How does ASA setting affect a digital photograph? I know w/ 'old school' (aka film/slide) photography, the higher the ASA, the more f-stop you could get at a similiar shutter speed, and hence more depth of field. Or, you could get a faster shutter speed at the same f-stop But, that came w/ a price - film graininess increased w/ higher ASA's. So how does a higher ASA impact digital photography? I would assume since there is no film, the image doesn't get grainier (at least it doesn't seem like it does w/ my experimenting). What are the downsides to increasing ASA? Should we always use the maximum ASA settings for model photography?
The difference is "resolution". If you take a high resolution photo the pic can be blown up to a very large size. If you take a low resolution pic, it will show the pixels (doppled) when you try and enlarge it. In that sense, there is really no differance between digital and film: a low ISO rating = highter resolution .. higher ISO ratings = corresponding loss of resolution.
Tha ASA/ISO rating of a film is a measure of the film's speed. The higher the number the faster, or more sensative to light, the film. Thus with a fast film you can do more with less light. The problem is that the faster films have larger grain size, which limits how big an enlargement you can make. When I worked for a newspaper, a film with the speed of 400, or more was good because we were not as concerned with grain. A portrait photographer, on the other hand, would want the finest possible grain and use a film with the speed of 100 or less. This is true with both black-and-white and color films. The makers of digital cameras have tried to emulate the various film speeds and use the same ISO numbering system. Interestingly enough, similar problems exist with both film and digital. The higher the sensitivity (higher ASA/ISO), the more grain, or in digital terms, more noise. This does translate into resolution. The fine-grain films have better resolution because the smaller the grain, the sharper an image can be. In digital terms, the less noise, the better. Generally, I keep my digital camera set at an ISO setting of 100, but I go to higher settings if lighting conditions demand it.
