Wednesday, April 17, 2013

Photography - Frequently asked Questions - Camera

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This FAQ is aimed at people who have a point and shoot camera or a digital SLR and want to take good photos.  This is focused on Digital still Photography. What this means is that we will not be talking film.  Please note that this FAQ is work in progress. Based on queries, this will be modified.

This FAQ is supposed to do two things. Primary purpose is to give an introduction on the variables a person has to be aware of, to have a good control  over his camera (Note: this is a necessary, but not sufficient condition to make you a good photographer). The secondary purpose is to help me understand what my knowledge or lack of it is. 

"Photography is part science and part art". The problem is that most of the time we don't know which is what :-) And i don't promise that this FAQ will answer this question. But it may help motivate you on a journey so you can answer the question yourself :-)

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What is a Camera?
A Camera is a device that captures light on to a sensor. The sensor can be a CCD or a CMOS or a film.

How does the sensor capture light?
The sensor does it with the help of a lens. The purpose of a lens is to focus the light from the object of interest ( called subject) on to the sensor. the lens is the key part of a camera, more important than the camera body.

What is the purpose of the shutter ?
Shutter determines the duration light falls on the sensor. Shutter speed is measured in seconds. Depending on the camera, this can be as fast as 1/8000 of a second. 

What is the purpose of fast shutter speed and slow shutter speed?
Fast shutter speed freezes action. Slow shutter speed helps to blur action.  Point to be noted here is that fast and slow shutter speeds are context specific. A hummingbird that flaps it wings 80 times a second needs a different shutter speed to freeze action compared to race horse.

What is this Aperture or f-stop?
The apperature is the opening through which light passing through the lens is allowed to fall on the sensor. The opening can be adjusted, different opening sizes are given different numbers and the larger number means smaller opening.

Is this f-stop important?
It is very important since f-stop determines how much light falls on the sensor.  Smaller the number, more the light that falls on the sensor. The most common f-stops are f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, and f/22. This is also called  full f-stops. 

Is there a definition for this f-stop?
This is defined as the ratio of the lens's focal length to the diameter. This (dimension less number) is a quantitative measure of lens speed and an important concept in photography.

For the more math oriented people: Modern lenses use a standard f-stop scale, which is an approximately geometric sequence of numbers that corresponds to the sequence of the powers of the square root of 2:   f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45, f/64, f/90, f/128, etc. 

My DSLR camera has lot more f-stops than mentioned above. Why?
Most of the point and shoot cameras and Digital SLRs use what is called 1/3rd stop f number scale that goes on like this. f0.7,f0.8,f0.9,f1.0,f1.1,f1.2,f1.4,f1.6,f1.8,f2.0 ,f2.2, f2.5, f2.8, f3.2, f3.5, f4.0, f4.5, f5.0, f5.6, f6.3, f7.1, f8.0, f9.0, f10.0, f11.0, f13, f14, f16, f18, f20,f22
So depending on how advanced your lens is, the f-stops available to you keep changing.  

How is the f-stop written? i see a f/4 and f4. are they different?
No. f/4 and f4 are the same. f-stops are either mentioned using the notation, with f in italics; f/ or f - followed by the effective f-number.

What is this ISO thing?
It is an unit to let us know how sensitive the sensor is to light. Higher the ISO number, more sensitive the sensor is  to light. 

So technically, what does it mean to take a photo?
It means that we have to choose a f-stop, shutter speed, and a sensitivity good enough to capture an image of  the object of our interest.

How does this Shutter, Aperture and Sensitivity all come together?
Assume that you have a bucket that needs to be filled with water. Sensitivity can be equated to the volume of the bucket. More the sensitivity, less the volume.Shutter speed can be equated to the duration of water flow. Aperture or f-stop can be equated to how fast or slow water flows. Assuming the same duration (time) of water flow, If water flows very fast, the bucket will fill in sooner compared to slower speed of water. This relationship holds under reasonable limits.

What is exposure mode?
A combination of shutter speed, aperture, ISO and a few other parameters is called exposure. How the parameters are set determines the exposure mode of a camera. If you look at your camera, you will see something like AF, M, A and S. These are usually the typical exposure modes available other than a few customized modes.
AF - This means auto focus. The camera takes care of everything. the user has to click.
M- This means Manual . The user sets everything ( shutter speed, aperture, ISO and a few more parameters).
S- Shutter Priority. The user chooses a shutter speed. Camera decides the rest of the parameters.
A - Aperture Priority - The user chooses an f-stop. Camera decides the rest of the parameters.
P - Program Mode - The user chooses and f-stop, shutter speed and rest of the parameters. This is useful when you shoot indoor or locations where you know how the lighting will be.

