Another Newbie Lense Question

[AimeeJ]

Sorry for the abundance of questions, but I'm just trying to get a good handle on the whole lense scene. Can someone give (or point me towards) a good explanation of lense focal length. Specifically, the aspect that I am currently confused on is as follows:

When looking at an all inclusinve list of Nikkor lenses, I see under the category of standard zoom lenses the 18-200mm. Then under the wide angle section I see 20 mm(amongst others). How is the 20 mm encompassed in the 18-200 range different from the 20 mm listed under the wide angle section? Obviously, this is just one example as there are many with similar numbers.

[Tee Why]

This is a Canon site but if you click on "EF Lenses 101" it may get you started.
http://www.usa.canon.com/consumer/controller?act=MultiMiscPageAct&key=Learning_Station&fcategoryid=2533

[AimeeJ]

Thanks for that link. As a beginner, it's just a little confusing when I see 2 lenses that are similar in focal length but the physical dimensions of the 2 lenses are SO different. I'm sure it will get easier once I do more research and have more hands on experience.

[BikePilot]

Focal length is just the amount of "zoom" or whatever you want to call it (how far away it looks like you are from your subject). 20mm is always 20mm regardless of whether its a 18-200 at 20mm or a 20mm prime. Now, different cameras will use lenses differently, a full frame (D3, 5D etc) will use all of the lens area, a crop sensor camera (like a D300, 40D etc) uses a smaller sensor relative to 35mm film size or full frame dslr. This means that that the effective focal length is longer. I think a D300 is 1.6x on the crop factor. So a 160mm lens on a D3 will give the same field of view as a 100mm lens on a D300.

The other thing to pay attention to is the f-stop. Smaller numbers mean the lens lets in more light and allows you to use higher shutter speeds and a narrower depth of field for a given exposure.

Lastly, pay attention to image quality, some lenses will produce softer images, distorted images, less contrast etc than others. In general what you buy with more expensive lenses is better iq and often lower f-stops (lets more light in). All else equal prime lenses (lenses with only one focal length) tend to be sharper and have better iq than zooms.

[AimeeJ]

My understanding of the lenses is much better now...I just am so torn as to what route to go when purchasing my first lense. I think the 70-200 Nikkor would be nice to have...but I can't help but thank that such an all-encompassing lense might skimp out on some details. Should I just buy 2 or 3 more specific lenses or just get the one that seems to cover the most range. I guess I will keep researching and hopefully it will come to me.