25 March 2012

Let's get technical - Its ok to get hyper

Don't panic - the title in no way refers to a psychological state of being; it refers to the concept of hyperfocal distances :). Now that we have spoken at length about the technicals of photography (aperture, shutter speed, focal length, depth of field, etc), I believe that the time is ripe to delve into this magnificent and magical funda of focussing in photography - the hyperfocal distance. This is the sweet, magical spot at which when you focus, the image seems to be in focus from some distance before that spot to infinity in the background. Have you ever wondered why despite the smallest aperture (for eg, f22) you are unable to bring all elements of a landscape shot into focus? The trick is to focus on this sweet spot!

Hyperfocal Distance
When the lens is focused at the hyperfocal distance, the depth of field extends from half the distance between the focus point & the lens, to infinity. This occurs at all aperture settings; you can get this effect even at the usual minimum f-value like f3.5 (you needn't push the dial up to f22 or anything remotely close to it). The hyperfocal distance differs on the basis of the focal length & aperture of the lens. For example, a 200mm lens could have the hyperfocal distance as 275 ft (hence the depth of field would range from 275/2= ~136ft to infinity) while a lens at 25mm could have it at 5 ft (dof ranging from 2.5ft to infinity). These values themselves would differ at different aperture values. As you must have inferred by now, you need to "know" the hyperfocal distance for each focal length beforehand. There are multiple options for you to be in the know of the hyperfocal distances, a few of which are listed below.

1. Using the distance scale on lenses
I think it's best explained through a video tutorial. There are many out there on youtube. See if get the gist of the depth of field scale (also called distance scale) that most lenses have on them, through this video tutorial. If not, ask & you will find many more in youtube.

2. Using tools/calculators
For android users, this app comes highly recommended - DOF Calculator. Amongst other features, it has a hyperfocal distance calculator which takes the focal length, aperture & camera model to reveal the hyperfocal distance for this set of parameters.


I am unaware of any such apps for windows or apple phones (not that they don't exist) and so have not written about them. 

If you want to, and if you prefer the old school methods, you can also calculate the hyperfocal distance with your trusty pen and paper using the hyperfocal equation which is primarily a function of  focal length & aperture. Don't get swayed by the simplicity of the equation - it needs detailed understanding of a multitude of fundas before you can grasp the equation in its entirety. I myself chose to fall back on the android app rather than lose hair over the equation :).

Yet another option is to simply print and carry a detailed chart/table of the settings and the resultant hyperfocal distances. One such chart is available in pdf format here.

See it to believe it!
Check out the below images to see the difference for yourselves. The second image seems like it is in focus from -∞ to +∞, doesn't it? That's the magic of the sweet spot :)
Without hyperfocal distance
Focused at hyperfocal distance

11 March 2012

Let's get technical - Wadda Focus!

Almost a decade ago, when I got my hands on the new kid on the block - the digital camera, a feature in it that marked a major shift from film-photography was the auto-focus (AF) mechanism. The camera has some  intelligent and sometimes bewildering intelligence in it, one such mark-of-a-genius trait being the AF mechanism. Have you ever wondered how the camera achieves such sharp focus effortlessly, while being equally stubborn at other times? In this post, let's look at how the AF mechanism works, thus moving a step closer to understanding your camera and avoiding embarrassing moments when it refuses to focus on your friends :)  

Types of Auto-Focus (AF) mechanisms
AF mechanisms are broadly classified as either ACTIVE or PASSIVE. In the former mode, the AF mechanism emits waves, infrared or infrasonic (like a submarine's SONAR) and gauges the distance between the lens and the subject. The passive mechanism is named as such because there are no signals sent from the camera to the subject for calculating the distance between the lens and subject; instead the AF software inside the camera analyses the image to achieve optimal contrast obtained at different positions of the focusing ring. Most of the contemporary cameras use the passive mode because of the problems inherent in the active mechanism.

Active Mechanism
There are multiple problems associated with the active mechanism, which are aggravated when you are not in control of the environment. 
  • Infrared interference: if the AF mechanism uses IR rays for calculating the distance, an attempt to focus near a halogen bulb or fire or a candle would throw the AF mechanism off balance.
  • Transparent surfaces: using SONAR for calculating the distance would ruin the focusing attempt, were a glass or windshield to be introduced between the camera and the subject since the sound waves would bounce off the glass instead of reaching the subject.

Passive Mechanism
The passive AF mechanism quickly changes the focus a few times and compares the contrast of the images obtained. Based on which focus setting offers the best contrast, the camera chooses that as the optimal focus. This is based on the fact that a sharply focused image shows higher contrast than a poorly focused image. Well, as true as that maybe, only a genius could have tapped into such an obvious fact and used it as a means of focusing. Hats off to such Einsteins!

