Saturday, September 13, 2014

Core elements - Digital Photography

To the beginners and enthusiasts of photography out there, I would like to get you started with the basics of more serious photography than shooting in AUTO all your life, which can prove to be a great start to build your Taj-Mahal or an Eiffel Tower of photographs.

I have tried in this post, to break the technical details of photography in to easily understandable English. The information in this post are based on my knowledge and experience on the subject, and verified information I found on various websites, all collated and differentiated in to two parts to make it easier to understand.

Since I use a Canon system, I won't be mentioning about Nikon or any other camera system(s) (unless necessary) in this post.

Quick Note: (The images with "Avinash K", "Avinash Krishnamurthy", and "Feast For Your Eyes" watermarks on them are my proprietary work)


PART 1:

A) INTRODUCTION TO "APERTURE":
When you open the lens cap, you are allowing the light to flow in to the camera through the lens, but there are two checkpoints those light rays will have to cross before they reach the sensor - "Aperture" and "Shutter".

A series of retractable metallic blades arranged in circular fashion form an Aperture (as shown in the images below), and they are placed in such a way that they collectively offer the photographer a very effective way to regulate the amount of light that travels ahead towards the sensor. It does so by closing to restrict light, and opening to allow light.

In "closed" state, the aperture lets in very less amount of light to pass through it, unlike when it is wide open. Aperture, when "wide open", lets in the maximum amount of light.

Aperture in a lens
















Much closer look of Aperture
(Image source: N/a)























Depending on the type of camera and the lens used, the aperture can either be controlled manually (electronically), or automatically (controlled by the camera), or both ways separately. Initially, aperture rings were added to the lenses in order to physically control the aperture, but they got a major make-over as the years passed and technology improved. Basic "point and shoot" cameras are very portable, cost effective, easy to use, but they often lack manual controls.

Aperture can be controlled by changing the "f-stop" AKA "focal-stop" on the camera, which is denoted by the letter "f" (lower case).

Eg:// f/1.8, f/2, f/2.8, f/3.5, f/4, f/5.6, f/8.0, f/16, etc.

Formulas:
1) Focal length divided by the lens diameter = f-stop
2) Focal length divided by f number = Lens diameter

Graphical representation on how Aperture works



Lower the f value, larger the aperture (more light enters the camera)







Focal length:

Focal Length is not a measurement of the actual length of the lens. It is the calculation of an optical distance from the point where light rays converge (or diverge) to form a sharp image of an object to the sensor at the focal plane in the camera. When the lens is focused at infinity (farthest object(s in focus), its focal length is determined. Focal length is measured in "mm" - millimeter.

Eg:// 18-55 mm, 50 mm, 70-300 mm, etc.

When focusing the lens to infinity, make sure the aperture is set to higher f values in order to reduce the blurring of foreground.
Graphical representation of "Focal Length"




















Focal length and Aperture:

When the focal length is increased, the aperture reduces**, thus reducing the amount of light reaching the sensor.

** = Aperture value remains constant only when lenses with fixed aperture are used.




Understand your lenses:
Telephoto Zoom lens
Focal length = 75-300 mm (variable),
Aperture  =  1 : 4 - 5.6










In the above image, the ratio "1:4 - 5.6" refers to the widest aperture available for the lens. It means, the lens can be opened up to "f/4" at the widest end - 75 mm, but only "f/5.6" at the longest end - 300 mm. In this case, the amount of light reaching the sensor will be reduced by 1 stop when the lens is zoomed in from its widest end to its longest end (from 75 mm to 300 mm). At any given point, its aperture can only be decreased below f/5.6, but cannot be increased beyond f/4.

Prime lens
Focal length = 50 mm (fixed), Aperture = 1.8











Commonly used lens types:

Prime lenses - have fixed focal length, and are considered to be the best lenses to shoot with because of the sharp images they help produce. They are constructed with fewer internal elements as opposed to zoom lenses, which helps them with better light handling - as a result, sharper images. Beginners may find it hard to work with prime lenses because of the lack of zoom, and one needs to do a lot of moving around to get the right frame.

Zoom lenses - variable focal length on zoom lenses makes them the preferred lenses for most events. Variable focal length helps when you need wider angle, and also the "reach" by zooming - without having to change the lenses for the same purpose (on DSLR cameras). Zooming in narrows the angle of view, but gives you the much needed magnification of your subjects when needed.

