Newbie lense question

[Craig_C1976]

Hi all,
Could anyone explain lenses to me? :?
I'm quite new to all of this and have a A70 but I'm noticing the zoom (4x) can be quite restrictive at times (forget digital zoom). The more i've been reading on these boards from people with SLR's they are all talking about lenses, particularly the F number and mm.
I think the a 70mm lense would be wide angle right? And say a 300mm is telephoto/zoom.
Sorry if I appear a little dense here, but would a say, 28-300mm lense mean that this would equate to a 4x zoom on a compact camera (obviously with better results on the SLR) - like a ratio almost?
If this is the case, the lense looks really long for only zooming 4x?? I've got to be wrong here surely :wink: I'm sure there's more to it.
Going onto the F number. What does a 'fast' lense mean? Is it for quick focusing, like for use at motor racing events? Say a zoom lense at f2.4 would be 'fast' for quick zoom and focus? :?
Thanks for any help, as I say, i'm just trying to advance a little here, my composition etc is improving , but I'd just like to know a little more about the lense on an SLR for the future (dream buy and all that :lol: )
Craig.

[Jesper]

First of all, forget about the "4x zoom" terminology. It doesn't really tell you anything. It just tells you the difference between completely zoomed out and completely zoomed in, but if you don't know how wide the wide end is, or how long the long end, the "4x zoom" isn't very useful information.

70mm is not wide angle; on the contrary, it is a medium telephoto lens. On a standard film camera, you can consider a focal length of 35mm and shorter wide angle. Between 40mm and 55mm is "normal" (i.e. about the same field of view as what your own eyes see). 70mm and longer is telephoto.

An 28-300mm lens goes from the moderate wide angle to long telephoto range. If you want to say it in the "so many times zoom" terminology, it would be about an 300/28 = 11x zoom lens. But don't make the mistake that the more zoom a lens has, the better it is. On the contrary, lenses that cover such a large range most often are not the best quality lenses, because the engineers needed to make some compromises in the design to get the lens to cover the entire range. Fixed focal length lenses (also called "prime" lenses), which don't zoom at all, is almost always superior to zoom lenses in terms of optical quality.

When a lens is "fast", it does not mean that it focuses quickly. The f/stop number doesn't have anything to do with auto focus speed. The f/stop number indicates how large the aperture of a lens can be made. "Fast" lenses have large maximum apertures, which means the f/stop number is smaller (to make it a little more confusing...). So a lens that goes up to f/2.8 is "faster" than one that goes only to f/4.0. Where the term comes from: when you use a larger aperture (smaller f/stop number), the lens lets in more light, so that you can choose a faster shutter speed.

[Craig_C1976]

Jesper,
Thanks for the reply. Cleared up a few things nicely.
Yeah, I knew about the f number referring to aperture etc, but never realised (kind of obvious now :oops: ) that a 'fast' lense allows a faster shutter speed. Looks kind of a stupid question now. :lol:
Thanks a lot,
Craig.

[Andy_T]

Craig,

you can increase the zoom of your lens with a lens adapter and a conversion lens.

Basically that work like a kind of magnifying glass that you screw in front of your lens. They normally have some indication (e.g. x2.0) to indicate the factor by which they either shorten the focal length or make it longer.

There are both wide angle adapters (e.g. Canon WC 52 x0.7) taking the wide end of your camera from 35 mm to 25 mm and tele adapters (e.g. Canon TC52 x2.4) converting the 105 mm tele end into a 250 mm ... if you got these two, you'd have a 10x zoom.

Best regards,
Andy

[Craig_C1976]

Hi Andy,

Thanks for the reply. I was aware of these attachments for the Axx family, although I don't think I'll bother. I don't really want to invest anymore $$ in the camera for now, i'd rather improve my theory, take more pictures and maybe one day upgrade to an SLR once I get a lot more technical knowledge while putting up with my 3/4x zoom....i've got a lot of learning to do first.
I knew about the x10 factors etc, but just couldn't relate this to mm lengths when I hear people talking about their SLR lenses. I'm getting there now though. I think popping into my local store and actually looking through these lenses will help me out.
I've bought a couple of great books at the weekend which is keeping me busy.
Thanks again,
Craig.