So why doesn't my camera focus?
If you understand the meaning of the term "contrast", then it is pretty easy for you to understand why the passive AF mechanism may act stubbornly at times. Contrast is the difference between the light and dark areas/pixels in the image. If the contrast is low, the image does not look rich in color; it looks dusty or dull. As you increase the contrast, the darker areas become darker and bright pixels become brighter. Also, given an illumination setup, the image shows best contrast when sharply focused.

Compare the low and high contrast images below. Note the difference in color levels and hence, the clarity of the image.
High Contrast Low Contrast
So if your camera is letting you down on occasions, check the below list and see if any of these is the reason:
  • The frame is almost uniformly colored: this happens when you try to focus on a clear sky, single-colored and uniformly lit wall or object. Since all the pixels have almost the same values, the camera cannot identify the contrast level in the image and hence cannot perform contrast based AF. In the below image, I tried to focus on a white wall but could not because of the lack of contrast.
White wall
  • Moving subject: this happens if the subject is in motion while you are struggling to focus on it. Since the pixels are moving, the 2 images taken by the AF mechanism for comparing contrast cannot be used for comparison. In this case, you are better off focusing on something that is at the same distance from the lens as the subject is, and then keeping the shutter half-pressed (the focusing happens when the shutter is half pressed), move the camera to get the subject in frame.
  • Low light conditions: less light means more dark areas. The darker the picture, the less the contrast (remember, contrast required dark as well as bright areas) which stresses out the AF mechanism. I was unable to focus in the below image for lack of visible light. As such, the superman logo is out of focus. (though it is bright red, lack of contrast and complete lack of visible light scrambled the AF mechanism).
Low light conditions

If you turn on the AF-assist beam through camera settings, in low-light conditions the camera will emit a bright light through an emitter on the front of the camera body (usually its next to the lens) which is used to illuminate the subject, thus increasing light levels and helping the AF mechanism focus. So enabling this option will help you use the AF in low light conditions. Some cameras allow the option of using the camera flash for AF - this is termed as pre-flash in which the camera emits multiple bursts of the flash to illuminate the subject while focusing.

AF Assist lamp

How does my camera focus?
If you are curious to know which AF mechanism your camera employs, you can try this trick. Go outdoors and point towards the sky and try to focus on it. In case of active AF, the camera will mostly focus but in case of passive AF, given a clear sky (no clouds and no variation in color), the camera will not focus.

Some tips about AF
The focusing mechanism offers two modes for you to choose from - continuous and shoot-only. Should you choose the latter mode, the camera will attempt to focus only when you press the shutter halfway. This is good and recommended for situations where you take time to compose the picture (portraits, studio shoot, landscapes, etc). During sports or high speed photography though, you may want to switch to continuous focus mode so that the camera does not wait for you to half-press the shutter to begin the focusing process, thus introducing a lag between shutter press and image capture. In this mode, the camera keeps attempting to focus the frame, regardless of whether you are tracking the moving subject or simply waving the camera around while waiting for something exciting to happen.

The continuous mode keeps the camera on its toes and hence, consumes more battery and leads to faster wear and tear of the focus motor. So unless specifically required, work with the shoot-only mode.

28 February 2012

Creative Explosion - Perspective

With this, I start a new thread of articles which explore creativity in photography. Until now, most articles penned by me have been restricted to the threads "Let's get technical" and "Blasting the myths" which dealt with laying down the technical fundamentals and clearing the mist around photography resp. Along the way, I believe I have chalked out a sound understanding of photography and laid the foundation for the next generation of posts.

Simplistically speaking, perspective is the spatial distance between objects in the image, that helps you judge the spatial placement/location of the objects and their heights/forms relative to each other. Perspective is affected by the focal-length & subject-to-lens distance combination. You can alter perspective by either moving around or by changing the focal-length of the lens or both.

A wider focal length creates more depth in the image (do not confuse this with dof) and makes the objects look farther away. A tele lens will make the objects look more closely located though in actuality they may not be, thus making the image look flat (less depth). I don't have an image to depict this phenomenon right now so I'll suggest that you visit this page to understand what I am blabbering about :)

How to alter perspective?
I'd say that more than focal length, it is the subject-to-lens distance that determines perspective. After all, change in focal length is an eventuality that follows when you change the distance. Unleash your creativity with perspectives by moving around the subject and clicking from various distances while maintaining the subject's height/width the same across images. You will notice that if you kneel down and click a standing person's pic from a close distance, the person looks gigantic as compared to his/her surroundings. This attributes a larger-than-life or a heroic feel to the persona of the subject. On the other hand, if you click the same subject by standing on a stool and looking down at the subject, he/she appears dwarfed, which creates a sense of suppression.

