Topic: Buying a Camera

[Muffin]

Heh, now you can start taking 3D pictures. 
I'm preparing my googles.

[Muffin]

Aperture and shutter speed
A Tedious Explanation of the f/stop
A Tedious Explanation of Depth of Field
 - check out these excellent and easy to follow articles on apertures, depth of field, shutter speeds. I will only write a short summary of the very basic concepts, taking inspiration from these, and explain how to read the specifications for these.

Shutter speed is easy - it is how long the shutter is open and lets light on the sensor. The only thing influenced by this is exposure and blurriness of the image. Longer shutter speeds will pick up more movement. Most of the time this is annoying, other times it's good. Starting from 1/30 seconds cameras will pick up the micromovements caused by your breathing, and if you think that if you stop breathing helps, then think again. Your heart still beats, and the blood is being pumped to and from your fingers - which will move the camera. Some lenses have built-in vibration reduction, Canon calls it IS - image stabilizer, Nikon calls it VR - vibration reduction. Look for these letters in the names of the cameras and lenses, but even better if you read the specifications. Canon dropped these letters from the official model names, since all of their comapct cameras now have IS. Check if you're in doubt.
  Even with IS/VR it is almost impossible to have sharp pictures with exposures above 1/10 - that's a tenth of a second. If you need even longer exposures then think - tripods; or be creative, find something to put your camera on .

Shutter speed is expressed in second and fractions of seconds. Like this:

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8 seconds    4 seconds    2 seconds    1 second    1/2 second    1/4    1/8    1/15    1/30    1/60    1/125    1/250    1/500    1/1000Camera manufacturers will usually specify the shortest value, since that the most significant. Keeping the shutter open for one second is easy. Keeping it open for 1/4000th of a second requires precision work and high quality durable materials.
Canon S95 has a 1-1/1600 shutter speed, I'm not excited about the 1" upper limit, but it's still a good range for most anything.

Long shutter speed - the bad



Long shutter speed - the good


Long shutter speed - the questionable

I forgot that I was on longs exposure mode


Aperture is how big the opening is in front of the lens. Together with the shutter speed is the other determining factor for exposure.
Lenses/cameras with large aperture are commonly called fast lenses, because they allow you to use faster shutter speeds.

For sake of convenience, the aperture is given by the ratio between the diameter of the hole and the focal length of the lens. It is expressed in f/stops from from f/1.4 to f/22, where the standard scale is:

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1.4    2.0    2.8    4    5.6    8    11    16    22 Smaller values represent larger apertures!
Just like with the shutter speeds, each of these values halves/doubles the amount of light that enters onto the sensor - the whole is a circle, the value designates the ratio between diameter and focal length of the lens, and with each step the area of the circle is doubled or halved. Take a 50mm lens and do the math if you don't believe me.
Thanks to the f/stop being a ratio between size and focal length, f/stops represent the same amount of exposure
regardless of the focal length of the lens used. An f/2 aperture on a 26mm lens will provide the same amount of light then a f/2 aperture on a 50mm lens, though the actual physical size of the opening will be different.


As you can see both the scale of apertures and shutter speeds is a halving scale, which means that you can achieve the same exposure with different set of values. Say that you decide that 1/125th at f/8 gives you the correct exposure, then all of the following values will give the same exposure:

Shutter Speed	1/4	1/8	1/15	1/30	1/60	1/125	1/250	1/500	1/1000	1/2000	1/4000
f/stop	f/45	f/32	f/22	f/16	f/11	f/8	f/5.6	f/4	f/2.8	f/2	f/1.4

Which one you will use will depend on the effect you want to achieve.
The aperture is one of the biggest factors for the depth of field of an image - along with focal length and sensor size. Depth of field is simply the distance before and behind the subject that is in focus - how many "stuff" is in focus in your picture.
Large apertures (lower f/stops) produce a smaller depth of field, and are great for portrait photos and other creative work. Smaller apertures give a very large depth of field which makes them preferable when shooting landscapes and architecture. You can see lots of examples that illustrate the depth of field concept in my galleries.
Shorter shutter speeds are good at "freezing" the moment, so they are frequently used for sports and action shots, or capturing anything that moves. Snapping a swan in it's flight and have his wings sharp requires extremely short shutter speed, large aperture and good focusing.

How to read the specifications:
If you recall, aperture is a ratio between size and focal length. This means that on zoom lenses to have the aperture f/2 on the whole range of focal lengths, the radius of the opening would have to grow and shrink as you zoom in/out. This is a difficult engineering task - lenses are already made up of complex individual elements, designing dynamic shutter apertures complicates things even more. Therefore lenses that maintain aperture on different zoom levels are few and far between and extremely expensive. Over the $2000 mark.
Manufacturers will always specify the values at the low end and the far end of the focal length. Like this:

Canon S95	CoolPix S8100 Black

For Canon you can see the maximum and minimum apertures at the two extremes (Wide - 28mm, Tele - 105mm).
Nikon says only the maximum apertures, so f/3.5-5.6 means an f/3.5 aperture at 30mm and f/5.6mm on 300mm.
In terms of "speed" Canon wins on the wide angle, but Nikon has an edge on the far range - with it's larger zoom factor. At the far end both cameras are pretty much the same, but Nikon "sees" further.
If you plan to shoot lot's of portrait photos or close-up, in low light (or not) conditions the Canon is a better choice. If you need zoom to see far in normal light conditions the Nikon is better.
Keep in mind that I didn't bother to take two same-range cameras for comparison, you might find a faster Nikon camera with the same good zoom. Or a Cannon with a better zoom range. Apples and oranges.

I have a 50mm f/1.4 lens. One of the fastest lenses ever built. It is expensive. I didn't pay extra money for a fast lens and not use it to it's fullest potential. I shoot almost always at f/1.4, sometimes I stop down to f/2.0 or f/2.8.

Depth of field - the bad



Depth of field - the almost good


Depth of field - the good


Depth of field - the star

Thanks to the creative use of the depth of field, it is obvious who's the star in the picture above.

[Michael]

Thanks for that Rudi - it is very interesting as I have been looking at compacts recently. Having just blown my bank account on a car, I will wait till mid year to upgrade my camera. But I'll take all this into account.

I recently talked with Ben (on top of the mountain) about his compact. He said it wasn't a reflex, as they are more expensive, but had a very long zoom. It was a Panasonic. But he also said it didn't take RAW, only JPG.

I found looking at the back screen to take the picture, not very useful. And obviously only being able to output in JPG was compression from the word go. A Photoshop expert once told me, every time you save as JPG, it loses quality. It doesn't just save at the same quality as it opens with, even on 12.