basic lens mechanics

I searched the forums for an explanation of basic lens mechanics but was unable to find any links. Any one who needs some practice or has time, could you please explain the basics of lens mechanics or where I can go learn some.
E.g., things like: what is the relationship between focal lengths and choosing a lens. I just feel like I have a weak grasp of understanding of lenses and when to choose a lens to use and how.
THanks

Hmm... there's probably something on www.howstuffworks.com or similar sites but I don't have any links.. try just googling some information?

If you want my definitions, though... 50mm is approximately a "normal" lens which will give you an image which is roughly in perspective with what you see normally. 100mm+ is starting to zoom a fair bit and compress the image so that the subject will appear closer to the background... 35mm and wider (or is it 24mm and wider?) is wide-angle and will exaggerate perspective and give you a wider angle of view, used for landscapes and distorting stuff.


Non-zoom lenses (primes) generally have better colour, contrast and sharpness than zoom lenses (at least in my experience!).

A f/2.8 lens will let in twice as much light as a f/4 lens and is therefore of more use in low-light situations where you might get motion blur from the subjects moving about... by the same token a f/2 lens lets in twice as much as a f/2.8 (and four times as much as a f/4) so could get a shutter speed twice as fast again. Look up the f/stop on google and in the forums and you'll find oodles of explanations, keep reading until you find one that makes sense to you Also try looking up the law of reciprocity to do with photography.

Hmm, well that's a little bit of stuff from a non-expert, hope it might help.

Jim

What camera are you using or intending to own? Each different format (size of film or digital sensor) dictates a different "normal" lens focal length. A Digital Rebel, Rebel XT, 20D, and 10D all use a digital sensor with a size known as APS-C. They all use about a 31mm focal length as a "normal" lens. A 35mm film camera or a full-frame digital camera uses a 50mm lens as a "normal" lens. Lenses shorter than "normal" is considered wide-angle, and lenses longer than "normal" are considered telephoto.

There are two basic types of lenses. One is the "prime" lens, or one with a fixed focal length. The other is a zoom lens - one which can be adjusted to a range of focal lengths.

All modern lenses have an adjustable iris (like the iris in your eye) that can change the amount of light that enters the camera body to make an image. With a larger opening, more light gets to the film/sensor. The opening is usually defined as a ratio, using f-stop numbers. The standard numbers are f/1.4, f/2.0, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, and f/32. The smaller numbers relate to wider openings and are called "faster" because you can use a faster shutter speed with the wider opening. The higher numbers are called "slower".

Longer focal lengths (telephoto) can be used to take a photo of something far away, as if you are using a telescope. Shorter focal lengths can be used to take a photo of a wider subject without moving back (or if you can't move further back). This is the first thing that most folks think about when trying to choose a lens. However, there's an even more important (to the creative photographer) reason to choose different focal lengths for an image. Here's a link to another thread in these forums where I described this to a few folks and there are some examples there too: https://photography-on-the.net/forum/showthre​ad.php?t=94147

Hope all this makes sense and gets you a little closer to understanding what you asked about.

Lens mechanics sounds like you wish to know how lenses are put together for that I recommend the Canon Camera Museum

http://www.canon.com/c​amera-museum/index.html

For what you described it is fairly simple
If the focal length number is smaller then the lens has a wider field of view (or regard) thus you can see more area in the lens. If the lens has a higher number (AKA a telephoto) then you can see less field of view in the lens.

Related to this is distortion and flatness, the wider the lens (smaller number) the more distortion that will be present in the perspective, the longer the lens the more flat a particular subject will appear.

For 35mm cameras a 50mm lens is considered normal the distortion is similiar to what our eyes percieve (not necessarily same field of view) so anything with smaller number is a "Wide" lens anything bigger is a "long" lens.

Now on to their uses.
Wide lenses work best for landscape views so you get that grand view of the landscape.
Normal to slightly telephoto lenses tend to work best for portraits.

Long lenses tend to be used for sports and wildlife as you usually can't get close to the action so they bring your view closer into the subject.

For photojournalism and street life a normal to wide lens seems to be a good choice for general use.

And everything else depends on what it is.

The other primary characteristic of a lens which is aperture affects how much light the lens can send through to the sensor, but it also affects depth of field the wider (or more open or smaller number) the more light through and the shorter the Depth of field or in-focus area will be. For some shots you want a deep depth of field for others you want a shallow depth of field. A shallow DoF isolates the subject, A deep DoF brings the subject into the background.

Lastly Zooms and Primes. Zooms give you a range of focal lengths to use, but primes can be designed to have higher quality and a larger aperture (smaller number) (most zooms are really good on the quality aspect these days). Primes also tend to be lower cost for the quality level of the imagery they provide.

The best thing I recommend is get a 50/1.8 or 50/1.4 and see if you need a wider lens (such as 24mm) or a longer lens (such as 85 or 200mm to get what you want and that will let you decide what you need for focal length. Also pay attention to the aperture you use the most so you know if you need to spend on the more expensive lenses or not.

Hope that helped a little bit.

Just a small point- so that you don't carry around missunderstandings for the rest of your life as there is alot of missinformation on this subject if you search the net-
As stated above by others, for most digital bodies a 28mm or 35mm lens is considered normal.
On the internet you'll find a great many definitions on what a 'normal' lens actually is ,but only one makes any sense at all...a normal lens will give similar magnification to the human eye.
It has nothing at all to do with field of view or depth of field,etc.
(also don't try to measure this by looking through the camera because the viewfinder has it's own magnification factor that will confuse the issue)