I don't find the letters as mentioned above in my camera. Why ?
Even if the letters don't match exactly in your camera, they will be there under some other letter. Read your camera manual :-)

Why is this exposure mode important?
Because Exposure modes change how parameters like shutter speed, aperture and a few others are chosen.

What is the advantage of lower f-stops ( like f1.4, f1.8, f2.0, f2.4,...)?
Lower the f-stop, the camera will handle low light better - without the need of a tripod or additional lighting. 

Why?
Because lens with maximum aperture of f2.0, f1.8 and f1.4 allows more light to come through, opened up. These are also called fast lenses.

Why are these lenses called fast lenses?
These are called fast lenses because they allow us to shoot with higher shutter speed. and there by freeze action or shoot hand held in low light.

Take the example of two lenses. a lens with maximum f-stop of f2.0 and another with an f-stop of f2.8. Say we are shooting an sports event , where we want to freeze the action. When we use the f2.8 lens, assume we have to shoot at 1/1000 of a second. If we use a f2.0 lens, we can shoot the same  event at 1/2000 of a second. 1/2000 of a second is faster compared to 1/1000 of a second and this is the reason why a lenses with lower f-stops are called faster lenses. because you can use a faster shutter speed ( in a relative context). While the user may not think too much about it, when having to use a lower shutter speed in a low light scenario without the aid of a tripod, the lens with a maximum f-stop of f2.0 will allow us to shoot the event with the camera hand held while the f2.8 lens may mandate the use of a tripod. And if you don't have a tripod, you will end up with a shaken image. 

When do i use a Tripod?
Experience will let you when to use one. The Thumb rule is that if you are using 30mm, any exposure more than 1/30th of a second will need a tripod. that is 1/15th of a second and more will need a tripod. It also depends on how steady the photographer's hands are. Fast lenses will minimize our dependence on tripod.

So should i always go in for a fast lenses?
If you can afford to buy and if you can afford to lug them around. These lenses are quite expensive and also quite heavy.  Take the 18-55 lens that i have for my Nikon D80. It only opens up to f3.5 at 18 mm and up to f5.6 at 55 mm. f3.5 or f5.6 is not a lot open compared to say a f2.0,  but it is lighter, easier to carry and also affordable. Also, notice that you don't always get the sharpest images with your lens wide open.

How different is the lens carried by the professionals to , say for example the 18-55 Nikkor you mentioned above?
Unlike the zoom mentioned above, a professional zoom  lopens up to the same f-stop at 24mm and 70mm. It is also expensive. Nikkor 24-70mm f2.8 lens costs around 1700 $.  

So,  if it is that costly, don't i have a choice? 
There is. Nikon and Canon have the fixed focal length lenses called Prime lenses. These are available in 28mm, 35mm and 50mm focal lengths and also at f1.8. These are fast lenses and very much affordable ( relatively speaking, compared to a professional lens). 

Does f-stop decide the sharpness of the image?
Yes. Picture sharpness varies with f-stops and the optimal f-stop also varies with the characteristics of the lens used.  For modern lenses the sharpest image is obtained around f5.6 - f8.0. That is why photojournalists have a saying f8.0 and Be There (http://www.adorama.com/alc/article/13109).

What is this  Normal, Telephoto and wide angle Lens people talk about?
A so-called normal lens roughly approximates the perspective, though not the area of, a scene seen by one human eye. By convention a normal lens on a  full-frame digital SLR has a focal length of 50mm. Anything less than 35mm is wide angle and less than 24mm is ultra wide. Also any focal length greater than 70 mm is called telephoto. Note that all these focal lenses are in reference to a full frame camera. In case of  digital SLRS that have a lesser sensor size ( Nikon DX cameras) to get a coverage equivalent to a  50mm (full frame reference) on a DX camera (crop factor 1.5), we need to use a focal length of  34 mm (i.e. 50mm/1.5) 
Is this ISO thing still relevant today?
Yes. Very relevant. Unlike film with digital cameras, you can set the ISOs  for each shot. And the maximum ISO some of the DSLRs can be set is as high at ISO102400 (Nikon D4, Canon 5D Mark III)

What is the normal ISO setting i should use?
Try Auto ISO option in your camera. The camera decides the ISO setting for you. Usually set it to ISO100 or ISO 200 for sharp and less grainy pictures.

