I have always been puzzled by the multiplicity of numbers “Photographers” spew out when asked how they took a photo – “I took this pic at a exposure 1/30 sec and 5.6f using an ISO of 400” . Of course, as I can’t let my macho “Knows Photography” image suffer, I nod intelligently and change the topic :-).
When I have to take a difficult pic without flash indoors or at night (to capture the scene’s own lighting), I make a show of setting the manual mode on the Digicam, twiddling various knobs and buttons which change these numbers……….. and end up with an image that is shaken or is too dark 🙂
I got hold of a friend’s DSLR camera yesterday & decided to end my ignorance once and for all 🙂 I made a score of indoor shots of this vase with fake pink flowers among other things. Here’s what i learnt –
The pic on the right is shot in “Auto” mode. The camera fires off the flash because there’s not enough light in the room to get a good pic. The result is a bright image – but one in which the vase looks very “flattened”. This is because the scene is being blasted by a lot of light from quite close. The soft light and shadow areas that form in diffuse indoor lighting and create an effect of depth get lost. With the flash, sharp shadows of the object also fall on the wall if it’s close behind as in the pic above.
Getting a good indoor or night image without flash is relatively easy if you’re willing to lug around and whip out a tripod everytime you shoot pics. However, if you’re with a group, such behavior would usually be deemed extremely anti-social 🙂 Getting a good pic without getting booed for the tripod involves understanding & manipulating those Exposure, f number & ISO settings 🙂
Exposure is how long the camera allows light to fall on the digital camera’s sensor – usually expressed in fractions of a second. When there’s less light in the scene, the camera needs longer to collect enough light for a bright pic. However, the longer the exposure – the more likely it is that your hands will shake & blur the image. This phenomenon is largely statistical in nature apparantly & how “steady” you are with the camera has little bearing on it. Unless you have a good image stabilizer function in the camera or lens, odds are 50-50 that exposures longer than 1/30 of a second will have shake. Learn more about this here.
The f number indicates how large is the hole (aperture) through which light falls on the sensor. Larger apertures (represented paradoxically by smaller f numbers) let more light fall on the sensor. Aperture Size also determines something called depth of field – this is how much of the scene in front & behind your main subject is also in focus. This becomes very important if you are taking close up shots.
You may have guessed by now that in the Auto mode, the camera senses how much light is it getting from the scene and adjusts the f number & exposure time automatically for a satisfactorially bright & non-shaken image. It turns on the flash if it finds that the exposure time even with the largest aperture is too long to avoid your hands shaking. That’s why you end up with either shaken or too dark images if you turn off the flash manually and shoot.
The way around this is to play with the ISO setting. The ISO number defines how sensitive the sensor is to light – higher numbers mean more sensitive. The more sensitive the sensor, the faster it can collect enough light to get a satisfactory image. Normally, cameras shoot at ISO 200 or at most at 400. If you set a higher ISO, you can use a shorter exposure time.
Thus, I shot the left hand image in natural ambient light of the room – by pushing up ISO to the 1600 setting. This allowed me to use an exposure time of 1/10 of a second at the largest aperture – giving reasonable odds of getting a non-shaken image. I use the manual P mode which allows you to choose between different combinations of f numbers & exposure times. The higher ISOs however can also make a picture look somewhat grainy as in my pic above.
So that’s what you need to know about photographic mumbo-jumbo 🙂