Magnification achieved by a zoom lens at various focal lengths
Lens: Tamron EF 70-300 mm



















Multiple elements are involved in the construction of lenses, which makes way for errors like Chromatic Aberration(eg:// Color fringing), front focusing, back focusing, etc. Controlling lens errors is a complex but very important process for lens manufacturers.


Angle of View (AOV) -  is the angle of the subject area that is projected to the camera's sensor by the lens.

Field of View (FOV) - is the measurement of the subject area at a given focal length.

Varying focal length / aperture varies the angle of view / field of view.

The subtle difference between the Field of View and Angle of View





















B) INTRODUCTION TO SHUTTER:

In photography, the Shutter is the last checkpoint for the light entering the camera before it reaches the sensor. It remains "closed" by default (except while video recording), until we click a photograph by pushing the shutter release button down completely. Point the camera towards you and try to see its sensor through the center of the lens. It is not possible to locate it because the shutter blocks its view. Now push the shutter button all the way down in order to see the shutter in action, and pay attention to it, as it is happens very fast.

The "snap" sound you hear on your camera as soon as you push the shutter release button down completely is made by the shutter in one shutter cycle. The Shutter controls the duration of light that passes through the aperture. Hence, the longer it remains open, larger the amount of light the sensor receives.

Electronic Shutter
















Mechanical Shutter on a film camera
(Image source: mikegrigsby.com)























Digital cameras now use electronic shutter, and like everything else, shutters have a history too. Depending on the shutter speed set, the shutter remains open either for several minutes, seconds, or for less than a second. The values are represented in "seconds".

Eg:// 30", 20", 10", 5", 1/500 sec, 1/2000 sec, 1/4000 sec, etc

X" = X seconds (for low light / night photography. Use tripod to avoid shaky images.)
1/X sec = Xth of a second (fast shutter speed / high speed shutter for moving or/and very bright subjects)

Click here to know more on Shutter.

Merry Go Round on a spin (Slow shutter speed - 1/2 sec)















Long Exposure (Shutter speed - 2.5 sec)


Drop by drop (Fast shutter speed - 1/250 sec)



















Higher the value, faster the shutter speed, and quicker the capture.



Metal birds, against the Sun (High speed shutter - 1/3200 sec)





















C) INTRODUCTION TO "ISO":

ISO is the level of sensitivity of your camera to available light. Every digital camera comes with the most important (also the most expensive) part called "Image Sensor" or "Sensor" (in short). Changes in the ISO value decide how sensitive the sensor is to the light that falls on it. Lower the ISO value, less sensitive your camera is, to light.

The sensor gathers the light that falls on it, and transforms that data in to corresponding image. Increasing the sensitivity helps the camera capture images in low-light conditions without other external light sources, but at the cost of "grains" / "noise" in the images. Higher the ISO value, more grainy the image gets. ISO plays an important role in determining the optimal shutter speed and aperture value for a scene, to get the right exposure for your images.

All cameras have a "Base ISO", which is the least ISO number that produces the highest quality image without adding noise (grains) to it. While it may be ISO 100 on some cameras, it could be ISO 200 on others. It is best to figure out the Base ISO value and stick with it as much as possible in order to obtain the highest image quality at all times. However, it may not be possible to shoot with base ISO at all times, as shooting in low-light / dark conditions require you to crank up the ISO value. Use of flash certainly helps keep the ISO low in such situations, but it's ones personal choice whether to use it or not.

ISO numbers typically start with 100 and may go up till 3,200 on older / basic digital cameras. On some Semi-professional DSLR cameras, it can reach as high as 25,600. The ISO numbers start from 100 and its value increments in the power of two; i.e., 100, 200, 400, 800, 1600, 3200, 6400 etc. Increment of every step doubles the sensor's sensitivity to light. It is believed that using the ISO values that are obtained by the base ISO to the power of two produces the least amount of noise in the images as opposed to the in-between values that can be set.


High ISO value = higher shutter speed




















As we can see in the chart above, increase in ISO speed reduces the exposure time, thus allowing us to increase the shutter speed. Similarly, decrease in the ISO speed increases the exposure time, thus reducing the shutter speed.

Below is an image I shot on my Canon EOS 60D camera, using my Canon EF 50 mm f/1.8 II lens, at ISO 12,800 (highest ISO the camera allows) at around 7:30 PM under extreme low light condition. Due to the amount of noise the camera produces at such high ISO, the image looks almost unusable. Unless the shot was really necessary, and there was absolutely no light source available, it would be pointless to crank up ISO to these levels.