How perspective is used in movies
This is where the director of photography in movies/sitcoms comes into play. Using a telephoto lens, the director positions the actor far away from the lens. When the director zooms in on the actor through the telephoto lens, it looks like the oncoming truck is right in the actor's tracks and is going to overrun him when in fact, they are on parallel tracks made to look superimposed because of the manipulated perspective (zooming into an object from a distance flattens the perspective, thus making things look closer than they are). Also, when the director wants to show an actress/actor along in a dense area like a forest/garden, he uses a wide angle lens to introduce more depth in terms of perspective into the frame.

So choose a position because of what it does to the perspective; then choose the focal-length/zoom. The next time you click a pic, remember the "perspective" concept and put some thought into the composition of the image. I guarantee that you will like the entire process of photography even more down this road :)

26 February 2012

Let's get technical - Focal Length

If you own or plan to own an SLR camera, you would be exposed to the standard lens nomenclatures which define your lens' capabilities. Consider for example, the kit lens on most cameras - the 18-55 lens. In a Nikon you would come across the 18-55mm VRII f3.5:5.6 lens. In this article, we will discuss what the "mm" in the 18-55mm stands for and how it affects your clicks. Note that the focal length-range is also specified on the lenses of compact digital cameras.

Focal Length
In optics, it is defined as the distance between the vertical center of the focusing lens and the focal point. As can be deduced from the below image, closer the lens comes to the sensor (focal plane), lower the mm figure goes (focal length) and wider the image.

Image Courtesy: dptips-central.com
Crop Factor
Camera bodies are basically of 2 types - full frame and cropped sensor. In case of the latter, a cropping factor comes into play, which is somewhat equivalent to 1.3. So an 18mm wide angle lens on a cropped-sensor body will yield a focal length of 18 x 1.3 = 23.4mm. Hence, if you want to harness the real power of wide angle lenses, no cropped-sensor body will give you that like a full frame body would :)

Classification of lenses
Based on the focal length of the lens, it can be classified under one of the below categories:

  • Prime: this lens has a fixed focal length. For example, the 50mm f1.8 Nikon lens
  • Zoom: any lens that has a range of focal lengths (you can zoom in/out) comes under this classification. For example, 18-55mm f3.5:5.6
  • Wide angle: a lens that provides an eventual focal length of 35mm or below is called a wide-angled lens. Please note that in case of cropped-frame camera sensors (Dx in case of Nikon and APS-C for Canon), presence of the cropping factor means that your 35mm lens is not actually an 35mm lens and hence is not a wide angle lens.
  • Super zoom/telephoto:  with focal lengths beyond 135, a lens can be considered to belong to this segment.
The below snapshot is of a Nikon Dx 18-55mm lens. So the next time you look at a lens, I hope you won't be puzzled about the meaning of these golden colored letters :)
Image Courtesy: kenrockwell.com

Prime Lenses
If you are wondering why one would settle for a prime lens, which is no less expensive than a decent zoom lens, then I can answer that for you. A prime lens has lesser components as compared to a zoom lens (sometimes a zoom lens has upto 35 lens components in it) and hence have less negative effects on the image capture process. Due to multiple components in a zoom lens, the light entering the lens is reduced by the time it reaches the sensor. Also, zoom lenses work best at the mid-range; an 18-200 lens would would best at around 125mm while it would create problems like distortion at the extreme ends of 18 and 200 mm. Also, due to architectural provisions/restrictions, a prime lens can offer you a much wider aperture of 1.2 or 1.8 mm which is almost not possible in zoom lenses (most zoom lenses have a min aperture of f3.5). A focal length of 1.8mm yields a much shallower dof which is awesome for portrait photography.

In this image, do you notice the shallow dof? The face of the guitarist is in focus while even his hands which are quite near to his face are out of focus, not to mention areas farther away (the end of the guitar and the cushions). This was shot with a 35mm f1.8 nikon lens. If i were to shoot this with an 18-55mm even at f.3.5, the dof would have been much deeper and the focussed area would encompass more of the guitar, thus stealing attention from the guitarist and confusing it with the guitar.

27 January 2012

Let's get technical - Dynamic Range & Histogram

In statistics, a histogram is a graphical representation showing the distribution of data. In photography, a histogram shows the distribution of colors across the dynamic range of the camera or the color set of the image. Almost all cameras have a histogram display feature in them today, thus allowing you to judge whether your image is correctly exposed or not. To correctly understand histograms, you'd need to compare different images and their histograms. This post will simply help you understand what the graph on your screen says and whether you should listen to it all or not.

To understand histograms, let me first skim through the concepts of dynamic range and contrast ratio.

Dynamic Range
Each camera has a limit to the number of color/light levels that it can capture. This is called the Dynamic Range of the camera. Technically speaking, Dynamic Range describes the ratio between the maximum and minimum measurable light intensities (white and black, respectively). Let's try to understand this concept.

