Canon EOS Rebel Xs with EF-S 18-55mm f/3.5-5.6 IS lens.
All shots are in Manual Mode....karma


Photography

Physic: Light

Light travels in a Straight line.

How much light your lens sees or receives, not you, is what you get on your digital camera’s sensor. Therefore size of sensor measured in mega pixel also matters. Unfortunately, full frame, ie 35mmX 35mm size, cost too much unless you are making a living out of Photography.

How to control light: Dark or Bright

Other factors that influence lights passing through your lens are; Shutter speed (how fast you close the lens), Aperture (how big or small your lens opens); and ISO settings (how sensitive your digital sensors are to low lights).

By manipulating these three factors, you can control the amount of light passing through your lens and will make a difference to image quality- bright or dark.

If you want to control all these 3 factors, your camera must be in Manual Mode- M.

F-Stop: Aperture

Bigger Hole will let in more light and smaller hole will let in less light-physics. If you want more light to fall on camera’s main sensor because the subject is in the shade or subject itself is dark, open the hole as big as possible. Dark objects do not emit light but absorb lights…physics.

However, there is an optical problem if your Aperture hole is big or wide open.

Depth of field

If your lens hole is big (Aperture is wide: below image A has F-stop 1.8/iso 100/Shutter speed is 125/Flash/Indoor) whatever is in the front appears sharp but background(candle) goes out of focus.




However, if your lens hole is small (Aperture is small: below image B has F-stop 10/ISO 100/Shutter speed 125/Flash/indoor) both the subject and the background image(candle) comes into focus.




That is the side effect of Aperture control.

F-stop

Size of Aperture (how big or small it is open) is called F-stop, now a days. Higher the F-stop number is, smaller the hole or Aperture size becomes. That is the other “human” confusion added to Aperture puzzle.

Therefore F 1.8 has bigger hole to pass light through than F 10 in above images. If you want more light to pass through your lens, open a bigger hole or set the Aperture to smaller number but remember you are losing Depth of Field.

Dark objects, shades, inside rooms and nights are not emitting any light or your camera’s sensor will not pickup much needed light. Use Flash- build in or extra lights. Use reflector or white boards,white cloths or walls or white ceilings to reflect any light source on your subject or models.

Shutter Speed

Slower Shutter speed means lights are given more time to come in and fall on the camera lens. Therefore brighter the subject becomes. However human hands cannot hold camera still for more than 125 of a second-safety level is included here. If your subject needs slower Shutter speed than 125 you have to use Tripods- Heavier Tripods are better for stability in a windy or watery or beach shooting situation.

Higher numbers are faster Shutter speed, therefore less lights. For example 1000 is faster than 125 of a second Shutter speed. Flying Birds, sports or moving subjects require high Shutter speed to freeze the action or else image will blur.

ISO number

Image must be formed either on film (light/photon reacts with light sensitive chemicals) as in old days or on light sensitive devices such as CCD or CMOS (light/photon falls on these photon sensitive pixels which gets electric charge). Sensitivity to light is called ASA in old days and today it is called ISO in digital world. Unlike ASA which is fixed for a roll of film, ISO can be changed from subject to subject.

Higher number ISO means, it is more sensitive to light-same as getting more light through the lens. If ISO is pushed to very high, there is a side effect- noise. Noise is unwanted thing. Very high ISO can make your image blur.

Low ISO has the best quality or sharpness. However, if subject is dark even after controlling Shutter speed low, Aperture wide, then only alternative left is to push the ISO to higher number- How about using a Flash instead.

Wide angle

If you want to capture a wide scene(whole more of the landscape), you need smaller focal length lens- physics. For example 24mm is better for wide angel scene than 35mm lens (image/subject is formed at a distance of 35mm from where the lens is).

Movies are made in wide-angle. Some natural scenes are better in wide-angle too.

HDR: High Dynamic Range

This is a new buzz word. Here is a scenario.

Taka a look at picture A (I took this shot at somewhere in Cumberland, Toronto). If I make more light to come into my lens, it will show more detail in the dark hallway which has only few florescence lights to light the hallway. But I will miss the details in the far end of the door where sun is the brightest (around 12 noon which is lighting up the street).


Now look at picture B. If I make less light to come into my lens foreground detail is lost but I will gain more detail about the far end of the door and its surroundings.


There is no middle ground. Camera lens can deal with light that is either harsh or mild but not both at the same time.

Here is picture C. I opened both the pictures A and B and superimpose one over the other in Photoshop and walla. I have a mix of both—not very good one as I have moved from my original position and also people showed-up. Since my camera does not have HDR option (my camera and iphone both are getting old, including me) I had to use Photoshop to get the message across.




Modern cameras or high end cameras have HDR option. Whenever you think that your subject has a high contrast(lights and shade- noon is worst), you can select HDR mode from your camera menu system or page. What it does is, it will take two pictures at superfast speed similar to A and B ( one under exposed, other over exposed). Next, it will superimpose one over the other and create C without Photoshop. And camera will retain all the three pictures if you want to compose it in another way. That is the magic of HDR and digital world.

Colors/Art

Art of taking pictures depends on experience and knowledge. Both can be acquired.

Here is a link to light and lenses

http://graphics.stanford.edu/courses/cs178/applets/applets.html#lens



more photos at my Google Plus site