The camera’s sensitivity to light
There are 3 basic things that affect the overall quality of the image that you photograph in a modern-day camera. They are ISO, aperture & shutter speed. These 3 depend highly on one factor which is light. What makes a photograph really is a chemical process when light is exposed to film or the sensor in a digital camera.
While the aperture & shutter speed generally control the amount of light which hits the sensor in a digital camera, ISO is somewhat different in the sense that it controls the sensitivity of the sensor rather than the light that comes in to the camera. The sensor is more sensitive to light as the ISO increases. Typically the ISO starts at 100 for most digital cameras & progress to about 3200… or where the 5Dmk2 is concerned, 6400. So the sensitivity of the sensor increases as the ISO increases in relation. You would need less light to create a properly exposed image when you dial the camera to ISO6400. However there is a catch, if you keep shooting at ISO6400 all the time, you will notice noise or grain on your images. So in relation to aperture & shutter speed, photography really is about controlling light & minimizing noise on your output image by limiting the use of high ISO. This is why light is so important to photography, without it there simply would be no photography. In fact without it there would simply be no sight!
Controlling noise & using the appropriate ISO is vital to creating clean images. If you are using film, what you get is graininess images… in some cases graininess adds mood to your photos & at times actually makes a photo looks good. However digital ISO noise is undesirable & appears as if blotches of colored blobs on your images.
Why are some cameras better at handling high ISO than others?
The larger the camera sensor size, the lesser the noise generated on high ISO. This is why consumer point & shoot cameras can’t shoot higher than ISO400 with good results. This is also the reason why full frame DSLRs do better at handling noise compared to their cropped sensor counterparts.
What is also interesting is that, with higher megapixel, noise levels at low ISO is even lesser. ISO100 on the 5Dmk2 is silky smooth. On the other hand, with lower megapixel, noise levels at high ISO is better controlled. So technically a D700 at ISO6400 will produce more controlled noise levels than the 5Dmk2 at the same ISO level. Something to know, but not necessarily get hung up about when making your choice of brands if you are in the market of purchasing either. The differences between these 2 cameras are almost negligible in terms of image quality. If you need to decide, get the camera that doesn’t get in the way of you getting the shot.
Even if you are using a low-end DSLR, doesn’t mean you can’t shoot high ISO. The shot on the right was taken at ISO3200 on a Nikon D60 at the Lion King show in Hong Kong Disneyland. Folks who use or have used a D60 know exactly what I mean when I say this camera has very limited capabilities producing good quality images at high ISO… & yet I managed to get this shot.
When is the right time to boost up ISO?
There are some questions that you will need to ask yourself before you make this decision…
Are you using a flash? You don’t need to turn up your ISO too much if you are using a flash to aid with your photography.
Are you using a tripod? Using a tripod can reduce the need to bump up ISO. Using a VR/IS lens will also reduce the need to turn up ISO.
Are your subjects moving? If you wish to freeze your moving subjects, then you will need to turn up ISO.
Do you need a large depth of field? Sometimes even in broad daylight I find myself dialing up ISO simply because I needed a large DOF to get the shot that I’ve envisioned.
Can you get away with grain? Are you enlarging the final image? Are you posting on the website or printing.
All the questions above is your check & balance to see if you really require higher ISO or not. Even though digital cameras these days have superior noise reduction capabilities, your knowledge in controlling noise levels at the source is far more important & effective than relying on your camera or any noise reduction software that is available on the market. The rudimentary key is to ensure that your images are at its cleanest right out from the camera with minimum image manipulation as possible.
Does this mean I should use a flash, tripod & make sure my subjects don’t move to avoid using high ISO??
Absolutely NOT! It all really depends on the final image that you are looking for. Using a flash in all your photos may not create the emotion that you wanted an image to portray. In fact the use of high ISO, a stopped down flash with a diffuser is preferred to gather enough ambient light in a room for instance for indoor photography. Too much light from the flash will create flat looking subjects which are also not desirable. If you haven’t already read my previous article, use a 50mm to enable you to shoot at lower ISO since the 50mm has a much larger than normal aperture of f/1.8. This extra stop or two can seriously make a difference when you are faced with low light situations & can’t or don’t wish to use a flash to take the shot.