The sensor captures data in an analog form. This analog signal is then converted into a digital signal and sent to the camera's processor. Let's assume that the processor accepts an 8bit signal. So each pixel on the sensor sends out the pixel color/intensity information as an 8bit signal to the processor.

With 8 bits to represent each pixel signal, we end up with 28=256 levels of intensity within which this signal can lie. As shown below, a histogram in an 8bit digital camera shows the spread of different pixels between the darkest (0) and brightest(255) light intensities. Simply put, a histogram's vertical axis shows how much of the image is found at a particular brightness level. Here we can see that the image has more dark areas than bright. 

Coming back to the topic of dynamic range, a camera which uses more bits for encoding the analog pixel signal into a digital signal will have a wider bright-to-dark light spectrum and hence will capture colors more accurately at different light intensities.

Contrast Ratio
Some manufacturers or comparison websites express the camera's dynamic range with the term "contrast ratio". This number will look something like "1000:1". So how should we look at this concept?

Assume each pixel to be a bucket; a bucket that collects light photons. The more photons that a bucket collects, the brighter than bucket becomes. Now each bucket has a limit to the number of photons it can collect (and report to the camera processor). This depends on the number of bits used to convert the analog signal to digital. Let's assume the camera uses 8 bits which means the bucket can contain a maximum of 256 photons beyond which it will overflow (be overexposed). The lesser the photons, the darker the image.

Image courtesy: cambridgecolor.com
Contrast is the ratio between the brightness and darkness levels of the image. The lower the contrast, the more dirty/lacklustre/dusty the image looks; as you increase contrast, bright areas become brighter and dark areas become darker thus giving the image more clarity until a point beyond which the image starts looking unnatural. In the below image, starting from the lower left corner image (this image has the lowest contrast) you can see that as the contrast level is increased the dusty feel of the image starts wearing off and the image becomes more bright/sharp and clean. As we move clockwise towards the lower right image, the contrast levels have been increased too high to give the image an unnatural feel.

Image Courtesy: wikimedia.org
A contrast ratio of 1000:1 means the camera uses a minimum of 1 photon in a pixel to represent the darkest area as compared to a 1000 photons to represent the brightest area. The more the maximum number of photons that can be captured by the pixel, the larger the range of intensities that the sensor can capture. So a higher contrast ratio is always better since the camera will yield a higher dynamic range (provided the number of bits used by the camera for representing the light signal doesn't act as a limiter).

So to summarize, Dynamic Range/Contrast Ratio is the ratio between the maximum and minimum measurable light intensities.

How does dynamic range relate to histograms?
If you have accurately understood the point that I am trying to drive home, you may have realized that dynamic range forms the X-axis of the histogram - the range of brightness levels that the camera can capture :)
As the dynamic range increases, the width/number of intensity levels of the histogram increases and hence the graph becomes a more accurate representation of light intensities.

How does a histogram help?
There is nothing called a "good histogram". A histogram only tells you whether the image has too many pixels at a particular brightness/darkness level or if the intensities are well spread out. Knowing this helps you avoid posterization during post-processing and helps gauge whether the image is over/under exposed. How do you judge the below histogram?

Image courtesy: luminous-landscape.com
If you do not look at the image and only check out the histogram, your knee-jerk judgement would be that it is a bad image, won't it? :) But histograms are certainly useful, as can be seen in this post.

12 January 2012

Keep it RAW!

Advanced cameras can capture and save images in JPEG as well as RAW formats. Though RAW format consumes more carpet area on your memory card, it is wonderful and may I say, the only option for post-processing. Let's have a look at why JPEGs are bad for post-processing/image correction.

How does the digital camera create an image?
Your camera sensor senses the incident light along with its different aspects like brightness, contrast, hue, the colors in it and many other things and applies a sophisticated algorithm to process all this detail and save it as an image on your memory card. This image can be saved with a lot of information or with minimal information so as to reduce the file size. If you save all the information possible, you can then selectively remove/polish/modify selective aspects of the saved image in an image editing program to yield desired results. If you remove much of the information and retail only as much as required for the image to be created with near-to-real reproduction, then you would achieve a much smaller sized email image which you can't do almost any post-production on. The previous type of image is called a loss-less image (RAW for example) while the other type is called a lossy image (JPEG).

What is a JPEG?
JPEGs were created as a web-friendly solution for images. Before JPEGs came into existence, the world worked with BMP images (which are quite rare these days but if you had a windows 95 PC, it did not recognize JPEGs; you had to install special software to work with JPEGs) which is an acronym for BITMAP. In BMP images, each pixel's color information was saved in the file. So if you have 1024x768 pixels in the image and each pixel took x bytes to save, you'd end up with 786432x bytes for one image. I remember BMP commonly weighing between 4-10 MB each. You can't have such heavy images on a webpage!

