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Frequently Asked Questions and Answers
Exposure
Mar 20, 2021 12:46:03   #
Rongnongno Loc: FL
 
Aperture
 → Depth of Field
 → Depth of Focus
 → F-Stop
 → T-Stop
Bracketing
► Diffraction
► EBTR
ETTR
ETTR rmalarz
Exposure triangle
► ISO
► Over Expose
► Speed
► Under expose

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Mar 20, 2021 13:37:07   #
Rongnongno Loc: FL
 
Aperture

Aperture controls the flow of light that reaches the sensor. (Compare it to a faucet flow)
The aperture is controlled by a graded aperture ring or the camera. The unit is F-stop.

A lens aperture controls the Depth of Field* (DoF) in front and behind the focus plane.
At its widest setting the DoF is narrow. (Wide open, low number in the aperture scale)
At its smallest setting the DoF is deeper. (High numbers in the aperture scale)

Working in conjunction with ISO and Speed this is how you control a scene's exposure as viewed with a camera.

Aperture can be controlled using the camera options:
► Aperture priority
► Manual
Controlling the DoF over an area of interest is the priority when using A Mode (Nikon).

Aperture priority allows to:
► Subject's separation from the background
► Augment/control the acceptable field of focus for landscape photography

A correct setting of the aperture is absolutely a necessity as the aperture setting can and will affect the image quality. This setting depends on the type of lens used as well as the optimal aperture for that lens. Hint: It is rarely at the widest setting. Test your lens.
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* Depth of field is also referred to as the acceptable field of sharpness.

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Mar 21, 2021 01:32:22   #
Rongnongno Loc: FL
 
Bracketing

Bracketing is simply taking different captures at different exposures of the same scene in order to create a wider dynamic range blended image. Please note that bracketing works best with a static scene. Anything that is moving can create ghost artifacts. A tripod is recommended.

Conventional bracketing uses F-Stops.
 ► One capture is normally exposed the other captures are equally under/over exposed
  → -xx -x 0 +x +xx (5 exposures x = F-stop value)
 ► The images are blended together in Post-Processing.

With today's camera and using the raw file format bracketing may seem to be a thing of the past. It would be an error to dismiss bracketing out of hand. To obtain good if not greater results with today's camera, forget the F-stops. Simply take three shots, preferably with a tripod. One for the highlights, one for the mid-tones and one for the shadows.

The real question is what to bracket. It is a thorny issue as Aperture, Speed and ISO create their own issues.

Bracketing with:
 ► Aperture changes the acceptable field of sharpness and will create unwanted softness.
 ► Speed is the best solution*. Moving objects can appear as 'ghosts'.
 ► ISO can create color noise simply because the middle exposure will already be at a higher ISO in order to have 'space' to under expose the scene.

Bracketing is basically stacking for exposure.

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* Opinion and experience.

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Mar 21, 2021 11:08:37   #
Rongnongno Loc: FL
 
Exposure triangle

The exposure triangle is named as such simply because you have three variables to play with:
 ► Aperture, Controls the light (think of as opening a faucet to control the flow of water)
 ► Speed, Controls the length of time (think of time used to fill a bucket)
 ► ISO, Controls the sensor ability to record a scene (think of a bucket)

Each setting affects a different aspect of a capture
 ► Aperture controls the brightness and the DoF (Field of sharpness)
 ► Speed controls the shutter. It affects blur in a picture.
 ► ISO controls the camera sensor array's sensitivity. The setting primarily affects noise.

There is no set formula as to what is right other than reaching a balance.
 ► You need a long field of sharpness? Use Aperture as 'master'.
 ► You need to freeze an image or to create a blur effect? Use Speed as 'master'.
 ► You need... Actually don't unless you really have to. ISO influences noise...

The name is really misleading as many think of a closed triangle as changing one setting means changing the parameter of the other two in order to create a 'balance'. In reality there is no balance.