When do you increase the ISO and for what?
When you want to freeze action under low light, you can use higher ISO setting in your digital camera. But the picture will be more granular. Alternately, for people who want the grainy effect in their photos (it reminds them of the older day photographs) the ISO can be increased. Just try and play with your camera and decide for yourself :-)

shallow depth of field
Why is that the images of people seen on magazines look so nice and many a times, the background is completely blurred and beautiful. What is this ?
There is something called 'Depth of Field'. It is defined as the distance range in which objects appear clear and sharp. Adjusting this allows for a photographer to control which objects appear in focus, and which do not. A photograph that starts sharp with nearby objects and stays sharp into the distance has a lot of depth of field. An image with a very narrow band of focus is said to have shallow depth-of-field. Shallow Depth of fields are preferred in portraits and close up shots. This is achieved by using a large f-stop (smaller f number) - refer the flower. This is also aesthetically pleasing. Large DoFs are preferred in Landscapes and this is achieved by using an f-stop that is as small as possible.


How do i get the same effect with my camera?
It depends. We have to understand that many of the photos you see in magazines are staged. that is the light that falls on the subject and the angle at which light falls are all stage managed. They also undergo lot of post processing. So getting the same effect with a Point and shoot may not be possible.  We need to understand the limitation of the device that we use. Most of the time, most of the devices that we use are good enough. But not all the time.

So does DoF depend only on f-stop?
No. The depth of field of an image produced at a given f-number is dependent on other parameters as well, including the focal length, the subject distance, and sensor size used to capture the image. With devices that use a smaller sensor (like a mobile phone camera), the DoF is always high.

What is Bokeh?
In photography, Bokeh is used to describe the blur or the quality of the blur in the out-of-focus regions of an image. This can be achieved by taking pictures with a shallow depth-of-field. They can become prominent and, even though out of focus, very important part of a shot.

You talked about Sensor Size. Is it different in different cameras?
Yes it is. The baseline for comparison is the 35mm film size.  A full-format sensor (24 x 36mm) is equivalent to a frame of 35mm film in size, and these sensors are very large and expensive. They are found in flagship DSLR models  (
Canon's 1Ds/5D and Nikon D3 series are the most common full frame sensors.).

Canon cameras such as the Rebel/60D/7D all have a 1.6X crop factor, whereas mainstream Nikon SLR cameras (D3100, D3200, D7000 and D7100) have a 1.5X crop factor.   

Point and shoot cameras sensors are much smaller compared to a 35mm film size and phone cameras smaller than point and shoot cameras.

What is this crop factor you mentioned above?

It is the ratio between the diagonal of a 35 mm sensor to the diagonal of the sensor in use. CF = Diag ( 35mm)/Diag (reference). This ratio is also commonly referred to as a focal length multiplier ("FLM") since multiplying a lens focal length by the crop factor or FLM gives the focal length of a lens that would yield the same field of view if used on the reference format (35 mm film)

For example, a lens with a 50 mm focal length on an imaging area with a crop factor of 1.5 with respect to the reference format (usually 35 mm) will yield the same field of view that a lens with a 75 mm focal length will yield on the reference format.

Is the sensor size important and why?
Yes. It is. To put it simply, with a larger sensor, we are able to capture more light. It will also have less noise.  With a small sensor, the pixels can’t capture as much light, so a pocket camera will produce images that have less dynamic range and never as clean as a DSLR. exceptions are the latest cameras that are point and shoot, but also have a DX sensor (Nikon coolpix A) or Sony RX-1 ( full frame sensor).

What is White Balance ?
Flourescent lighting adds a bluish cast to objects whereas tungsten ( incandescent bulbs) lights add a yellowish tinge to objects. We don't generally notice this because our eyes adjust automatically. So unless light is very extreme, a white paper will generally look white for us. [Human eyes see differently compared to cameras. more on this point when we discuss composition]

Since a digital camera is not smart enough to make these adjustments automatically, we need to tell the camera to do it. White balance is the option provided by cameras for this purpose. Different cameras have different ways of adjusting white balance, so you have to check your camera's manual to know how to set this.

