Originally posted by wolfiegirl
there's so much information already written, i always feel hesitant to ask. i figure if i have this question, someone else must have asked in the past too! and i don't want to clog up the forum with questions that have already been asked dozens of times. i've been on many forums where the keepers come storming out and go "search button is your friend". so i tend to do that and only start asking questions when i really get stumped.
thanks for the encouragement wiz. now to further your explanation... depth of field. there's a fine line isn't there between having the lens fully open and high speed and getting a decent depth of field?
Yeah the search function is a good way to start, but then again, repetition is good as it makes the lessons stick.
Depth of field is related to
a, the size of the sensor
b, the length of the lens
c, the area of the aperture
a, size of the sensor (or film stock) gives greater depth of field when it gets smaller (for reasons I cannot bring to mind at the moment.) Small sensors, such as are found in P&S camera give more depth to the 'in focus' field, which makes it easier to get everything in the pic in focus when doing party snap shots, etc. The larger the sensor the shallower the depth of field. so our APSC sensor gives a far narrower DOF than the P&S, but a full frame sensor will result in even finer DOF and then a medium format sensor would give even less DOF for a given focal lenght and aperture.
b, length of the lens. As someone said earlier, a wide angle lens gives less 'compression' to the image than a telephoto. So a pic taken with a 200mm F2.8 lens will have razor thin DOF compared to say the DA14 at the same aperture.
c, the narrower the aperture (higher number) the greater the DOF. This is to do with the rules of optical science, which is beyond my ken, and beyond what one actually needs to know to take a good photo, and beyond the scope of this answer. Just remeber, the bigger the F number, the bigger the 'in focus area.
So when used in conjuction, a fast, long lens on a large sensor will give razor thin DOF, but is a bugger to get in focus. A wide angle lens on a small sensor is a snap to focus because everything from near to the far distance appears sharp.
This is why P&S cams are great for happy snaps, not good for 'POP' (subject separation) or to get good bokeh.