Lens talk

So what do all the numbers mean. How do I know what to look for.
ie. 18-55 means what?

18mm at the short end, 55mm at the long end.

Sorry, I'm really new, I still have no idea what that means to the person holding the camera/using the lens.

It's the focal length. I'm not an ubergeek so I can't really explain what it means exactly. I CAN tell you it's the "wideness" or "zoominess" of the lens. 18mm is kinda wide. 55mm is normal-ish (naked eye view sorta) and 200mm, for example, would be telephoto...for sports, etc. but not HUGE field sports...it's kinda short for those. Lemme try to put together some samples real quick to actually show you the differences.

https://photography-on-the.net/forum/showthre​ad.php?t=219574

check out the link provided by crn3371

Not the most exciting subject matter, but here you go. These were all taken on a tripod from the same exact location. Focal lengths (mms) are on the photos themselves.

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Nothing like a visual to explain things. Nicely done.

What the heck is that thing that plugs in on the table. It doesn't look like a lamp.

ssim wrote in post #2042728
Nothing like a visual to explain things. Nicely done.

What the heck is that thing that plugs in on the table. It doesn't look like a lamp.

Thanks Sheldon.


It's an ice cream shaver...to make your own Italian Ice.

wow, i must be dumb, I still have no idea...

PixelChick78 wrote in post #2046240
wow, i must be dumb, I still have no idea...

It is essentially the field of view. At 18mm the field of view is very wide, taking in a lot of the area in front of the camera. As you move toward 55 mm, you take in less of the veiw, but still fill the frame of the photograph (magnification). 18mm is considered very wide - 500mm is considered very long.

The photos above show you very explicitely the effect of increasing the focal length. I really don't know what else we can do to explain it to you.

Mark

ok, that helped. So, if I have this right, when you turn the dial on the lens from 18mm towards 70mm , in the viewfinder it will look like your zooming in as you get to the larger number on the lens?

Can you tell I have a point and shoot yet? LOL Thanks for being patient with the new girl

I want to understad what to look for when I go shopping.

Have a read of this,

http://en.wikipedia.or​g/wiki/Telephoto_lens

Pixel, I'm going to go ahead and explain this, forgive me if it is overexplained or underexplained.

I assume you want to know what a given lens means, when talking about a lens. I will briefly explain each part, and some extra specifics about canon lenses specifically.

Let's take a normal lens, in this case, you're referring to the EF-S 18-55mm f/3.5-5.6. I will break down each of those parts.

First, EF-S. This part of the lens name refers to the lens' manufacturer's designation for the mount.

The mount is where the lens attaches to your camera. Different cameras have different mounts, and camera/lens manufacturer's mounts change over the years. This is why you can't take an old old canon lens and attach it to your digital rebel today, without some sort of an adapter. The way the lens attaches to the camera body is different.

Popular canon mounts of today are listed as:

EF, which stands for "Electro-Focus". This is canon's term for their autofocus lenses. These lenses can be used on the new digital SLRs, as well as modern film cameras.

EF-S, which stands for "Electro-Focus - Short back focus". This is canon's term for the lens mounts specifically desgined for use with APS-C sized image sensors. Current canon dSLRs that are compatable with this type of lens include: 300d, 350d, 400d, 20d, (20d) 30d.

FD mounts were used before EF mounts, and FL mounts were used before those. Neither of these are mainstream lens mounts anymore.

18-55mm refers to the focal length of the lens.

To over-simplify, the focal length is the "zoom-in/zoom-out". The smaller the number, the more 'zoomed out' the lens. The larger the number, the more 'zoomed in' the lens. (mind you, this is oversimplifying focal length to a fault, but it may help with a basic understanding.)

When talking about a lens that only has one focal length, we call that a prime lens. That means you cannot zoom in or out, except by using your feet to walk closer to the subject. The rules above remain the same.

When talking about a zoom lens, like the 18-55mm, it tells you the range it can zoom from. In this case, it can zoom OUT as far as "18mm" and zoom IN as far as "55mm".

Now, lets take a closer look at focal length, without going into all of the complicated factors that involve focal length. Focal length is a measured distance from a lens and a focal point. In this case, your image sensor or film. For some nice illustrations of this, feel free to visit http://www.cambridgein​colour.com/tutorials/c​amera-lenses.htm

The longer the focal length, the narrower your field of view becomes. I just thought of a neat way to experience this. Get a string or a rubber band. Make it about 2 feet long, and tie it so its a circle. Then set it up in your hands like this:

Left hand String Right hand
||-----\ /-----||
|| \-----\ /-----/ ||
|| \-----\ /-----/ ||
|| \-----\ /-----/ ||
|| \/ ||
|| /\ ||
|| /-----/ \-----\ ||
|| /-----/ \-----\ ||
|| /-----/ \-----\ ||
||-----/ \-----||

(EDIT- APPARENTLY MY PICTURE DIDNT WORK OUT ON HERE)

What I'm trying to do is display how the string is around both your hands, but with a twist between your hands, making the strings cross.

Pretend your left hand is your film, and your right hand is your field of view of the image youre taking. The place where they cross is your lens.

The distance from the place where they cross, your lens, to your left hand, your sensor, is called your focal length. The string itself is the light.

Now, expand your right hand, so the loop going around your right hand gets larger. Notice as this 'field of view' gets larger, the place where the string crosses gets closer to your left hand. Soooo, as your focal length (distance from your hand to where the string crosses) gets smaller, your field of view (loop around your right hand) gets larger.

Do the opposite. Collapse your right hand. Notice the x moves AWAY from your left hand. The distance from your left hand to the x gets larger. This is your focal length getting larger. Sooooo, you can see as your focal length gets longer, the field of view becomes more narrow.

This is the basic idea behind focal length.


f/3.5-5.6 refers to aperture. That is how much light is being let through the lens. The smaller the number, the larger the aperture, and the more light is let in. The larger the number, the smaller the aperture, and the less light is let in. Often times they refer to lenses that have larger apertures as being "fast" because they collect light quickly. If more light is being let through, then its clear that the light is being sent through the lens faster. This also means you can use faster shutter speed, as it doesnt take as long for your media to record the image.

F stops are sequential powers of the sq rt of 2. We approximate them, so the whole f-numbers are f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, and so on.

Aperture also is a strong modifier to your depth of field. The larger your aperture (smaller the f/number), the shorter depth of field you will have.

Check out this glossary for lots of info about terms we all use:

http://www.usa.canon.c​om …101/glossary/in​dex_a.html

and focal length in general:
http://www.usa.canon.c​om …01/focallength/​index.html
Bruce

staereo, this post should be required reading for any newbie. It's a shame individual posts can't be rated, because this definitely worthy of a star or two.

katiesmom, thank you very much for your kind words.

I was hoping it would be helpful to someone trying to understand these values.

In addition, I read somewhere on the internet a nice analagy for exposure, comparing it to filling a bucket.

Your objective in capturing light is to get a proper exposure. This can be compared to filling a bucket.

Your object is to fill the bucket to the top, without under-filling it, or over filling it.

Your aperture can be compared to how fast your pouring the water into the bucket.
Your ISO can be compared to the size of your bucket.
Your shutter speed can be compared to the duration of your pouring.

If you fill the bucket to the top, you will get a proper exposure. If you change one factor, you must modify one or both of the other two factors accordingly to ensure you do not overfill or underfill the bucket.

I guess im a visual and hands-on learner. Maybe the same types of examples are useful to other people as well.

Bruce