Archive for the ‘Photo Tips’ Category

Digital Crop Factor

On Digital SLR’s, when mounted with a lens of given focal length, you would have noticed a considerable change in the Field Of View, when compared to a film camera. This is nothing but the “Crop Factor”.
Let’s consider the prime 50mm lens:

When mounted on a 35mm film camera the focal length of the lens remains the same i.e. 50mm, as the lenses are designed for 35mm films/equivalent sensors.

When mounted on any Digital SLR the focal length remains the same but due to the crop factor the field of view drops considerably, as the sensor sizes of most of the mid-level D-SLR’s are smaller than 35mm.

For Canon EOS 350D the sensor size is 22.2 x 14.8 mm

For Nikon D70S the sensor size is 23.7 x 15.6 mm

So a wide angle lens loses it’s field of view when mounted on a D-SLR (of sensor size less than 35mm)

For instance when a 50mm lens is mounted on a CANON EOS 350D D-SLR, whose sensor size is 22.2 x 14.8mm, the crop factor calculates to
crop factor = 35/(sensor size)

i.e. crop = 35/22.2 = 1.6
so now the field of view, for a 50mm lens, on a D-SLR translates to:

field of view = focal length of the lens X crop factor

i.e. field of view f = 50 x 1.6 = 80mm (i.e field of view is equivalent to a 80mm lens)

wow!! it’s almost become a tele photo lens. Note that the focal length remains the same but the field of view of this lens now becomes the equivalent field of view of a 80mm lens.

If you are a D-SLR (serious amateur level) user and if you are going to buy a lens then don’t forget the crop factor otherwise you end up picking up a 16-35 L series lens for 1,500 USD and when you mount it on your D-SLR you’ll have a field of view equivalent of a 25-56mm lens. So plan your buy keeping the full frame sensor in your mind.

Invest in expensive lenses only if you are going to switch to a full frame sensor in the future.

For Nikon and Fuji D-SLR users the crop factor is approx: 1.5

For Canon D-SLR users the crop factor is approx: 1.6

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Anatomical 18% gray card

Any SLR user (advanced) who shoots in “M” mode must have surely come across the term “18% gray”. So what exactly is this 18% gray and how does it affect exposure?

Mostly all cameras have an in-built light meter, which are calibrated for 18% gray i.e. the reference point for a camera’s light-meter to determine exposure are the surfaces that reflect 18% of the light that if falling on them. It is similar to a thermometer: At room temperature the thermometer stay at 94-97 deg i.e. the mercury in the thermometer remains stable during these temperatures. As the temperatures rise above this point the mercury starts reacting and shoots up the meter depending on the temperature it has been subjected to. So a reference point for a thermometer are the points at which it stays stable. Depending on this you can say if a person has a fever or if there is a drop in temperature. Similarly a camera”s light-meter is calibrated for, surfaces that reflect 18% light, or in other words, surfaces with 18% reflectance. So the mid-tones in your frame are rendered as surfaces that reflect 18% gray and deflection from this point results in an over or an under-exposed picture.

For instance if you compose a picture with your SLR camera in such a way that the frame is filled with any black material, the famous example is when you shoot a black cat. Place a black cat on a leather couch which is also black in color and then compose and shoot the picture with the whole frame filled with the black cat and the background, the black couch.

The results will be surprising you will see that the camera will fail to understand the shades of black and your picture will have a noticeable layer of gray on it. This is because of the camera calibration to 18%gray. Since the light-meter cannot find any mid-tones it renders the whole picture as gray. Similarly you can try this with your frame filled with only whites and you’ll see that the results are more or less the same.

So, how do we expose correctly for black cats ūüôā or rather when your frame is filled with same colors? The answer is very simple: “Use an 18% gray card/surface to determine the exposure”.

How do I take the reading for a good exposure? You can place the 18% gray card next to the subject of interest. Zoom in with your lens (or go closer) and now focus the gray card, adjust your shutter speed such that the light meter indicates perfect exposure. Now remove the gray card, zoom out and recompose your frame with your cat or whatever it is, DO NOT CHANGE YOUR EXPOSURE SETTINGS (let the reading be the one that you took off from the gray card) and then shoot et voila you now have a better and most realistic colors and shades of the picture as opposed to the one that the stupid light-meter has decided for you.

So now where do I get a gray card?

You can pick them at any of your local store for a few dollars.

What If I don’t have one or If you forgot one at home?

Most of the camera bag manufacturers (LowePro) provide the adjustable partition strips inside the bags with gray color. you can just strip on these and use it as your gray card. Alternatively an average human palm is supposed to reflect 18% gray so you are never out of options.