Enter the JPEG! It's an acronym which stand for Joint Photographic Experts Group, the geniuses who used their mathematical prowess to revolutionize image persistence and shrunk the 4MB BMP to a 100KB JPG!

Because JPEG employs a lossy compression technique, every time you open a JPEG and save it through a CTRL+S, it is compressed and saved. So each save compresses it further and leads to a further reduction in detail. So if you want to photoshop your images, JPEGs are not the ideal solution even if you save them in the highest resolution possible.

Lay it RAW!
RAW is not an acronym - it simple hints at the fact that the image has undergone minimal processing between the point of capture (sensor) and point of save (memory card). As such, it contains maximum optical information possible. Each manufacturer has his own RAW file format which needs you to install manufacturer-specific software/drivers to view the RAW image. Nikon uses the NEF file extension while Canon uses the CR2 extension.

Why should I use RAW?
There are multiple reasons for which you should shoot in RAW provided you are adept at using post-processing tools like GIMP/Photoshop or any other sophisticated image editing software.
  • White balance correction: if you have shot an image with incorrect whitebalance settings, you can use a RAW editing program to make the correction. In the below image, the upper section has correct whitebalance while the lower one has a warm tinge.
Image Courtesy: phottix.com
  • Exposure correction: if you image is over/under-exposed, you can make corrections to get correct exposure. The below screenshot shows an over-exposed sky in the RAW image at the bottom with the corrected sky above it. This level of exposure correction is not possible in JPEGs.
Image Courtesy: kelbymediagroup.com
  • JPEGs store information in 8bit format while RAW store in 12 to 16 bit format which leads to an amazing difference in the quality of image detail. Due to this, any of the processing done to a RAW file yields a better final image as compared to changes done to a JPEG.
  • Many alterations/corrections like brightness, saturation, hue, contrast, color correction, gamma correction, sharpening, noise reduction, etc should be ideally performed on RAW images only.

Ok what's the catch?
With all due respect, RAW is not for everybody. Don't shoot in RAW just because I said it yields better and sharper images. If you don't intend to do post-processing on it, it's just not worth the hassle since you will be simply converting them to JPEGs for circulation/distribution and you personal archive anyway :p
  • RAW needs manufacturer specific drivers/software installed to read the RAW file. For example, windows cannot read the NEF file (Nikon). You can access it through Nikon's RAW software or through third party tools like Adobe Lightroom which is a RAW editing software.
  • File size: RAW files are typically 4-6 times the size of the biggest JPEG that your camera can save. That means 1/4th-1/6th the number of photos that your camera can save. So if your card can save a max of 100 JPEGs of the highest resolution, it can save less than 25 RAW files!
  • RAW process workflow takes up quite some time for even the simplest operations: if you shoot 200 images in your brother's wedding and need to load them in a RAW processing tool, make corrections to them and save as JPEG - you'd need a fast processor, multiple hands like a demigod and multiple screens on which you can execute this shit in parallel to get it done in one day! It takes me upto a week to process RAW images of one photoshoot!
  • And of course, you need sufficient knowledge about the RAW processing tool too!
 I shoot in RAW, process in Lightroom and then polish in Photoshop to finally achieve the desired JPEG. Each image takes anywhere between 45-90 mins. You don't need to treat each image with such tender care and loving but if you have that kind of patience, stay RAW!

11 January 2012

Let's get technical - Lenses

When it comes to selecting SLR equipment, one needs to pay acute attention to lenses rather than camera bodies. Camera bodies are much easier to compare and judge than camera lenses. To start with, we have multiple lenses in a manufacturer's stable which look alike. For example, you'd often find two zoom lenses with the same focal range but with one or two other characters in its name differing - let's suppose an 18-55 VRII and an 18-55 D(these are hypothetical offerings and may not actually exist). To add to the buyer's miseries there are third party manufacturers like Sigma, Tamron who also have their league of lenses which look similar in nomenclature and confuse the already nervous buyer. People often ask me or quiz the retail shop guy "why is this 18-55 lens by ABC thrice as expensive as the other 18-55 lens by the same manufacturer" and the quizee goes "its made of better material...its simply better". I'd say dumb retailer but would you like it if he hurled a barrage of jargon in your face and made you look like a dumb camera aficionado in front of the other customers? It's wise to just lie down and take such answers once in a while :) 

In this post, I will pour out whatever little I know about how 2 differently priced seeming-twin lenses could actually be different so as to justify the discrimination in price between them.

