Auto Exposure Bracketing

[Relysis38]

Why and when would AEB be used? I have a Canon EOS 400D and have noticed that in the manual there is a section on Auto Exposure Bracketing. I have read the instructions and even used the utility, step by step, but couldn't understand why or when it would be used.

[Palladius]

Some scenes can be tricky to expose correctly... they might contain a wide range of light levels, or lots of very bright or dark areas that will throw off your camera's meter, or you may just not be very sure what exposure will lead to the best shot.

One of the ways round this is exposure bracketing... you take one shot at the exposure you think is about right, say 250@ f/5.6. Then, to make sure, you take one over-exposed and one under-exposed say f4 and f8. That way, even if you were a bit off originally you'll hopefully have something good. It's not quite so important now we have LCD screens and histograms, but it was a life-saver when you had to have film processed.

Of course, you can just shoot RAW and then fudge it afterwards, but it's better to get it right in-camera.

[Swisstony10]

When I shoot landscapes and sunsets, I regularly use bracketing - and then use the three resulting images to chuck into Photomatix to give me either a more balanced or an HDR type image. The same applies for buildings if you have an area of sky above it and you want a nicely-exposed building with a dramatic sky.

Also, as Palladius suggested, it's really useful if you're not entirely certain about the exposure - I was out the night before last taking photos of some live bands, and I used the AEB a fair bit, because the bands were moving around a lot, and the lighting was REALLY difficult. I reckon using AEB probably gave me a good 20% more keepers than I would've had.

Russ.

[kencaleno]

Here's the secret to getting a perfectly exposed shot everytime- (as long as your subject area is within the 5-stop dynamic range of the camera's metering system)

1. Know how your camera handles exposure-( I know that mine overexposes between 1/3 and 2/3 of a stop-depending on lighting conditions)

First, calibrate your camera's meter:

a) Set camera mode to “P”/P-shift“, or “A/AV” Use Matrix/evaluative metering-(Scene should contain all tones within dynamic range)
b) Hold +/- button, (On Nikon’s, Near shutter button: Canon‘s is to the right of LCD screen) and turn command dial to + 1.0 - take a shot

Next ……………………………….................turn command dial to + 0.7 - take a shot
Next………………………………..................turn command dial to + 0.3 - take a shot
Next………………………………..................turn command dial to - 0.0 - take a shot
Next………………………………..................turn command dial to - 0.3 - take a shot
Next………………………………..................turn command dial to - 0.7 - take a shot
Next………………………………..................turn command dial to - 1.0 - take a shot



You will have 7 shots from + 1.0 to - 1.0 study these for one with detail in shadow and highlight areas, without blown highlights (Switch on the “blinkies” to show blown highlights)
Set exposure compensation (+/-) to this best shot reading, and keep it there for all outdoor shots
Once set up, this will be pretty accurate.

Set metering to "spot metering" mode
Set auto bracketing to 2/3 EV (With camera calibrated as above you should not be more than 1/3 EV(0.3) out at any one time)

Use A/Av mode to select depth of field

set white balance to appropriate Kelvins as below:

Where, with film you either shot print film in daylight or with flash indoors, and with slide film, you used daylight or tungsten film, or used compensating filters with these. White balance is Digital’s version-you select a white balance based on the condition of the light you are using, so the camera’s meter allows for white to photograph as white
Auto white balance does a reasonable job most of the time, but it cannot cope in some situations-especially when subject is in deep shadow. You need to know when to use the white balance settings for all situations, and this table will help you understand: ( degrees Kelvin is a means of determining colour temperature)

Sunrise/sunset 2400-3000 Kelvin……………………Use Auto white balance
Tungsten lighting 3200-3500 Kelvin ……………………Use tungsten/Incandescent white balance
Fluorescent lighting 4000 Kelvin …………… Use fluorescent White balance
Early morning/afternoon sun 4000 Kelvin…….Use auto white balance/ --fluorescent white balance
(Magenta filter) to counter greenish cast on skin from foliage if under trees or on really green grass
Noon sun/Sun overhead…5000-6500 Kelvin…………………….use Cloudy White balance
Flash photography in daylight 5500 Kelvin ………………………Use Flash White balance
Deep shade………………….6500 Kelvin…………………………Use cloudy/shade white balance
Shade in daylight 7500 Kelvin ………………………………......Use shade white balance
Heavy overcast, very dark shade 8000 to 10000 Kelvin………Use shade white balance plus 81a-85c glass filter

To set custom White balance: (Nikon)

Select a neutral coloured object to set your white balance
It’s best to avoid using a white target. The camera prefers grey..( Print yourself a grey card: In photoshop- File> New
Click on background square in toolbox
select 127;127;127 from color chart-Print)
If you use white in direct sunlight you'll always get a "No Gd" response from the camera because the Matrix meter is rendering it white instead of grey. Thus the trick is to select the centre-weighted meter when using a white reference in bright light and you'll get "Good" from a camera. Remember to set back to Matrix metering as soon as you're done.

Ok, so you are going to have problems if some images you want to make, are outside the dynamic range of the camera: So here's the plan for that:
With camera on tripod: meter for highlight, take a shot-then meter for shadows, take another shot. In Photoshop:
1. Add lighter image to darker as a new layer,( click on Move tool,hold down "shift" button,and drag lighter image over to darker,then release) then:
2. Select> Color Range-Click highlights
3. Check “invert”, click “OK”.
4. Add layer mask. Click on layer mask
5.Filter> Blur> Gaussian Blur 250 pixels.Click "OK"
Flatten and save. You will get detail in highlights and shadows. (See thumbnails below)

image#1 exposed for sky;
- #2 exposed for foreground;
#3 Blended in photoshop

Now you know how to get perfect exposure-



Regards, Ken

[Swisstony10]

*grins* As always, Ken is The Man...

Ken - have you ever thought of publishing a how-to book? It'd be so nice to finally get one which is totally comprehensive while still being intuitive and easy to follow..

Russ.

Good info Ken as always

[Relysis38]

Thank you gentlemen. The information you all provided is very clear. I can now understand why and when I would use AEB. I agree with Swisstony10, the book would be the thing. Thank you all once again for your help.

Ted