Tricky situations can be encountered when you are shooting a landscape with hills, clouds, flowing water, rocks and the green valley. Obviously, one cannot walk up to the hill place your gray card, come back place it on the water and then on the greens, take readings and shoot. The solution for this is quite simple and also complex

keep reading this blog for more on exposure techniques.

Good day people!

Avoiding Camera Shake

If you are an ardent shooter using a SLR (Single Lens Reflex) camera then am sure you would have experienced some shots with camera shake, even though it’s not dark. You would experience this quite often if you shooting in “M” (manual) mode.

Well there is a reason behind this and this is often referred to as the “Camera Shake rule

The safest shutter speed you can shoot without a camera shake is when you have shutter speeds greater than one over the focal length i.e. 1/f, where f is the focal length in mm, of the lens in use.

e.g. If you are engaging a prime lens like 50mm then for shake free shots make sure you shoot with shutter speeds greater than 1/60 seconds.

As the shutter speeds get slower the probability of loosing sharpness increases greatly.

Not enough light? use a tripod (with a shutter release), engage the flash depending on the distance between the camera (you) and the subject or brace the camera against any solid object. If you are not carrying a tripod then try to place your camera on solid base like a railing or any slab of stone near you alternatively you can try leaning on to a wall, take a deep breath and release the shutter without shaking the camera.

IF you have stable hands and follow the “photographer’s stance” with discipline then you can manage some sharp shots even at slower shutter speeds.

Hope this helps.

Good day and happy clicking

What is HDR?

I was introduced to HDR a few months ago through another flickr member.
The first thing you’ll notice in a HDR image is that the light is evenly distributed and the tones are more pronunced than a picture exposed using normal digital techniques.

Basically it means when you employ this technique you can produce images with a very high dynamic range for exposures in other words when you expose your picture most of us usually follow the light meter inside our cameras and some of us use external light meters: based on these readings we expose this picture but we will never have an exposure which is technically perfect i.e. we cannot have all the shadows exposed in a way so that every detail in the dark area is visible and at the same time expose all the highlights to avoid burn outs. Basically, it is difficult to acheive this dynamic exposure range using film, slide or digital techniques. HDR helps you to acheive that thus allowing you to create some nice and surreal images.

I hope you guys understood what I wrote up there anyways here is the definition

Definition:
In computer graphics and cinematography, high dynamic range imaging (HDRI) is a set of techniques that allow a far greater dynamic range of exposures than normal digital imaging techniques. The intention of HDRI is to accurately represent the wide range of intensity levels found in real scenes ranging from direct sunlight to the deepest shadows.”

You can wiki this for more information.

all right since we now know what HDR means so how do I generate one?

How do I generate a HDR Image

Things you need to generate a HDR image
1.Most importantly your image(s) itself.
You would require an image that has been bracketed for +/-1EV(Exposure Value) i.e. basically you shoot the same picture with different exposure settings, one slightly overexposed(1 stop), one slightly underexposed(1 stop) and one with exact exposure settings as suggested by your camera.
2.A software that can generate a HDR
PhotoMatix Pro is a popular one (HDR, Tone Mapping)
You can also acheive HDR using Adobe Photoshop CS2

Example:
Original Image

Stupas and Clouds - Original
HDR Image

Stupas and Clouds - HDR

Original Image

Cars Bangkok - Original

HDR Image

Cars, Bangkok - HDR

Some interesting links
http://www.luminous-landscape.com/tutorials/hdr.shtml
http://www.cybergrain.com/archives/2005/05/photoshop_hdr_i_1.html
http://www.hdrsoft.com/examples.html

What is Sunny 16 rule?

Damn!! I forgot that light meter..does that sound familiar.
A beautiful landscape is waiting in front of you to be clicked and you are left with your imagination on how to expose that frame.
Well..sunny 16 rule comes handy.

What is Sunny 16 Rule?

On a brightest sunny day the exposure is roughly equal to the reciprocal of your film speed or ISO setting (in case of digital slr) at f/16.

i.e. your shutter speed = (approx) film speed

so if you are loaded with a 100 ISO film then set your shutter speed to 125
and if you are loaded with a 200 ISO then your shutter speed would be 250 basically anything close to the ISO numbers.

Well, now what if it is not exactly that sunny.
Hmm..not to worry we can tweak this rule a bit to work for us.

If it’s slightly overcast then we need more light to expose so we open it up one stop (I mean the aperture) keeping the shutter speeds same as above.
so for 100 ISO film it would be shutter speed = 125 and aperture f/11.

If it’s slightly more than overcast then we shall open it up a little more..2 stops.
so we get for 100 ISO film, shutter speed = 125 and aperture f/8.0

and for the rest of the ISO’s you do the math.

Happy Clickin.