I'm Confused - mm?

Fireblade2K4

Fireblade2K4

Fireblade2K4

Associate
Joined
9 Nov 2004
Posts
1,691
Location
West Midlands
Ok, I've only recently gotten into photography, I've moved from a Canon A95 to a Canon S3 IS and thus far I have to say I am loving it, just the sheer satisfaction I feel after getting some nice shots, its a real joy! Plus posting them on here and getting positive and constructive feedback makes it all the more enjoyable.

So far i've pretty much managed to figure out what most aspects of photography and taking pictures are about and how they effect the overall shot, all except one, well one so far anyway unless I come across some others...it is "mm" or "focal length"

Now I will be moving to D-SLR soon, most of the people on here using a D-SLR when talking about lenses always talk in "mm" which I know is millimeters, but how do you work out what a lens is going to offer you from the "mm" of it. For instance using one off the top of my head, the Canon 18-55mm or Nikon 18-70mm what are they going to offer, how much zoom will they give me?

This might sound stupid but its just something I can't get my head round so would someone be kind enough to explain it to me please, I know it has something to do with the focal length but how do you know what these "mm" are going to give you?

Hope this makes sence as I found it a bit difficult to put into words.

Cheers
Stu
 
The best way to get your head round it is the field of view. This is how much you can see. At the wide end, you can see lots, zoomed in you can see little, but in more detail.

Your A95 had 38-114 mm equivalent
Your S3 has 36-432 mm equivalent

What this means is that your S3 can zoom in far further.

On SLR lenses, the mm focal length is for a film camera, or a d-SLR with a sensor the same size as a piece of film. However, most d-SLRs have a sensor that is smaller than a 35mm piece of film, so in effect this crops the image, and 'zooms' you in more on the image. Therefore, on a D-slr, you have to take the mm of the lens and multiply by 1.5 for Nikon and 1.6 for Canon to get the 'equivalent' focal lengths. So,

Canon's 18-55 becomes 28.8-88
Nikon's 18-70 becomes 27-105

However the greatness of D-SLRs is the flexibility, in that you can change lenses, and so focal lenths :)

Hope that helps matters!

Kimmett

edit: Too slow!
 
http://en.wikipedia.org/wiki/Focal_length

It's the focal length of the lens. Measured in millimeters (mm), it gives an indication of the magnification power of the lens. Higher = more. All you basically need to know is that on a full-frame SLR camera (all film SLR and some high end DSLR's), 17mm is about as wide as you get, 50mm normal point an shoot type, 105mm is portrait stuff, and then after that you're really into telephoto territory.

Most DSLR's add a complication because their sensor is smaller than a film negative. This has the effect of magnifying everything about 1.6 times (crop factor). Therefore a 50mm lens on a DSLR like the canon 350d will actually have the same magnification as an 80mm lens on a full-frame camera. As a result, the lenses can be much wider wihout cropping the corners, and therefore the lowest you can get on a 1.6x crop DSLR is about 10mm (the sigma 10-20 and the canon 10-22 are the most common). These won't work on full-frame cameras as they're too wide, and actually probably won't fit.

Hope I've covered most things.
 
KIMMETT said:
The best way to get your head round it is the field of view. This is how much you can see. At the wide end, you can see lots, zoomed in you can see little, but in more detail.

Your A95 had 38-114 mm equivalent
Your S3 has 36-432 mm equivalent

What this means is that your S3 can zoom in far further.

On SLR lenses, the mm focal length is for a film camera, or a d-SLR with a sensor the same size as a piece of film. However, most d-SLRs have a sensor that is smaller than a 35mm piece of film, so in effect this crops the image, and 'zooms' you in more on the image. Therefore, on a D-slr, you have to take the mm of the lens and multiply by 1.5 for Nikon and 1.6 for Canon to get the 'equivalent' focal lengths. So,

Canon's 18-55 becomes 28.8-88
Nikon's 18-70 becomes 27-105

However the greatness of D-SLRs is the flexibility, in that you can change lenses, and so focal lenths :)

Hope that helps matters!

Kimmett

edit: Too slow!
Click to expand...
Ok so would I be right in saying that a 70-300mm lens on a Canon would actually give a focal length from 112mm - 480mm?

Stu
 
basically a lens that is say 18-55mm will give a field of view anywhere in between 18mm and 55mm -or as you would say you could zoom in and out between 18&55mm

because at 18mm the distance is short from the sensor the field of view or angle of view is larger- so you will fit more in

at 55mm the distance from the sensor is longer and the angle of view becomes narrower, giving the effect of magnification or what some people describe as "zoom"

so a 100-400mm lens can zoom anywhere between 100mm & 400mm and at 400mm its at its maximum length giving a very narrow field of view (only a few degrees) and hence anything seen thru it will look magnified a lot more

you also get other optical effects due to focal lengths, which i`m sure some of the links will show

hope i havent confused you more heh :)
 
Well I have to say that I do now understand what it is all about, I tried to work it out myself but just a tad too complicated so I thought I would ask the people who would know, thank you all very muchly :D

Stu
 
Fireblade2K4 said:
Ok so would I be right in saying that a 70-300mm lens on a Canon would actually give a focal length from 112mm - 480mm?
Click to expand...

Indeed it would, just a touch longer reach than your S3.

Hope that between us all we have managed to clear everything up :)

Kimmett
 
Fireblade2K4 said:
Ok so would I be right in saying that a 70-300mm lens on a Canon would actually give a focal length from 112mm - 480mm?

Stu
Click to expand...

No, the focal length is still 70-300 but because of the smaller sensor (assuming you are not referring to a full frame Canon) the lens will give you a view equivelent to a 112-480mm lens used on a 35mm film camera or a full frame digital.
 
KIMMETT said:
Indeed it would, just a touch longer reach than your S3.

Hope that between us all we have managed to clear everything up :)

Kimmett
Click to expand...
You sure have thanks a lot...will make looking for a d-SLR and lenses now so much easier...thanks again all.

Stu
 
fireblade mate, do you have msn? I know quite a lot about cameras, and would love to talk 'Deo with you too :)

Tom.
 
You must log in or register to reply here.
Back
Top Bottom