How a lens works
A camera lens has an array of optical lenses (you learnt about convex and concave lenses in school right?). The job of this lens arrangement is to focus the incoming rays accurately on the sensor. The accuracy of the lens greatly depends on the architecture(arrangement) of these lens elements and the materials that go into making these lenses. 

Image Courtesy: cambridgecolor.com
 ~ Building blocks: More than often, the price difference is due to the materials that are used to make these lens elements. For example, Nikon has this new technology that it has named "Nano Crystal Coating". I heard about this lens at a conference where one photographer thumped his chest and said "I finally bought a nano-coating wala lens" and all heads turned. By the time I turned around to see what the hulla was about, everyone had already prostrated in the direction of the now unanimously hailed sartaj amongst them :) Nano coating is some revolutionary low-refraction coating applied to lenses which reduces lens flare. So if you are shooting bright lights(like a street lamp or an oncoming car with headlights on) with such a lens, the glare cause by the bright light source will be quite reduced. This also reduces lens flares as shown in the below image. I borrowed it from Nikon's website which explains the Nano Coating funda. You can read up on it here. So if your lens has such a revolutionary coating, you can expect a pinch to your wallet.
Image Courtesy: Nikon.com
~ Image Stabilization: I have spoken at length about this feature in another post so I'll just mention that Canon uses the term IS (Image Stabilization) in its lens nomenclature while Nikon uses VR (Vibration Reduction). So if the lens is called 18-55 VR it means it has image stabilization mechanism in it and hence is higher priced as compared to a non-VR lens.

~ Chromatic Aberration & other cool/unwanted features: This is incorrect reproduction of colors due to the inability of the lens to focus incoming rays accurately on the sensor. Some lenses show obvious chromatic aberration in cases of high contrast or excessive brightness. Check out the below images. The one of the left is the one without chromatic aberration while the other has it. Do you notice the red border around the eagle's head? That is chromatic aberration.

Image Courtesy: cambridgecolor.com
Other problems that your lens can introduce you to are distortion, vignetting. Distortion is where the image does not seem to have been laid down on a flat pane. The below image is highly distorted - notice that the lines are not straight all through the image. The image has a bulging feel to it.
Image Courtesy: andrewwoods3d.com
Vignetting is the gradual darkening/brightening of the image around the corners. It is said that almost all lenses introduce vignetting to some degree though Nikon claims that one of its fisheye lenses (can't recollect which one) has no vignetting at all. The below image illustrates this effect.
Image Courtesy: wikimedia.com
So when a reviewer or a retailer labels a lens as a low-quality lens, it could be plagued by one or all of the above problems.

~ Lens speed: another very commonly used term to classify lenses is "fast lens". This simply means that the lens can take pictures at higher shutter speed owing to its wider  maximum aperture. For example, an 35mm f1.8 lens would be a faster lens as compared to an 85mm f3.5 lens since at f1.8 the lens is wider than it is at f3.5 and hence takes in more light and you can click an image of the same brightness with higher shutter speed or lower ISO.

~ Constant aperture: zoom lenses usually have a range of f values that it shuttles between as you zoom in/out the lens. The f-value of a lens is calculated by the below equation

f-value = focal length (mm) / actual lens aperture
In the cheaper lenses, the actual aperture of the lens diaphragm does not change as you change the focal length (by zooming in/out). As such, as you zoom in the f-value keeps increasing due to the above equation. Take the 18-200 f3.5-5.6 lens for example in the Nikon stable. If you set the aperture to 3.5 at 18mm zoom, as you keep zooming in towards 200mm, the aperture value keeps moving towards 5.6. So you can't achieve a f3.5 aperture at let's say 50mm or anything above it. Now there's no need to panic - there are special lenses made for perfectionists who will not bow down to this architectural flaw. These lenses achieve fixed aperture values because the lens adjusts the actual aperture as you change the focal length. For example, a 12-24mm f4.0 Nikon lens will not change its aperture come what may. Rejoice! But it will cost ya! :) 

There are other premium features like Canon's USM (ultra sonic motor) which produces very low sounds during operation. Such lenses are suited for wildlife photography where animals can get spooked by strange noises.

So you can see that to judge the correct pricing of a lens, one needs to be in the know of the above and many more paradigms that plague photography equipment and need you, the buyer, to either compromise and settle for low-performance options or to shell out the extra buck for improved performance.

10 January 2012

Let's get technical - White Balance

No smart-ass title this time because I am in a bit of a rush while I pen down this article :p Photography-workflow follows the age-old quality philosophy of 1-10-100. If you weed out an anomaly or unwanted element at the first stage you will need 1 unit worth of effort. If it is attended to at the next stage, the effort required multiplies ten fold! Often we ignore the camera settings while clicking a pic because of a repetitive consolatory voice in our head that goes "photoshop hai na" :) But when you have too many clicks from a photoshoot to edit, believe me, you'd wish that you had customized the camera's settings to avoid making simple corrections to images in photoshop at a later point in time.

