Camera Labs

hi,
i need to know what does it signify when i say nikkor AF-S DX 18-70mm f/3.5-4.5G IF-ED , i know the term f/3.5-4.5G IF-ED in it states the focal some thing.... , but in what physical terms, like visual term do u differentiate , and explain the logic of lenses going from 18mm to 70mm , i know the basic terminology but i do not know the scientific explanation to this mechanism of coverage , like if i say 18mm how much in reality say for example physical distance i can cover in focus , and i need to know a detailed explanation to the terminologies given in a lens....

all of that will be very helpful as i need to know them , and wishing that u all will respond to this , iknow its a stupid question , but i need to know the basics .
thank you
sreejith.

The f actually stands for focal length and f/x notation is used to denote the maximum aperture size. On a lens the f/x number denotes the maximum aperture possible. e.g 50mm f/1.8. On a zoom lens where the focal length is variable ie 18-70mm then the maximum aperture usually changes as you zoom in and hence the max aperture range is also written as f/3.5 to f/4.5 (eg f/3.5-4.5). Zoom lenses with one f/x number have a constant max aperture throughout the zoom range and are usually expensive as it costs more to manufacture.

http://www.bestphotolessons.com/index.php?s=content&p=Camera

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Canon EOS 400D, EF-S 18-55mm, EF 24-105mm f/4L IS USM, EF 50mm f/1.8 MK I, EF-S 10-22mm, EF 70-200mm f/4L IS USM, EF 28mm f/1.8, EF 85mm f/1.8
Canon 430EX II, Manfrotto 055CXPRO3, Arca Swiss P0
Panasonic GF3, Panasonic 20mm f/1.7, Olympus 45mm f/1.8

MY FLICKR!

If memory recalls the F ratio is lens diameter/sensor diameter. So the lower the F number, the larger the lens is compared to the sensor. This also explains why full frame lenses have to be bigger than cropped frame lenses to get the same aperture.

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I take pictures so quickly, my highschool was "Continuous High".

Nearly right - it's the focal length divided by the effective lens diameter (taking account of the iris). But these sort of questions are easily answered by the OP doing his own research, an essential skill for a student and an engineer.

If Googling doesn't do it then, as long term members here know, a good reference site for the mechanics (as opposed to Gordon's DSLRTips which concentrates more on the practicalities) is CambridgeInColour.

Bob.

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OM-D E-M5 + ED 12-50mm, H-PS14042E, H-F007014E, L-RS014150E, M.ZUIKO DIGITAL 45mm 1:1.8.
Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.

hi,
thanks bob, and everyone who posted , well i always knew somthing about the topic i just need certain confirmation on those , as a fresh mechanical engineer , i just needed to study something like this it is an amazing thing to learn the mechanism , but thanks again i will ask only
those questions which are not available on sites after googling ,
and Mr.gordon sirs dslr tips also is very helpfull and also the site cambridgeincolour is a nice site to refer to
thank you
sreejith

same thing it means in just about every other context.

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I've upped my Iso, now up yours.
Nikon D700, Nikon D80, Micro Nikkor 105 f2.8 AI-S,Nikon 85mm 1.8D, Nikon 50mm 1.8D, Nikon 35mm F2D, Nikon 16-35 f4 VR, Nikon 24-70mm F2.8 AF-S, Nikon 70-200VRII, Nikon 70-300mm VR, 300mm f2.8 AI IF ED, SB-800, SB-900. Noiseware pro,NIK Dfine, Nik Colour Effex, Nik Sharpener Pro

Here is what I don't understand:

Increasing f-numbers, in one-stop increments; each aperture has half the light gathering area of the previous one.

So we have:
F1.4 - F2 - F2.8 - F4 - F5.6 and then F8?

If this was a standard IQ test and you were to guess the next number in the series:
1.4 - 2 - 2.8 - 4 - 5.6 ___ Then you'd choose F7.6, would you not?

Cheers

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Nikon stuff and other stuff, but not nearly as much stuff as I really want!

It's logarithmic, not linear, Lahlah

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I take pictures so quickly, my highschool was "Continuous High".