Lens Explained

scrag68

scrag68

Suspended / Banned
Messages
180
Name
Craig
Edit My Images
Yes
Guys - could someone explain what the numbers on a lens is in more detail or post a link to help.

I know theres many types of lens and prices but i would like to get an understanding of what the numbers me eg.

70-300, 18-55, 18-70, 18-105 and 50 etc etc

I know that this is all to to with width and length but you see a lens and theres just a couple of numbers different and you find that the price goes up and down.

Thanks Guys and Gals
 
the numbers such as 70-300mm , 18-55mm are followed by mm as they are the zoom length, the 50 with the circle and line through it is the thread size? I am guessing Im sure someone will come along and explain it much better :P
 
scrag68 said:
theres just a couple of numbers different and you find that the price goes up and down.
Click to expand...

This is probably more likely aimed at the f/ number (aperture number). Generally the lower the f/ number the higher the price, e.g. a 70-200mm f/2.8 lens will cost more than a 55-200mm f/3.5 - f/5.6 lens. The f/2.8 aperture is constant across the range as opposed to the other lens that would have a maximum aperture of f/3.5 @ 55mm and f/5.6 @ 200mm.

'Faster' lenses are desirable for a number of reasons - freezing subjects in motion, low-light shooting, etc.

Does that make sense?
 
70-300 for example is the focal length > 70@wide end....300@ long end it refers to the distance from front element to sensor .

you'll often find a lens describes as for example 70-300 f4-5.6
explanition


at 70mm the maximum aperture is f4 whilst at 300 the maximum aperture is f5.6.

some lenses ( the expensive ones ) have a constant maximum aperture ,for example 70-200 f 2.8 ..

this might help .

http://www.cambridgeincolour.com/tutorials.htm

[ EDIT ]

third link down on this site
 
sdb123 said:
This is probably more likely aimed at the f/ number (aperture number). Generally the lower the f/ number the higher the price, e.g. a 70-200mm f/2.8 lens will cost more than a 55-200mm f/3.5 - f/5.6 lens. The f/2.8 aperture is constant across the range as opposed to the other lens that would have a maximum aperture of f/3.5 @ 55mm and f/5.6 @ 200mm.

'Faster' lenses are desirable for a number of reasons - freezing subjects in motion, low-light shooting, etc.

Does that make sense?
Click to expand...

Its making a little Sense but for example what does a 70-200 do that a 55-200 doesnt is the 70 and the 55 the width and the 200 the length, what does the smaller number refer to?

Sorry if im not explaining myself very well still a newbie and cant you tell :lol:
 
The 70-300 18-55, 70-200 etc are the focal lengths. On your camera, about 35mm is the view you see with your eye, anything above is smaller than you can see(but bigger) and anything lower shows more than you can see.

f number is the other thing, which is a ratio of length to width, the lower the number the bigger the apperture, the more light enters the lens and the quicker you can go with your shutter speed(the larger appertures also decrease the area in focus)

as said above, the thread size of the front element(for filters etc) is normally listed as well.

Lens prices arent just governed by focal length and apperture though, there is lots of other things involved, like barrel distortion, different elements inside the lens, etc etc etc...

edit.
the 70-200 will be a professional quality lens, most likely with a fixed aperture, where the 55-250 is a budget lens(but still very good)

make sure you check the prices before buying though, and there are some good quality lenses out there for peanuts.
 
daftbugga said:
70-300 for example is the focal length > 70@wide end....300@ long end it refers to the distance from front element to sensor .
Click to expand...

I don't want to add any confusion here but this part isn't correct....it's a lot more complicated than that.

Bob
 
With say a 55-200 you can be closer to the subject and the camera will still focus. But with a 70-200mm you have to be further back for it to focus.

That make sense?
 
rtjdesign said:
With say a 55-200 you can be closer to the subject and the camera will still focus. But with a 70-200mm you have to be further back for it to focus.

That make sense?
Click to expand...


Yes getting there now thanks Guys and Gals i :love: this Forum everyone is glad to help.


thanks again :clap:
 
rtjdesign said:
With say a 55-200 you can be closer to the subject and the camera will still focus. But with a 70-200mm you have to be further back for it to focus.

That make sense?
Click to expand...

That's not really true.

What I think you mean is that the 70-200, with a minimum focal length of 70mm you will have to be further away from the subject than with the 55 in order to get it in the frame.

70 - 200 means that it is a zoom lens and provides focal length options at both ends and all points between.

The camera will still focus at any distance (as long as you are outside the minimum distance for the lens, which will typically be around 1m for these lenses)

Essentially the amount the image is magnified is related to the focal length used. You will get greater magnification with the 250 at the extreme end. However, as has been mentioned, the build quality of the lens may not be as good and therefore the image quality also may suffer.

The points on aperture are also important to bear in mind as, depending on what you are shooting, it can make all the difference.
 
This thread answers a lot of questions i had but didnt want to ask:lol:, its a b****r being a beginner. I had often wondered why the price difference between lenses, i realized about build quality etc, but didnt know about the F number bit. Thanks guys:)
 
fernface said:
This thread answers a lot of questions i had but didnt want to ask:lol:, its a b****r being a beginner. I had often wondered why the price difference between lenses, i realized about build quality etc, but didnt know about the F number bit. Thanks guys:)
Click to expand...

That was a bit like me at first waiting for someone else to ask the questions. Hey nothing to be Embarrassed about everyone was a newbie at one stage :)
 
I know what you mean. Its a pity really there is not a place on TP where beginners(hate newbie etc) could post and perhaps help each other, with an overview by the more expert to come in to help if they felt disposed to do so. Would avoid cluttering up this "talk equipment" bit. Great place for information though:)
 
that what the whole forum is for, ask the question in here and people will help, a seperate forum might get missed by a few people and a fair few just work off the homepage anyway;)

just post the question, the only stupid question is the one not asked
 
You must log in or register to reply here.
Back
Top