What is white-balance (WB)
Having pointed that out, let me talk briefly on the subject on white-balance in photography. Please understand that your camera captures the light reflected from your subject, the light which has originated from a light source like a CFL or halogen bulb, or a tubelight or natural day-light. The natural daylight contains a spectrum of colors across the VIBGYOR range which combine to form the seemingly colorless light. Artificial light sources usually have a specific light color (also labelled color temperature) which is not very obvious to the human eye but greatly influences the camera sensor. Such artificial light sources, like ones mentioned above alter the white balance of the image with their color temperatures. For example, CFL lamps have a greenish tinge to their light - our eyes see these bulbs as bright white but the camera sensors sees the light as green; halogen/street lights have a deep orange shade. Also, if the subject is in the vicinity of a colored reflective surface like a shiny carpet/curtain/table then the light falling on the camera will contain that color and hence the whitebalance of the entire image will be screwed up.

This has bugged me often in weddings. There's a lot of sickening yellow in the air. Ladies don yellow colored sarees and drown themselves in an uninhibited display of gold. I hate it when I forget to correct the white balance on the camera - I shoot anywhere between 200 to 500 images which I later have to correct painstakingly in photoshop. It takes me even a week at times to make such simple corrections :(

So coming to the topic at hand, if your light source is artificial, you should click a test image and check if it correctly reproduces colors as seen by your naked eye. The color alterations are more evident in dark areas like areas in the shadows.

If you know the light source that is causing white balance alteration, you can choose from the below preset whitebalance modes.
Image Courtesy: cambridgecolor.com
What any whitebalance setting does it that it compensates for the excess of color in the environment. For example, the light source is flourescent, like CFL lamps, setting WB to flourescent will add light on the other side of the light spectrum to compensate for the excess flourescent light in the environment. So, if your scene is lit by incandescent bulbs, your light is orange. The Incandescent WB will cause your camera to add a lot of the opposite color, blue and cancel out the excess orange light, thus giving you an image that is closer to actual colors.

Preset White Balance

These are some common WB modes that you would find on cameras:
  • Auto – this works well in most cases but it's better to try the preset or custom mode for a mishmash of light sources.
  • Tungsten – use this in case of bulbs or high-temperature light sources. This mode produces a cooling effect which reduces the REDish light tinge in the image.
  • Fluorescent – this is the opposite of tungsten and warms up the image.
  • Cloudy – this setting generally warms up the image a bit.
Custom White Balance
In a situation where there are multiple light sources or too many reflective surfaces producing a non-standard whitebalance like tungsten/flourescent/cloudy, etc use the custom white balance feature of your camera. What you need to do is simply point out to the camera, the object/surface that is actually white. So what you are telling your camera is "see..this object is actually white but the light source is making it look blue/orange/green or whatever..". So the camera calculates the correction to be made to make that object look white under that light source and applies the same correction to all objects in the frame! Simple ain't it? :)

That's how simple the concept of white balance is folks! So the next time you are out shooting dozens of pics, please keep a checklist ready and include white-balance checks in it.

6 January 2012

Meter down

Thanks to my friend Rahul Purbey, an avid enthusiast, I got a new topic to write on - Metering. Due to his persistent queries, I had to do quite a bit of research on the topic and I think I have answer to his root query - "what is camera metering?".

Image Courtesy: my3boybarians.com
Camera metering is the funda that comes into picture once you have chosen the ISO, shutter speed and aperture. These three determine the exposure levels of the captured image - how under/over/correctly exposed the image is.

Metering can be inbuilt (most of us use the camera's inbuilt metering system) or external (the ones we see on tv, used in photoshoots wherein a person holds a metering device infront of the model's face to measure light). I am talking about the inbuilt metering system here.

Once you push down the shutter button and wait for the camera to focus on the subject, the camera performs the metering function and shows results on the lcd screen. The result is displayed by different models/manufacturers differently. In the above image, the metering result is shown along a horizontal scale (circled in red) with the center of the scale being perfect exposure (according to the camera's metering algorithm; camera metering is not always accurate) and either side being over and under exposure.

In the above image, it shows that the image is heavily underexposed(the meter shows readings on the -ve side of the graph) and hence, your image will be very dark if you use the current ISO+shutterspeed+aperture combination.

There are different ways in which your camera performs metering. The usual modes are spot metering, center-weighted and matrix/evaluative metering. Spot metering uses a spot on the frame to perform the metering process and determining whether that spot will be overexposed or underexposed. Center weighted metering, as the name hints, uses a small area around the center of the frame to perform metering. Matrix metering uses many more points spread out around the frame to perform metering.

