Apaature and shutter speeds

I understand, I think that the lower the F number the better. And it looks
like the average digital camera is an f2.8.

So, my question is, where does shutter speed come into play? And what is
shutter lag and all that other jargon?

What would I want in a digital P&S that is quick to take pictures (of kids
and sports) without getting blurry pictures? Also want it ultra compact ...
maybe compact.

 

Better for what?

A smaller f-number indicates a larger apperture, meaning that the lens can
let more light through; a large apperture also means that there is less
"depth of field" so you need more accurate focussing. In practice,
compact digital cameras usually have such a small image sensor that there
will always be considerable depth of field, meaning that more of the image
will be "in focus".

Most of the time, your camera will probably be using a smaller apperture
than the maximum it has available.

If you have a "zoom" lens, the maximum apperture available will get
smaller (= higher f-number) as you "zoom in".

Fairly typical and reasonable for a compact camera.

A higher shutter speed (= faster shutter, shorter exposure) will let light
through for a shorter amount of time. High shutter speed is good for
avoiding "camera shake" (where the camera moves while the shutter is open)
and for reducing blur if the subject is moving. A longer exposure is
useful for getting a picture if there isn't much light - provided the
subject isn't moving and the camera is perfectly still.

The time you have to wait between pressing the button and the camera
actually taking the picture. This is often a significant problem with
compact digital cameras, making them difficult or impossible to use for
"action" shots.

There are books full of answers to that question )

Kids: look for cameras with "image stabilisation" and good flash. Things
like "face recognition" and "portrait mode" might be worth having.

Sport: image stabilisation is useful here too - and you *must* be able to
turn the flash off so as not to disturb the other spectators or the people
taking part (you might be thrown out of the event for using flash, in some
places). An eye-level optical viewfinder can be a godsend for any outdoor
photography, but few compact digital cameras have them these days - and
the LCD 'screen' is not always going to be useable in daylight, no matter
what the advertising claims.

Don't expect any digital compact or ultra-compact to be particularly good
for sport photography; but they can be very effective for family-album
snapshots. Get to know the camera well before you try using it for
anything important.

 

Smaller F number better for portrait pictures, to make the background
slightly softer and the person more in focus, also reducing the depth of
field... correct?

And getting a camera with a fast shutter speed will be better so my pictures
won't be as much as a blur when my kids are moving around? That and one with
IS. 1/2000s decent or are the better in a P&S?

What can you or anyone else tell me about the Nikon S510, P50, P5000 or the
Canon A720 IS... those are what I have been looking into, but can't seem to
figure out which one will be the best for me.

Pictures of:
Kids, kids playing sports, every day activities.
I do want at least an 8 MP, I do on occasion make my pictures bigger than the
regular 8x10.
Movie mode - I love using it now.

They have one that is a S51, but it's a f3.3 which someone told me wasn't
good, and that I wanted one that was at least as low as a f2.8 - which is why
I asked. But I like that the others have better optical zoom, not much, but
still, more, and I know the Canon has a lot more, but just not sure about it.

 

You won't get very much of an effect like that with a point-and-shoot
compact digital camera; the image sensor is too small. Simple 'auto-focus'
and 'auto-exposure' makes it something you can't easily control anyway.
But some cameras have a 'special effect' to artificially blur most of the
background in 'portrait mode' - and of course, image processing software
can do that (takes practice!).

You an only use a fast shutter speed if there is enough light. Most
digicams let you change the sensitivity of the image detector (higher ISO
number = greater sensitivity which makes a higher shutter speed possible)
but there is a trade off in image quality with greater sensitivity.

I doubt if you'd notice any difference in practice between point-and-shoot
cameras with maximum appertures of f/3.3 and f/2.8. Other factors, such
as the image sensor used, the quality of the lens, and the design of the
electronics and software inside the camera, are more important.

Try looking at <http://www.steves-digicams.com/> and
<http://www.dpreview.com/> for information and reviews of particular
cameras.

 

Correct with larger cameras, but very small cameras have so much depth of
field you usually won't be able to reduce it much.

Image stabilization is always good to have. I wouldn't worry too much about
shutter speed in a small camera. You would seldom if ever need 1/2000 in
such a camera and might not be able to use it anyway unless the light was
very bright. Higher shutter speeds = less light passing through the lens,
and you need a certain amount of light to get a good picture.

The S510 is very flat and pocketable, if that's important to you. It has a
nice large LCD monitor but no optical viewfinder, which may or may not be
important to you. Personally I find *all* LCD screens hard to read in bright
sunlight and for that reason prefer a camera which also has an optical
viewfinder. But apparently some people don't mind the absence of a
viewfinder.

The P50, P5000 and P5100 have optical viewfinders as well as a large LCD
monitor. I like them better for that reason, and also the fact that they
have more user controls and should be more capable cameras generally. The
P50 also has better wide angle capability than the others mentioned, and
should be attractively priced. But it doesn't have real optical image
stabilization -- it has *electronic* stabilization which is not as
effective.

The P5000/P5100 are the most advanced Coolpix models available today and
priced accordingly. They both have real optical stabilization which is good.
If you're a beginner they probably have more features than you need -- you
may or may not "grow into" such a camera.

Not necessarily. In ordinary use you probably would not notice the
difference between a camera with f/3.3 and one with f/2.8, and also keep in
mind that these f-numbers only apply to the lens at the *short* end of the
zoom range -- at the long end, the f-number is invariably higher ( = smaller
relative aperture) in this type of camera, and the long end is where you'd
really prefer to have a larger aperture. Many compact/ultracompact cameras
are f/5 or so at the long end.

A longer zoom is nice dependng on circumstances, but may not be very useful
if the aperture at the long end is very small, since the longer the zoom the
more it magnifies camera shake -- so to avoid blurring the picture you will
need a higher shutter speed, and if the aperture is small there may not be
enough light for the camera to set a higher shutter speed. Generally
speaking, if you need a pocketable camera I would advise not being too
ambitious about zoom ratio. If you really want a camera with a long zoom
range I'd suggest looking into one of the several "superzoom" models on the
market -- but none of them are really pocketable. So that's the trade-off.

Neil