FOCAL LENGTH.

candyceryj

TPF Noob!
Joined
Sep 5, 2012
Messages
8
Reaction score
0
Hello People,

I'm new to photography. I had been reading some post from blogs and certain websites from professional photographers.
They will always caption for example 100mm 2.8A/F Macro.
I googled and they mentioned it was the focal length, and the types of lens.

So I'm curious what lens the higher the focal length meant? or the lower the focal length meant?
100mm represents the distance it can shoot or?

Thanks for all your advice given! :blushing::blushing:
 

Dao

No longer a newbie, moving up!
Joined
Mar 24, 2008
Messages
6,426
Reaction score
462
Location
St. Louis
In simple optics, focal length is the distance of a in focus image from the optics. So shorter focal length means the in focus image is closer to the optics (lights bend more) than a optical system which has a longer focal length.


In photography, the focal length pretty much related to the "Field of View" or "Angle of View". So a shorter focal length will result in a wider view while a longer focal length will result in a narrower view.

For instance, using a 28mm lens, you see a big tree in the middle of the frame and 20 deers around the tree. But using a 500mm lens, all you see is part of the tree trunk when you pointing to the same spot, deers are not in the frame anymore. So you may say longer focal length give you a higher magnification also.
 

SCraig

Been spending a lot of time on here!
Joined
Nov 12, 2011
Messages
6,474
Reaction score
2,450
Location
Nashville, TN
Website
sc-photo-tn.com
Can others edit my Photos
Photos NOT OK to edit
With a full-frame camera a 50mm lens is roughly equivalent in field of view to the human eye, or in other words it isn't wide angle or telephoto, it's "Normal". On a crop-sensor camera that drops to about 35mm. Anything with a focal length less than that (24mm, 18mm, 10mm, etc.) is considered to be wide angle whereas anything with a focal length higher than that (100mm, 200mm, 300mm, etc.) is considered to be telephoto.

As focal length increases field of view decreases, just like a telescope. Distant objects will appear to be closer however the width of the field of view will be less.

As focal length decreases the opposite occurs. Close objects will appear to be farther off however the width of the field of view increases.
 

sandrat

TPF Noob!
Joined
Aug 15, 2012
Messages
78
Reaction score
3
Location
ABQ NM
Can others edit my Photos
Photos OK to edit
On a crop sensor camera the 50mm lens must be multiplied by 1.6 canon or 1.5 Nikon to get effective focal length. 50mm on canon is 80mm approaching tele photo.
 

Mach0

TPF Supporters
Supporting Member
Joined
Oct 16, 2011
Messages
2,616
Reaction score
432
Location
203
Can others edit my Photos
Photos OK to edit
On a crop sensor camera the 50mm lens must be multiplied by 1.6 canon or 1.5 Nikon to get effective focal length. 50mm on canon is 80mm approaching tele photo.

Effective field of view. The focal length never changes.

An easy way to explain is that a crop sensor crops the image to xyz mm and take the crop factor and do the actual calculation.



The best thing IMHO about crop sensors is that the frame is cropped compared to a full frame and it keeps full resolution. That can come in handy for certain types of shooting.
 

Dao

No longer a newbie, moving up!
Joined
Mar 24, 2008
Messages
6,426
Reaction score
462
Location
St. Louis
Yes, focal length is the optical property of the lens, it has nothing to do with the camera.

Image quoted from Nikon USA (Source)

focal-length-graphic.jpg


The focal length is the "Image Distance" from the above diagram. As you can see, change the recording medium size has nothing to do with the focal length. However, Field of View or Angle of View change with the size of the recording medium. If the recording medium is smaller, the camera may only capture the green part of the tree from the above diagram.


For a photographer who never shoot with other format, it really does not matter much. I really don't care my 7D is 1.6x of the 35mm film or X of medium format or Y of larger format film. All I care is what I see thru the viewfinder whether it is wide enough or narrow enough.
 

table1349

Been spending a lot of time on here!
Joined
Sep 9, 2006
Messages
0
Reaction score
2,772
On a crop sensor camera the 50mm lens must be multiplied by 1.6 canon or 1.5 Nikon to get effective focal length. 50mm on canon is 80mm approaching tele photo.

Focal length is focal length is focal length. It doesn't change. You are talking about field of view, not focal length.
 

sandrat

TPF Noob!
Joined
Aug 15, 2012
Messages
78
Reaction score
3
Location
ABQ NM
Can others edit my Photos
Photos OK to edit
Thanks for the correction...yes field of view.

The other nice thing about a crop sensor is that it will use the often sweeter center of the lens avoiding some of the potential Len's edge issues.
 

Ballistics

Been spending a lot of time on here!
Joined
Jun 5, 2011
Messages
3,781
Reaction score
633
Thanks for the correction...yes field of view.

The other nice thing about a crop sensor is that it will use the often sweeter center of the lens avoiding some of the potential Len's edge issues.

That's because the outside is being 'cropped' out. Hence the term crop sensor.

Canon-5D-VS-Canon-20D-Full-Frame-Versus-Cropped-Sensor.jpg
 

Most reactions

ClickASnap

New Topics

Top