sun on the sky with lots of clouds. To get the sun as an eclipse-looking ball, use the first pic "normal" techinque => under-expose

- 0EB
- too dark

- +1EB (since last pic was too under-exposed)
- still too dark

-spot-metered off the light ball
- +infinity EB (blinking needle on the far positive end)
- half-pressed the button to make the camera focus on the light ball, then drag /reframe it to sent to 1/3 then pressed the rest of the button
- maybe I should have had the light on the lower right corner

Take away
- To shoot the bright lights, always always over expose them (until after the meter needle was blinking off the chart on the positive side) . Because the light sources are very bright and you want them to be very bright. So need to over expose them very well.

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