The most basic question about lenses you're ever likely to hear

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awec

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OK, I'm a total beginner. I see lenses are advertised like 18-55mm, 55-300 (or something) mm etc.

What does this actually mean?:cautious:
 
18mm would be considered quite wide, so you would use that for something that is right in front of you. 300mm is quite far away, so you would use that for something, say 100 metres away. I'm sure someone else will explain it better.

Edit: An 18-55 means that it can zoom from 18mm to 55mm.
 
If you posted in the "Talk basics" section you would get more help I think,but anyway.It is the focal length of the lens.

For example 18mm is quite "wide" and you could get a group of 8 people in one shot.

300 is quite long and if you were stood in the same place as above,with the same scene,,you would get ones persons face rather than the whole group.

Very simplistically put I hasten to add.
 
No.
It is the range of zoom that the lens has,from 18mm to 55mm.
 
Ok, so if 18mm is wide, and 300mm is long, does that mean the lower the number the wider the shot will be, and the higher the number the more zoomed in it will appear?
 
Can anyone find the handy little thing that shows you the same scene with different lenses? You could click on lens a and it would show you the result, then click lens b and show you it etc..
I think it was Sigma that had it on their site but I don't see it. That would probably explain it quite well..
 
awec said:
So the 18-55 is nothing to do with the distance the thing has to be away from you?
Click to expand...

Well, sort of, sort of not. Generally at 18mm you'll be able to focus on something say, 15cm away. At 300mm, you might need to be a few metres away to be able to focus on it. This is a property of the lens in question though, some 300mm lenses will be able to focus closer, others further away.

So while it does sort of have an effect, it's not directly linked.
 
There you go Awec,sorted in the link above.....(y)
 
As stated above, the actual numbers don't have much correlation nowadays.

To put it in laymans terms, the lower the number, the more you see. the higher the number, the less you see.


"When the first lenses where used in cameras, a 50mm lens
was actally 50mm long, a 1000mm lens was actually 1000mm
long. Lenses where basically nothing more than a convex
lens at the end of a tube. A 50 mm lens would be a convex
lens at the end of a 50mm tube, and so on...."
^ Quote from:http://prophotoman.tripod.com/fstop.html
 
Think of it as magnification. The bigger the number the higher the magnification, but the less you can get in frame.

For example, think of photographing a house. To photograph a normal house and get the whole thing in shot you might only have to stand 5-10 meters away with a 10mm lens, but with a 300mm lens you might have to stand 150 meters away (just guessing at figures here).

If you want to take a photo of a bird at, say, 10 meters, you need a long lens (big number) so that the bird fills most of the frame. Shoot with a 10mm lens and you end up with the bird looking like a little dot in the middle.

##edit
Crikey fellas, 8 replies in the time it took me to type that out.
 
Ok, so if 18mm is wide, and 300mm is long, does that mean the lower the number the wider the shot will be, and the higher the number the more zoomed in it will appear?
Click to expand...

Yes, and think of you eye as a 50mm any focal lenth below 50mm will be wide any thing over telepephoto
 
In basic terms its just the zoom. The more mm the further the zoom. :)
 
It's a hang-over from film days - it would make more sense now to start describing lenses in terms of angle of view rather than focal length in mm...especially when considering all the different formats available...
 
the_doctor199 said:
Can anyone find the handy little thing that shows you the same scene with different lenses? You could click on lens a and it would show you the result, then click lens b and show you it etc..
I think it was Sigma that had it on their site but I don't see it. That would probably explain it quite well..
Click to expand...

It is on the Tamron site. I knew it showed what the large picture looked liked at different focal lengths. But I did not notice before, that on the 2 small picture above it you can set the pictures at different focal lengths and see what it would look like at each end of say a 70-200.

http://www.tamron.com/lenses/learning_center/tools/focal-length-comparison.php
 
Arkady said:
It's a hang-over from film days - it would make more sense now to start describing lenses in terms of angle of view rather than focal length in mm...especially when considering all the different formats available...
Click to expand...

That would just upset the Physics geeks who would then have to calculate focal length based on sensor size :p

The real throwback to film days is when lens focal lengths are quoted in terms of equivalent 35mm focal length (regarding angle of view), which is a bit of a snub to anyone who ever shot or shoots with a larger format :geek:
 
awec said:
OK, I'm a total beginner. I see lenses are advertised like 18-55mm, 55-300 (or something) mm etc.

What does this actually mean?:cautious:
Click to expand...


if a man is stood 100 feet away from you and you take a picture at 55mm you will get a pic of him and a lot of the scene around him.

if you take the same picture at 200mm 300mm you will get more of him and less of the scene around him

A lens with 55-300 means you can use either number and all numbers inbetween... zoom in and out

A lens with just one number means you can only use that mm

Simple questions deserve simple answers IMHO :)
 
KIPAX said:
if a man is stood 100 feet away from you and you take a picture at 55mm you will get a pic of him and a lot of the scene around him.

if you take the same picture at 200mm 300mm you will get more of him and less of the scene around him

A lens with 55-300 means you can use either number and all numbers inbetween... zoom in and out

A lens with just one number means you can only use that mm

Simple questions deserve simple answers IMHO :)
Click to expand...

Which basically means that if a person has a fixed 50mm fixed lens, then its up to the person taking the shot to move closer/further to the target to get the composition they want.

There's no fixed distance that you cant take photos from, (except when you're less than the min focus will allow) just that the results will differ.

I think :)

In fact the way I think about it is that when I zoom in to 80mm on my lens, I just think of it as "at that moment" its a fixed 80mm lens. I now have the option of physically moving at that fixed setting to get more or less in. Or I can reduce the zoom to get what I want, but the lens effectively becomes a 60 or 70 or whatever.
 
The best way to look at this that I have seen is.... Get a empty kitchen roll say 200mm long and look through it then cut it in half and look through it (100mm) then cut it in half again (50mm) etc etc. This demonstrates the difference.
 
Historically, and scientifically, what it means is the distance from the film plane/sensor to the rear lens. If you take of your (non internal focussing) zoom lens and look at the camera end - set it on its widest setting and look where the rear lens is, now zoom in and you should see the rear lens move further away. Modern lens design has largely done away with this with the use of multple elements and internal focussing. So,in theory, at 55mm - the rear element of the lens would be 55mm away from your sensor, at 200mm -it will be 200mm away.
Clear s mud
Webby
 
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