Lens Basics - Help Please

rpsmith79

rpsmith79

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Please bare with me as this is probably the most noob of noob questions, but can anyone explain to me in simple terms the basics of lenses

What i mean is 35mm, 50mm, focal length, the difference with 4/3's, Prime??

I have an Olympus E-520 with the stock lens, but i had a play with a mates camera who had a 50mm Prime lens (what does Prime mean :shrug:), i liked what i saw so i bought one and i really like using it, but i have no idea how or why it does what it does

I'd like to look for different lenses but i have no idea what i'm looking for as i don't really understand what all the numbers and terms mean

About the only thing i do understand is that the 50mm Prime is that i can set the apature to give me a very shallow DOF (which i like using), the only thing i don't like is how close everything looks (is this Focal Length :shrug:)

Sorry for the noobish questions, but i really can't seem to get my head around it
 
prime means no zoom. zoom means the lens has the ability to make subject appear close or further away. this zoom action is achieved by varying focal length. prime is fixed at a single focal length.

take a typical prime lens label: 35mm f1.8. lettering varies by brand, but the two numbers seen here are present on all lenses.
-35mm means its focal length is 35mm.
-f1.8 means the lens' maximum aperture is at f1.8.

a typical zoom lens label goes like this: 18-55mm f3.5-5.6
-18-55mm is the range of focal length. at 18mm you seem further away from the subject, and see more of the scene. at 55mm you seem closer to your subject.
-f3.5-5.6 means maximum aperture changes depend on focal length you are using. f3.5 at 18mm, f5.6 at 55mm

there is also crop factor you got to consider when choose lenses. because there are many different sensors, we need a standard. old 35mm sized film is chosen, it is known as full frame, they are used on high end cameras like Canon 5D mark3 and Nikon D800. you say it seems too close it is because using a 50mm on a micro 4/3 looks like using a 100mm on a full frame. micro 4/3 has a crop factor of 2, so you multiply 50mm by 2 to get what it would feel like on a standard full frame camera.
 
Many thanks, that has cleared up quite a few things

So my next question, i presume there is a limit to the focal length/aperture size of each type of lens

In that i mean, can you get an 18mm lens with a maximum aperture of f1.8 (i presume not)

Also, if my kit lens is an 18-55mm, is that real focal length, of is that subject to the crop factor, and if not, how would i know if i were to buy a new lens if i need to apply a crop factor or not
 
The limitation is size and cost. The f number if calculated by dividing the focal length by the maximum size of the hole the aperture blades can provide.
So a 50 f1 lens needs a max hole that is 50mm (50 / 50 = 1) This means the lens barrel has to be much larger, more complex, larger lenses etc,. and also increases the cost of manufacturer (a lot!)
 
Your 18 - 55 kit lens has not had a crop factor applied and is how it would be on a full frame camera as per Wuyan's comment.

You would need to multiply by whatever crop your camera is to get the equivalent numbers for comparison.
 
ernesto said:
Your 18 - 55 kit lens has not had a crop factor applied and is how it would be on a full frame camera as per Wuyan's comment.

You would need to multiply by whatever crop your camera is to get the equivalent numbers for comparison.
Click to expand...

So hypothetically speaking, if i wanted a Prime lens with the same field of view as my kit lens set to 18mm, i would be looking for a 9mm lens, or are you saying if i bought an 18mm Prime lens it would have the same FOV

What i am ultimately after is a wider angled FOV than my 50mm (possibly even wider than my kit lens at 18mm), but as i like taking shots at night and shots with a shallow Depth of Field, i would want a lens with a large aperture, but i wouldn't even know where to start looking

Oh, and i wouldn't want to be spending a fortune either, bearing in mind my 50mm Prime cost me about £25 second hand (manual focus only)
 
there is a limit for each lens. focus length range is labelled as it is: "18-55mm". widest at 18mm, most zoomed in at 55mm. aperture limit is labelled as largest possible aperture, because minimal aperture usually doesn't matter as much, all lenses can do smaller than f/16. the aperture range seen on lenses (eg. f3.5-5.6) is maximum aperture, varying depending on focal length.