So if you are concerned only about the rose in the frame and don't care if other elements in the frame get over/under exposed, use spot metering, and so on.

Its nice to put your grey cells to work while clicking a photo. Know the shutter speed, ISO and aperture settings and what exposures typical combinations provide. Also look at the meter before clicking. Look at it as a challenge - don't be a point and shoot user. Once you ready yourself for these challenges, you will actually enjoy and recommend photography as a hobby, instead of branding it as a piece of cake.

Happy clickin!

5 January 2012

Don't shake that booty!

I am a strong advocator of restraint when using flash for lighting; even if it is past sundown. I prefer to avoid the use of camera-flash altogether, as long as the subject is willing to stand still for those 5-10 seconds to avoid blur in the captured image. But keeping the camera steady for a speed less than 1/60th of a second (your camera will show this speed as 60 or 1/60 shutter speed) is nothing short of a herculean task considering that even in sufficient ambient light, blur begins to creep into the image below shutter speed of 60. So in this post, I will talk about some techniques that will help you discipline your body into standing still and reducing, if not completely eradicating camera shake.

The swan-elbow technique
This is a body posture that helps me steady myself while standing. Through practice I have near-perfected the posture over time. I call it the swan-elbow technique simply because it focuses on resting your elbow on your waist and in the attempt, you assume a pose resembling a meditating, relaxed swan.

Keep your feet apart such that you can stand without wobbling. The minimum distance would be that of the width of your waist. I was about to assume that you are a right-handed person and I realized - cameras are not made for left-handed people! Wow! He he..

Coming back to the topic at hand, you would be placing the camera body on the palm of your left hand and using your right hand for the shutter. Place the left elbow on your left waist. In the process, you will lean forward and your back will arch forth like the neck of a swan.

Now comes the difficult part. Learn to hold your breath. This is how snipers train. They learn to hold their breath and slow down their heart rate. A slow or soft beating heart leads to less tremors in the body and hence greatly reduces camera shake. Practice holding your breath in this pose and you will see that over a period of time, you can actually greatly reduce camera shake through this technique!

Also, keep your body comfortable - don't stress your muscles by extending your arms. Like your left arm, try to keep your right arm also close to the body. Be comfortable so that no part of your body feels pain/pressure/fatigue and leads to trembling.

The Lean Mean technique
No you don't need to slim down for this :p This technique simply hints at making apt use of solid structures to lean on them and stabilize your body to reduce camera shake. For example, instead of just standing and trying the swan-elbow technique, lean sideways on a pillar/column/wall, hold your breath and shoot - this is much simpler!

Put it down
Keep the camera on a stool or any elevated stable structure, look through the viewfinder and shoot. Though this will limit the angles that you can achieve (since the supporting object would have a flat surface), this will provide utmost stability to the camera unless you are standing on trembling ground.

So if you are not carrying a tripod around like a coolie, you can definitely work on the above techniques to get blur-free bright pictures in low-light conditions.

4 January 2012

VR / IS Lenses - should I foot the extra buck?

If you look at the brochure of any lens manufacturer, you will easily come across these VR (term used by Nikon) or IS (term used by Canon) lenses which seem to be similar to their counterparts without the VR/IS but are quite highly priced. For example, the Canon EF70-300mm f/4-5.6 IS USM is an IS lens as compared to the Canon EF75-300mm f/4-5.6 III. You can view these here. These are priced at INR 38,990 and INR 11,595 respectively. Though they don't have the exact same zoom range and USM is another differentiating feature between these lenses, I just used these near-siblings to exhibit the presence of lenses with/without IS.

What is VR/IS?
VR stands for vibration reduction and is the term used by Nikon. Its competitor Canon uses the term IS which stands for Image Stabilization. In either of these technologies, the underlying funda is simple - the lens mechanics detect the movement or the camera holder (the person who is using the camera) and compensates to a small extent for the movement/shake/vibration. Specifically, it compensates for pan and tilt of the camera. IS/VR features do not compensate for blur cause by the subject i.e. a fast moving car or a pouncing cheetah :)

So what's the big deal?
It is difficult for us to keep our hands absolutely steady while clicking a pic, especially when we are poised in unusual poses as we attempt to get that hatke angle. VR/IS is also useful when the lighting is not sufficient. It lets you slow the shutter speed by an additional 1 or 2 stops and yet achieve the same level of blur that you would have obtained in case of a non-IS/VR lens at a higher shutter speed. So you can slow down the shutter speed to 40 to let in more light and make the picture brighter, while still achieving the camera-holder induced blur-levels of a shutter speed of 60.

Should you pay the extra amount for a VR/IS lens?
I would suggest that you do. It's usually a small percentage over the price of the non-VR/IS lens but I personally believe that it's money rightly spent.