need basic help understanding lenses?

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superhoops1888

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hi im about to buy a sony a350 for £400 from http://www.bestcameras.co.uk/shop/acatalog/Sony_Alpha_A350___18-70_Sony_lens.html which seems a good deal as thats about my limit
it includes a lens of 18-70 (with some other figures)

heres the thing, i havent got a clue about lenses...
ive had a good look on the web but cant find that idiots guide for me!

i needa really simple way for somebody to explain it to me...

now i know it wouldnt be much good, but could i take pictures without a lens?

what does a lens do and what the sizes all about?

if its 18-70 does the camera auto focus the lens to and from 18-70?

is a lens basicly getting closer to the subject?

im not really understanding the whole thing with lenses
please dont go too much into the "f" figures etc unless its realy important to mention them, i just want a basic instruction on the sizes of lenses and what they do...

cheers
will
 
A dslr is basically just a box which has a shutter mechanism inside it, a photo sensor and a pile of electronics which translate what you've taken a photo of.

In order to get the picture onto the sensor there has to be some way of collecting the light and that's your lens. It gathers the light and due to the way the various glass elements inside it are arranged it focusses the picture you see in front of you on the sensor. For the purposes of this answer you must have a lens, no option.

The 18-70 part of the description refers to the focal length range of the lens. 18mm is quite a wide angle and you'll get a wider view of a scene if you use it at that length. 70mm is longer and will allow you to zoom in on the subject a bit more. The longer the focal length of the lens, the more you can zoom in.
 
oh, and welcome to the forums and I'm shifting this to talk equipment ;)
 
the lens is the thing that focuses the light onto the sensor.

the numbers give you a guide to the amount of the view that will be focused onto your sensor and hence become the image.

The higher the number the smaller the amount of the view that you get. So with something like 10mm you will get nearly everything in front of you onto the sensor and have a wideangle/fisheye type of image.
with say 500mm you will have something way off in the distance filling your entire sensor.

So you can think of it as being the higher the number then the more magnification.

Wait a moment and someone will give you a much better explanation.


edit: I remember seeing an image somewhere (dpreview?) that had an image with boxes showing the field of view at various focal lengths from 12mm up. Anyone point me at it?
 
thanks guys
its a wee bit clearer now...

ive always had a point and shoot compact and you use the zoom to move in and out, will this be the same on a dslr?

oh and i know thats we all have opinons etc on good brands etc, but i assume the sony will do for me as price is my main concern...

i also like the fact it has a high spec and will last em a while!

cheers
will
 
ive always had a point and shoot compact and you use the zoom to move in and out, will this be the same on a dslr?
Click to expand...

Yup, it's exactly the same thing..... And yes the Sony will be great.

As would anything from Pentax, Fuji, Olympus, Sigma, Nikon or Canon. Get the one that feels right, does the stuff you want and fits the budget. It's all good. :thumbs:
 
i see there is a fixed focal lenth and zoom lenses

surely if you stop zomming and focus on a subject
the zoom lens becomes a fixed focaul lenth?

or is this far to simple an observation?

william
 
Hi Will

With a point and shoot camera you normally push a button/lever to zoom in or out to get the photo you want.

With a dslr you move a ring on the lens around to obtain the photo you want so you need to hold the camera in a different way than you might be used to. I would think you'd want a zoom type lens so that you can take a range of photo's. The one you've seen of 18-70mm would be ideal for most general photography needs.

I would think a fixed focal length lens would be too restrictive for you - basically it would only give you the one type of photo you could take, so you couldn't zoom in on something you spot as you take a landscape photo for example.

Maybe you could go down to a local camera shop and try holding the camera you're interested in (even if you don't buy from there in the end). There's quite a difference in size and weight between a dslr and a point and shoot and it may make you alter your mind as to the one you want to pick.

Good luck!
 
superhoops1888 said:
i see there is a fixed focal lenth and zoom lenses

surely if you stop zomming and focus on a subject
the zoom lens becomes a fixed focaul lenth?

or is this far to simple an observation?

william
Click to expand...

The lens remains a zoom lens, you just happen to be using a particular focal length :)
 
Just to clarify jool's post, once you have zoomed in or out by moving the focal length ring - ie move from say 17mm (a wide angle, landscape or peope group shot for example) to say 50mm to get a closer shot of something (say an individual within the group), you can then then use the cameras auto focus, just like a point and shoot (by holding down the 'shoot' button halfway on both my 450D & Ixus 75), which will then focus the scene properly for you. Alternatively you can manually focus, though I rarely do this yet (I'm a 6 month newbie).

The 18-70 you are looking at will give you a great starting point, and a great 'walkabout' lens. Once you get hooked though, you'll end up spending a fortune on lenses that fit your preferred photo types!! :D

On a final, personal note, the one thing I wasn't expecting with my kit lens was the lack of focal length compared to my p&s - I was used to being able to zoom on objects which were miles away with my little old camera, whereas the kit lens was limited, so I soon added an 18-200mm to my collection as a walkabout lens. Now, I've got a 17-70 (similar to the one you're looking at) and a 55-250, which gives me the 'zoom' factor I want, whilst keeping the optics sharper.

Hope that helps?? :D
 
Hi the main thing is have a play about with it, your not waisting film it's just a image, try Auto / Man focus , don't change Len's with the camera on, buy a tri pod set up a shot and take as many different shots of the same thing as you can, in manual mode or TV,AV,P, what ever change the apputure/speed, try it in raw, you can then play about with it on the computor, 10mm -20mm wide -Landscape, groups, 18mm -105 wide-ish to groups good portrait lens, then primes and zooms,

regards Mark.
 
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