what does lens specification number means?

[legolas wood]

Hi
Thank you for reading my post.
after reading some articles i find that

f-number show amount of light that can reach the CCD. if we use a bigger f-number that we should use an smaller shutter number to prevent over exposure in normal light.

what i can not understand is

numbers like 18-55mm and 50-200mm

what do they mean and what is thier usage?

Thanks

 

[Petteri Sulonen]

Focal length.

[ http://www.dpreview.com/learn/?/Glossary/Optical/Focal_Length_01.htm ]

Petteri
--
http://www.prime-junta.net/
http://www.flickr.com/photos/primejunta/

 

[Barrie Davis]

Hi
Thank you for reading my post.
after reading some articles i find that
f-number show amount of light that can reach the CCD. if we use a
bigger f-number that we should use an smaller shutter number to
prevent over exposure in normal light.

Actually, it is a smaller (lower) f/number that lets in more light....

[Example of a smaller f/number ..... f/2.8]

...and a larger (higher) f/number that lets in less light....

[Example of a larger f/number..... f/11]

Similarly it is the LOW numbers which let in MORE light with shutter speeds...

[Example of a low shutter speed.... 1/4 second]

..and it is HIGH numbers which let in LESS light with shutter speeds...

[Example of a high shutter speed... 1/250 second]

what i can not understand is

numbers like 18-55mm and 50-200mm

what do they mean and what is thier usage?

Those numbers tell you the range of focal lengths the lens can provide when zooming.

The low number is how Wide-angle it can go (getting a big scene into the picture) and the high number is how Tele-photo it can go (filling the whole picture with small subjects at a distance.)

Zoom lenses are good, because they can be set at intermediate f-lengths, too ... so you can zoom to frame your subject without so much walking about.

But, be careful!

It is good to have an extended range of f-lengths in one lens... but a good SHARP lens, that also has a big f-length range, will very likely....

a) be expensive,

b) be large and heavy to carry around,

c) NOT have a wide aperture (low f/number.. like f/2.8) for dim light shots.

I hope this helps.
--
Regards,
Baz

 

[legolas wood]

thank you very much. very good explanation and a very good link.

So, a 18-55 and a 50-200 lens is almost essential for intermediate photographer because they can do telephoto and also wide angle shot because of 18-55 lens.

thanks

 

[Marwood]

You'll find that most manufacturers tend to sell their dslrs with a standard kit lens. This tends to be in the 18-55 range, though some also do 18-70s. (Then there are the Olympus

This is a standard zoom length which goes from moderate wide-angle to moderate telephoto. It's a very useful lens to have and for most people will be the lens they use most often.

Adding a telephoto zoom is an option but I wouldn't say it's essential: it all depends on what sort of photography you're taking. That said, there are often good deals on buying the 55-200 when you buy the camera, in which case it can make a lot of sense.

 

[Marwood]

Sorry, went off to check the details of the Olympus lenses, forgot, came back and posted.

What I was going to say was that the most common Olympus kit lens is a 14-42mm but because of the different sized sensor, they're effectively the same range as the 18-55 that you'd get on a Nikon, Canon or Pentax/Samsung.

 

[David Hughes124436]

Trouble with zoom lenses is that they make things a little too easy and so you miss pictures. When I used a couple of primes (meaning lenses that weren't zooms) I would have to walk about a bit to get the picture I wanted and walking about meant I saw things differently and got several bites at the cherry. With zooms I have noticed people stop, look and zoom in or out and take the picture. Without they might just have seen something better as they looked for a position to take the picture they'd imagined.

I've noticed that the smaller zooms (x2 or x2½) on P&S cameras often get better pictures, hence my theory. Get a dSLR type and you cover everything from 28 mm to 280 mm but miss a lot.

Just my 2d worth, David