Aperture question - lens not software (Nikon D40) - Help please :)

[grahamtearne]

Hey guys, I'm in the market for an entry DSLR and I am very tempted with the Sony A200, depending on how much money I can spend I may look at the A300 for live view or the Canon EOS 1000D I think its called, either way this wont be till October so anything can change.

During my research though I played around with my friends new Nikon D40 with the kit lens. On the internet and other material etc it says the kit lens has an aperture of f3.5-5.6 and even mentions these numbers on the lens itself. However when playing with the aperture mode it went up to 22 or something which really confused me as I thought it could only do 3.5-5.6.

I am a newbie to DSLRs and this will be my first one. I will be coming from a Lumix LX2 which I bought to learn the basics of manual controls as it has some great manual features. I now want to upgrade to a DSLR but lens research has confused me somewhat.

If someone could please inform me of why it was possible for the D40 to shoot at apertures above what the lens was advertised at it would be a great help in aiding my on going research towards my first DSLR.

Thanks

 

[swiftaw]

the f3.5-5.6 is referring to the largest aperture setting that the lens will do. On the other end, the smallest aperture it will do is probably f/22

 

[grahamtearne]

Thank you for the quick reply. I thought it was the range! haha. Ah well good to know, that makes much more sense now. Thank you.

 

[rogersmj]

It is a range, sort of. It's the maximum aperture range. On the 18-55mm kit lens, that means at 18mm the widest you can open the lens is f/3.5, and that decreases (linearly, as far as I can tell) until you get to 55mm, at which the widest it will go is f/5.6.

 

[ChrisA]

If someone could please inform me of why it was possible for the D40 to shoot at apertures above what the lens was advertised

f/22 is not above f/3.5.

The f-stop number is just the lens' the focal length divided by the diameter. So the f-number becomes big when the iris contracts and makes the effective diameter smaller. In other words f/3.5 or f/22 tells you the effective diameter of the lens if you know "f".

The way to think about f-stops is that it acts like a value on a water tap. It controls the rate that light gets through the lens. f/22 is a really, really small hole and not much light gets in.

Now it should be clear. Physically it is easy to make a lens smaller by using an iris. This is also why those "fast" f/2.8 and f/1.4 lenses cost more -- bigger chunks of glass