What is the meaning of macro and digital zoom in photography?
Macro photography: It refers to close-up photography; the classical definition that the image projected on the "film plane" (i.e film or a digital sensor) is close to the same size as the subject. On 35 mm film (for example), the lens is typically optimized to focus sharply on a small area approaching the size of the film frame. Most 35mm format macro lenses achieve at least 1:2, that is to say, the image on the film is 1/2 the size of the object being photographed. Many 35mm macro lenses are 1:1, meaning the image on the film is the same size as the object being photographed. Another important distinction is that lenses designed for macro are usually at their sharpest at macro focus distances and are not quite as sharp at other focus distances. In recent years, the term macro has been used in marketing material to mean being able to focus on a subject close enough so that when a regular 4×6 inch (102×152 mm) print is made, the image is life-size or larger. This requires a magnification ratio of only approximately 1:4, more easily attainable by lens makers. Digital zoom: Digital zoom is a method of decreasing (narrowing) the apparent angle of view of a digital photographic or video image. Digital zoom is accomplished by cropping an image down to a centered area with the same aspect ratio as the original, and usually also interpolating the result back up to the pixel dimensions of the original. It is accomplished electronically, without any adjustment of the camera's optics, and no optical resolution is gained in the process. Because interpolation disturbs the original pixel layout of the image, as captured by the camera's image sensor, it is usually considered detrimental to image quality. The results of digital zoom are, however, sometimes superior to the results of manual cropping and resizing (interpolation) in post-production. This is because the camera may apply its interpolation before performing lossy image compression, thereby preserving small details that would otherwise be lost. For cameras that save images in a raw format, however, resizing in post-production will yield results equal or superior to digital zoom.
Photographers, for practical purposes how much better is 30mp than 20?
One is about 6000x5000 the other is about 5000x4000. In the grand scheme of things that may give you about 1.2 x 1.2 pixels instead of 1 pixel in the same space so there may be marginally better resolution, but that will depend on the lens, shooting conditions, etc, etc. For the same size sensor, the pixels will be smaller so the light gathering properties will be marginally less and higher ISO behaviour may be a little worse. Really, unless you are going to be printing/displaying at full size you are probably not going to see a whole lot of difference. Update What are you intending to photograph? The top of the range Nikon D5 is 20.8 MP. The top of the range Canon 1Dx ii is 20.2MP. Pixels aren't everything.
Photography questions about bracketing?
Movement blur from the subject or from camera shake is the only problem you will really get from bracketing with the shutter speed. There are actually numerous reasons to bracket shots, not just for HDR. Camera meters may well have become more accurate but they still do not necessarily meter a scene correctly for the image. Most still using centre weighted metering which can cause problems in itself.
Photography in a low lit room?
Tough situation. You do the best you can and hope that your camera is up to task. The smaller sensor on the Olympus might be problematic. I have several "low light" images on Flickr and there are some on the first page that seem to match your situation - meetings in dark rooms. Some are actually with the lights out. Click on the thumbnails that looks appropriate and see what settings I used. http://www.flickr.com/photos/samfeinstei... The real answer for you is probably get a fast prime lens, like f/1.4 or f/2.0. I don't know the Olympus line, or I'd be more specific. You might be able to use a tripod to allow longer shutter times also. Most of the time, people at meetings are not so animated that you can't get away with 1/15-ish shutter speeds. Some of mine were taken by sitting the camera on a table top and using live view, because I did not have a tripod with me. If you don't have live view, you can experiment and keep checking the LCD to see how you mayhave to re-aim your camera before trying again.