When it comes right down to it, 'Proper exposure' is not 'proper' at all. It all depends on what you want to achieve. Do not let numbers stunt your creativity. Under or over exposed images can be just as relevant as a 'proper' exposure. Beside if you use bracketing, you skew the numbers to create under/over exposed exposures in order to blend together...

Books have been written on the exposure triangle. They all forget the main ingredient... LIGHT.
Essentially light quality is your guide to an exposure that answers your needs and wants, nothing is more important.

In conclusion...
Learn the effect of each setting, the relationship between them and 'throw the book away'.

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Mar 27, 2021 19:06:47   #
Rongnongno Loc: FL
 
Depth of field
Also named Acceptable Field of Sharpness yet while closely related they are not quite the same.

The Depth of Field depends on the main things, in order of importance:

Lens used
Distance camera/subject
Aperture

The shorter the lens length the longer the DoF. The longer, the shorter up to create a 2D separation in long telephotos. This effect is similar to what you see when using a telescope or binoculars.
The further away the subject is from the camera the longer the DoF will be.
The aperture adjusts the DoF. The wider the aperture is the shallower the DoF. The narrower it is, the longer the DoF.

The DoF is distributed both in front and behind the plan of focus. The generic model of this distribution is one third in front, two third behind. This is not quite true. Some lenses are very nearly 1:1. You need to test your lens or do some DoF related search on your particular equipment.

Since the DoF transitions to out of focus not all of it is usable. The acceptable field of focus is the used, as a DoF' subset and can be considerably shorter both in front and in the back.

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Mar 27, 2021 21:16:47   #
Rongnongno Loc: FL
 
ETTR
Expose to the right.

This works only if you shoot and use the raw format.

When a camera processes the sensor data using the Bayer filter it uses the RGBG sensor data. This means the raw file is... Green, dark green. When processed the camera produces correct JPGs that are not only color corrected but also brighter.



So, what is going on really?
If you look at the camera histogram you see a histogram that is great for a JPG file but completely off base for a raw file. The result is that you have to over expose in order to get a correct exposure for the raw data. Basically moving the JPG histogram to the right and destroy the JPG in the process.

What are the advantages of using ETTR?
 ► preserving more details in the highlights
 ► reducing the sensor noise in the dark
 ► exploiting the camera sensor's DR

One simple solution to get a 'true' histogram from a jpg is to use a special white balance called uniWB (Unitary White Balance). This works only when shooting raw. Any JPG produced in camera as in shooting raw+JPG will be worthless.

Rmalarz full explanation of what ETTR an EBTR are.

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Mar 28, 2021 07:07:12   #
Rongnongno Loc: FL
 
F-Stop

F-Stop stands for Focal length Stop (Theoretical value) Another definition cites Field length value.
F-Stop is nothing more than a number in the aperture scale.

The lowest the number the wider the lens is open, the shorter the DoF is
The higher the number the narrower the lens diaphragm is closed, the longer the DoF is

The lowest and the highest number on the scale depends on your lens.

Lens with an aperture as low as F-stop as F-1.1* and higher as F-32 exist, just not on the same lens...

Please read Aperture for more information.


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* Voigtlander Nokton 50mm f/1.1 Lens. The same company,Voigtlander, makes 0.95 lenses.

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Mar 30, 2021 08:02:57   #
Rongnongno Loc: FL
 
Depth of Focus

Depth of Focus refers to characteristics of the projected image inside the camera at the location of the film or digital sensor.

While this is out of the photographer's control it is interesting to know.

Comparing to the Depth of Field...
 ► DOF is in front of the camera (Scene)
 ► DOF is variable
 ► Depth of Focus is inside the camera (Sensor array)
 ► Depth of Focus is influenced by the F-stop, but the sensor focal plane stays static.
 ► Depth of Focus is dependent on the lens curvature

The softening and diffraction present in the corner edges in an image is due to projection passing the limits set by the Depth of Focus. Only a reverse spherical cap matching the lens can insure full accuracy.

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