What option do i set it to?
Choose  AWB (Auto White Balance) mode. This is good enough for most of the shots you will take.

Does AWB has its own limitations?
Let us consider a sun rise or sun set or any of those scenarios where we see dramatic colors. Camera’s white balance system has no way of knowing that a sunrise or sunset is supposed to have a warm color cast to it. It just sees that all the neutral tones have color in them, and so it removes some of that color and takes some of the life out of the scene. So using AWB when shooting sun rise or sun set is clearly not advised.

AWB can also be inconsistent. When using a telephoto lens and zooming from wide to telephoto, the AWB setting out put will not be consistent as the camera may think that the colors have changed.

But is there more to this white balance?
The light has a certain temperature associated with it, measured in Kelvin (K). Sunrise and sun set is measured at 3200k,  sunny day light around noon is measured at 5500K. Knowing this information helps us to reproduce color as close to reality as possible.  The other side is that by changing the temperature, the colors change, giving scope to creativity. 

How do i get a hang of this ?
Your camera comes with a certain pre-defined settings. check the manual for WB settings. Use a still object, indoor, lit with artificial lighting, without using flash. Try  compose shots with different WB settings and see how the colors change. Once you  are comfortable with this, you are requested to try this outdoors and repeat the same experiment with a different object. Outdoor means people don't  have much control on lighting. See how the image color changes with different WB settings. Try to get the original color as seen by our eyes and also try to introduce different colors. Keep practicing. This alone would give people the confidence to  step out of the AWB comfort zone.

What is this exposure compensation?
When we are not happy with the exposure option chosen by the camera, exposure compensation allows us to tweak the exposure values slightly.

Where do i see it in my camera?
In most digital cameras, it is usually indicated with a "plus/minus" sign and a sliding scale, usually ranging from -2.0 on the left to +2.0 on the right.  Moving the pointer ( which is at zero by default) to the left darkens the image and moving the pointer to the right ( +ve territory) lightens the image.

What about memory cards to use?
Check your camera manual to understand the type of cards to use.  There are two parameters we have to be concerned about in particular.

Rated Speed (e.g. 15MB/s, 30MB/s, etc.) is maximum speed of the card and also what you would expect to approximately see in typical usage of writing or reading files on the card. This measurement is very relevant  to still photography, especially for taking pictures with high resolution and/or saving in RAW format where the files created are very large. The faster the card, the faster it can save the file and be ready to take another picture. You can really notice speed differences with high-megapixel DSLR cameras when using multi-shot burst mode.

Speed Class is a minimum speed based on a worst case scenario test. The Speed Class is more important for video mode or camcorders, where the device is actually saving a steady stream of data. Since many of the DSLRs come with video option, it is better to go for higher class number ( preferably #10).
Should i use a single card with large memory, say a 16 GB class 10  ? 
It is better to have 2 8 GB cards rather than a single card. This helps when cards fail. Do the math. Likelihood of 2 cards going bad at the same time is lesser compared to 1 card going bad. This is also the reason why some of the DSLRs have provision to take in 2 cards. The camera writes to both the cards.

What is JPEG?
Most of the P&S cameras and DSLR cameras store the image shot as JPEG. JPEG (Joint Photographic Experts Group) is a compressed file format designed to allow easy transmission of images over the internet and for lower volume storage. JPEG offers a range of compression to achieve smaller and smaller image file sizes.

What about image quality?
To compress an image file you must essentially throw away some information about that image, thus reducing its quality. Compression is applied on saving and, once the file has been saved, the discarded information cannot be retrieved.The JPEG file format is not the optimal choice for capturing digital images but, when captured simultaneously with an uncompressed format, allows quick and easy image preview.

So what is the uncompressed format available to us?
RAW is the file format and is raw image data as captured and recorded by the camera sensor. Please note that RAW is a file format for image capture only and images in RAW format have to be processed and saved to a file format like jpeg before it can be displayed.   You may think of RAW as equivalent of a film negative. It allows lot of scope for post processing. Since it is uncompressed, RAW is also larger in size compared to JPEG.

Most of the advanced point and shoot cameras and all DSLRs give the option to shoot in RAW and JPEG. It is suggested that your camera be set to record images in both RAW and JPEG. For sharing on web, jpeg file format is good enough.

1 comment:

  1. I appreciate your efforts in the FAQ. It was very helpful. Thanks :-)

    ReplyDelete

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