notice i reference 18mm as wide and 55mm as zoomed in. basically the lower focal length is, the wider field of view. this is important as when we talk about crop factor and full frame equivalent focal length, it only really means equivalent field of view. every other lens property doesn't change (physical focal length and aperture), but that's not important at the moment, it's just something most people forgets.

crop factor is dependent on camera, on micro 4/3 cameras the crop factor is always 2x. so 18-55mm is equivalent to 36-110mm in terms of field of view compared to a same lens on full frame.


keep in mind the full frame standard lengths: 28mm is a standard wide angle, 50mm is considered as a all around standard. ~80 is considered a portrait length. 100mm or more is considered telephoto. you can work your way back from this to see what focal length you want.


here's a good site that i found very useful when i started looking at lens:
http://lenshero.com/
 
rpsmith79 said:
So hypothetically speaking, if i wanted a Prime lens with the same field of view as my kit lens set to 18mm, i would be looking for a 9mm lens, or are you saying if i bought an 18mm Prime lens it would have the same FOV
Click to expand...

your kit lens at 18mm is equivalent to 36mm on full frame. ok, if you are only looking within your camera lens ecosystem, then don't need to worry about crop factor. so buy a 18mm for same field of view.

rpsmith79 said:
What i am ultimately after is a wider angled FOV than my 50mm (possibly even wider than my kit lens at 18mm), but as i like taking shots at night and shots with a shallow Depth of Field, i would want a lens with a large aperture, but i wouldn't even know where to start looking
Click to expand...
for shallow depth of field, you need a long lens and/or a large aperture. try lenshero website and filter by large aperture. (low f number)
 
rpsmith79 said:
So hypothetically speaking, if i wanted a Prime lens with the same field of view as my kit lens set to 18mm, i would be looking for a 9mm lens, or are you saying if i bought an 18mm Prime lens it would have the same FOV

What i am ultimately after is a wider angled FOV than my 50mm (possibly even wider than my kit lens at 18mm), but as i like taking shots at night and shots with a shallow Depth of Field, i would want a lens with a large aperture, but i wouldn't even know where to start looking

Oh, and i wouldn't want to be spending a fortune either, bearing in mind my 50mm Prime cost me about £25 second hand (manual focus only)
Click to expand...

18mm is 18mm whether zoom or prime, for now i wouldnt worry too much about crop factors, to go wider than 18mm a quite few on here use 10-20mm sigma but they arn't cheap
 
As your camera is a 4/3 system camera, this might be useful for you

http://www.four-thirds.org/en/fourthirds/lens.html

With this system, a 25mm lens is regarded as standard; this means it give a natural angle of view. Shorter than this is wide angle, longer is generally refered to as a telephoto.

Some zoom lenses are wide angle only eg Olympus 7-14mm

Some are telephoto only eg Olympus 50-200mm

Some start at wide angle and finish as telelphotos, these are generally known as standard zooms

To get the effect you mentioned in your OP, you might want the 25mmf1.4 lens., but it's expensive

Unless you have previously used 35mm cameras, I'd ignore any references to crop factors as they are misleading.
 
mortimerhill said:
Unless you have previously used 35mm cameras, I'd ignore any references to crop factors as they are misleading.
Click to expand...

yeah, i started on 35mm film, relate everything to 28-80mm, my very first camera's kit lens. :D


as i said, if you are only look within a single system, then no need to consider crop factor as it won't affect the lens.
 
Cool, cheers for that Simon, that makes sense i suppose

Is there any sort of lens i could be looking at that is a manual focus only (like my super cheap 50mm Prime) that would give me the desired effect, or am i only looking at auto focus lenses that will be uber expensive

Also, looking into my Olympus E-520 more closely, it appears the kit lens is a 14-42mm f3.5-4.6 (camera is at home, so will double check when i get in), so i'd want to be looking at something lower than 14mm to get any wider field of view and larger aperture

Looks like things are about to get rather expensive :'(
 
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