ISO - 12,800, Shutter Speed - 1/13 sec, Aperture - f/2, Tripod - not used


















Professional DSLR cameras of this age have highly refined "High ISO Noise Reduction" capabilities, that can produce noise free images even at high ISO levels.



PART 2:

It is now time to understand how each of the above discussed aspects affect the final outcome of a photograph.

Understanding EXPOSURE:
A photograph's exposure determines how light or dark an image turns out when captured on a camera. The term "Under-exposed" describes an over-all dark (black) image, and the images are "Over-exposed" if too bright and the details appear washed out. These terms are not limited to over-all exposure of the images, as the part(s) of images can be over-exposed or under-exposed.

An example to show how various exposure levels affect an image


















Aperture, Shutter Speed, and ISO - combined, they determine the exposure of an image! This is called "Exposure Triangle", the graphical representation of which is available below.

Exposure Triangle
(Image courtesy: exposureguide.com)



















As discussed above, Aperture regulates the amount of light that enters the camera, Shutter speed controls the duration of light that falls on the sensor, and ISO controls the sensitivity of your camera's sensor, to light.

Therefore, one can control the exposure of an image by altering any one or all of those settings, but the key is to learn how to compensate the changes of each settings with the other settings in order to get the same exposure. It is important to know that each setting has influence over the other settings.

I found a great deal of exposure related information on this website. Go through it for more in-depth understanding of exposure.


DEPTH OF FIELD (DOF):

There are several correct definitions to what Depth of Field actually means, including the ones below:
  • It is the amount of distance between the nearest and farthest objects that appear in the acceptable range of sharpness.
  • The zone of acceptable sharpness is referred to as Depth of Field. Thus, increasing the Depth of Field increases the sharpness of an image in the focused area.
There are two ways to describe the quality of the DOF:
1) Shallow DOF
2) Deep DOF

Shallow DOF is when the included focus range is very narrow - a few inches to several feet. Deep DOF is when the included range is several yards, to infinity.

DOF is directly proportional to the size of the Aperture. Lower Aperture values produce higher depth of field, making the subject in focus more prominent in an image. Lower the DOF, flatter the image looks (less background / foreground blurring).

NOTE: Change in focal length changes the depth of field as well.

The following image shows how DOF varies with changes in the Aperture:
f/5.6  and f/8 = Shallow Depth of Field
f/22 = Deep Depth of Field
(Image source: uglyhedgehog.com)




























More examples:
Gears (Aperture = f/1.8 at 50 mm)
Praying Mantis (Aperture = f/5.6 at 55 mm)


Bride (Aperture = f/5 at 135 mm)








































Deep Aperture (f/22 at 55 mm)























If you wish to get in-depth information on Depth of Field, click here.


Camera on-screen readings:
In this final section of this post, I would like to show you how to read the valuable data on the view-finder / LCD of your digital camera which is like our guiding light in total darkness. No matter how differently various cameras display the data, the basic components remain the same.

Quick settings menu on a Canon DSLR's LCD


















Legend (from the top row):
M = Manual Mode (displays what mode the camera is in)
1/125 = Shutter Speed (exposure time)
F5.6 = Aperture (displays the aperture value)
ISO = AUTO (can be changed, except when the camera is in full AUTO mode)
-3 . . 2 . . 1 . . (0) . . 1 . . 2 . . +3 = Exposure scale (in stops). Maintain this at "0" or at the center, for proper exposure. More to the left is under-exposed and more to the right is over-exposed


EPILOGUE:

If you use / own a DSLR already, great! Some compact digital cameras provide a few manual controls if not all. Those of you with one such camera should be able to locate any, or all of the following modes on the camera's mode dial:

  1. P (Program)
  2. Tv (Shutter Priority)
  3. Av (Aperture Priority)
Typical Mode Dial on a digital camera












They collectively fall under the "Creative Zone".

If you found even one of the above listed modes, simply turn the dial to that particular "semi-automatic" mode and play with different settings to obtain interesting and surprising results.

I know most of us are not habitual of going through the instruction manual of a product that is new to us, but I highly recommend going through the respective instruction manual to understand the settings better, if you aren't already familiar with them.

Happy clicking!

This is my first ever post on photography, and I know it won't be perfect. If any of you notice any in-consistencies in the post, please leave a comment, so that I can make the necessary changes.


Continue reading: Creative Shooting Modes (Creative Zone)

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