Lens numbers help.

Sony_SoFar

Sony_SoFar

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Lewis
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Hi all,

Don't really understand much about the numbers on the lenses both the 18-55mm for example and also when there are 3.6-5.6 etc i have no idea about that.

The 18-55, 70-200 etc are for the amount you can zoom in although im not sure how far I could zoom in with a 70-200 mm lens on a camera.

The decimal numbers make no sense to me what so ever...so all help is good help



Thanks in Advance


Sony_SoFar:cuckoo:
 
The focal length (18-55) will begin to mean more to you in time. It's one of those things that's baffling at first but soon you'll start to realise which lens you need to do what. The decimal numbers are how much light the lens lets into the camera. The smaller the number the more light is let in. The range (3.5-5.6) means that at 18mm the lens is f/3.5, and by the time you get to 55mm the lens has gotten darker to f/5.6.

All of this stuff is online after a quick Google search though, it'd probably be easier to understand if you read through it at your own pace.
 
Just them 3 lines has given me a rough idea, and is more than what I knew. Thanks for the advice. I'll have to give google a look :thumbs:
 
Also try having a look at Bryan Peterson's book "Understanding Exposure". It's great for beginners and explains all the ins and outs of those numbers!
 
Heres a fun one for ya, If you had a 50mm f1.0 lens (expensive, but they exist) the hole the light goes through would be 50mm diameter.

In my 50mm f1.4 lens the hole is about 35mm... 50/1.4 =35 (ish)

At 55mm f5.6 the hole will be... just under 10mm and you quite clearly can't fit as much light through a 10mm hole as a 35 or 50mm hole

Keep in mind thats the diameter, area of a circle = Pi * radius²

So compare a 50mm f2.8 and a 50mm f4.

f2.8 = 17.85mm diameter = 8.9mm radius = 250mm²
f4.0 = 12.5mm diameter = 6.25mm radius = 122mm²

roughly double the area = double the light. But its not quite right? reason is i've taken the f2.8 as 2.8, in reality its 2x the square root of 2 (square root of 2 pops up a lot in photography) taking that as our number we end up at 245mm²

Okay, i've just used a 50mm example, a 100mm f4 lens will have a larger aperture than a 50mm f4 yet the exposure doesn't change... wtf? but have a think about what you see through the lens, the 100mm lens will see much less, the 50mm lens is pulling light from a wider area. Having the aperture numbers arranged as they do provides a very easy system to figure out how to expose with different focal lengths.

Maths is fun!
 
You have just killed my brain 100%. It all sounds rather complex like that. But I have a rough idea about them now. I suppose if I get into photography heavily later on them I will have to look into it more but at the moment i'm just using it as a toy really.
Them f1.0 50mm lenses are like £100 ish...OUCH!!
 
Thanks for that, its superb. Just messing around and as soon as I mess it up I cant get it back :(!!
Im sure using a real camera in real situations would help me no end. Its saved in my favourites anyway :thumbs:
 
Sony_SoFar said:
You have just killed my brain 100%. It all sounds rather complex like that. But I have a rough idea about them now. I suppose if I get into photography heavily later on them I will have to look into it more but at the moment i'm just using it as a toy really.
Them f1.0 50mm lenses are like £100 ish...OUCH!!
Click to expand...

Lol, not quite...

Besides, £100 for a lens is nothing, you'll be spending a damn site more than that if you get into it.
 
TCR4x4 said:
Lol, not quite...

Besides, £100 for a lens is nothing, you'll be spending a damn site more than that if you get into it.
Click to expand...

£100 for now is more than enough I think! The camera would be worth less than the lens! Is this a normal thing??
 
Sony_SoFar said:
£100 for now is more than enough I think! The camera would be worth less than the lens! Is this a normal thing??
Click to expand...

Yep perfectly normal until you get onto pro bodies. All my lenses bar 1 cost over £600 new. The 24-70 still sells for well over £1k. It's the lens that is the most important bit. A bad lens on a good body equals a bad image.
 
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