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Exposure to the right (ETTR) is a technique of setting the exposure of a scene such that few or no pixels are are over exposed (blown out) thus maximizing the information captured without loosing information to over-exposure. This may produce a darker image but this can be corrected later in post processing. The exposure curve is thus as far to the right as possible without it being clipped.
There are two methods (three really) of using ETTR:
The first method involves taking 2 images. A shot is taken then ETTR looks at it and it modifies the exposure for the next shot. There are two ways to use this method: Always on and Auto snap. The Always on setting sets the ETTR for the next shot on every shot you take for the next shot. The Auto snap setting takes a shot, calculates the ETTR, and then takes the second shot immediately.
The second method uses the live view momentarily to run through a series of exposures until the exposure is correct without taking a photo. You then take the photo.
ETTR sets the shutter speed and ISO. It does not change the aperture setting thus not altering the depth of field of the scene.
In the Expo Tab (Exposure Menu of ML) you will find Auto ETTR:
Pressing the Q button brings you to the settings menu of the ETTR function:
Trigger mode: Always ON, Auto Snap, Press SET, HalfS DblClick. The mode that AutoETTR uses to perform it's function.
* Always on means that every time you take a picture the image is displayed in the LCD monitor with an analysis of the image and the shutter speed and ISO are set for the next shot.
* Auto Snap means that every time you take a picture the image is displayed in the LCD monitor with an analysis of the image, and that if the results are not adequate it will automatically take another image.
* Press SET means that every time press the SET button the current scene is displayed in live view, the image is analyzed by stepping through a series of exposure settings. When finished, live view is turned off and the shutter speed and ISO are set, ready for the shot.
* HalfS DblClick does the same thing as Press Set but with a quick double tap of half shutter.
For Timelapse set it to Always on.
Slowest shutter: 1/60 The slowest shutter that will allow for the current scene. . For a night time lapse set it to 30 seconds.
Highlight Ignore: 0.2% Percentage of (highlight) pixels to ignore when calculating ETTR. This is used if you want to allow overexposure in the highlights, for example room lights. Typical setting is 0.2% and means ignore almost nothing. If you want to ignore more highlights try 1, 3, 5 or even 10%. If the timelapse has the sun or moon in it, you may want to raise h.i. to 5% or more. Otherwise the scene will be too dark.
Midtone SNR limit: 6 Is defined in EV levels of noise in the Midtones form 1 to 8 EV. The higher the SNR the less noise. Typical settings from 4 to 8 EV. For a Timelapse we recommend 4, 5 or 6.
Shadow SNR limit: 2 Is defined in EV levels of noise form 1 to 4 EV. The higher the SNR the less noise. Typical settings from 2 to 4 EV. For a Timelapse we recommend 2 or 3.
If you want more visual feedback as to what's going on, enable histograms and raw zebras:
In the Overlay Tab you can scroll down to Histogram and press Q to configure:
RAW EV indicator: OFF Here you can press the set button and select ETTR hint. This will display in the RAW histogram a hint of how many more EVs you can expose to meet the ETTR parameters set in previous menu.
Also in the Overlay Tab you can scroll to Zebras, press Q, and make sure that RAW zebras are ON. The RAW zebras will show on the image itself to mark the areas where a color channel may be overblown.
ETTR in RAW images - HOW TO USE IT (step-by-step):
If you do not have ML installed in your camera go here: RAW video & ML – Beginners Guide and FAQ – READ FIRST http://www.magiclantern.fm/forum/index.php?topic=5520.0
1. Go to Canon Menu a set Image Review: hold (This gives you a change to review the RAW histogram until you press half shutter to stop the preview, 2 sec is too quick to analyze the histogram but you can set it as desired NO LESS THAN 2 SEC!
2. Put the camera in manual M mode or Av mode (it makes no difference since you must the aperture yourself), and set ISO to any number except in Auto. It wont work in auto!
3. Press trash button to enter ML menu.
4. Go to the Expo Tab and enable Auto ETTR by pressing set.
5. Press Q if you want to change ETTR details. Default settings are good but you may want to adjust Slowest shutter depending on your needs.
6. (optional) enable Global Draw
6.1 Press Q and move to Overlay Tab. Make sure Global Draw in: On, all modes.
7. (optional) enable Zebras
7.1 Scroll to Zebras, press Q, scroll to the bottom and select Use RAW zebras ON.
7.2 Press Q
8. (optional) enable the Histogram
8.1 Scroll to Histogram and press Q
8.2. (optional) Scroll to RAW EV indicator and select ETTR hint by pressing set.
8.3. Press Q
12. Press trash button to exit ML menu.
13. Frame you subject and set the aperture and shoot a test photo.
14. Now look at the display and you should see the image. If the current M settings are not optimal the camera will calculate new settings to be used in the next photo.
The new important features that you are looking in the display are:
RAW histogram on the bottom right is a small graph.
a. Inside this histogram you may see near the top-left of the graph, in white lettering, the letter E followed by a number which represents how far you can go, in EV numbers, to reach ETTR, i.e E1.2 b. Inside the RAW histogram near the bottom you may see colored circles with numbers inside which represent the overblown channels (R, G, B) and the number of EV of over-exposure. To see this aim to an area with higher more light and take a pic. c. If there are overexposed areas you will see RAW Zebras in the color which is overblown.
13. Take another picture without changing the scene and you will see how the camera settings are adjusted to meet the ETTR requirements. If the camera beeps it means that the photo is out of specs and you should shoot again. In the tests I ran I found that in extreme situations the adjustment was completed in three photos. For most situations the adjustment is done in one shot.