Apeture size

Goldcoin79

TPF Noob!
Joined
May 23, 2012
Messages
152
Reaction score
2
Location
Uk, Hemel Hempstead
Can others edit my Photos
Photos OK to edit
If I am working out the size of the apeture do I use the actual focal length or the 35mm equivalent value eg for a 50mm focal length with an apeture set at f5 on a camera with a 1.6 crop factor is the calculation 50/5 or 1.6 X 50/5
 

kundalini

Been spending a lot of time on here!
Joined
Jul 18, 2007
Messages
13,607
Reaction score
1,936
Location
State of Confusion
Can others edit my Photos
Photos NOT OK to edit
The focal length of the lens is what's stamped on the barrel. A 50mm lens is a 50mm lens. The difference seen is in the Field of View (FoV), not the focal length.

Aperture has no bearing. Use the appropriate aperture for your shot / vision of the scene.
 

KmH

In memoriam
Supporting Member
Joined
Apr 9, 2009
Messages
41,401
Reaction score
5,706
Location
Iowa
Website
kharrodphotography.blogspot.com
Can others edit my Photos
Photos OK to edit
Use the actual focal length.

When you see the term f/4, the f = the focal length of the lens.

So a 50 mm lens, or zoom lens set to 50 mm, set to f/4 has a 12.5 mm diameter lens aperture (50 mm / 4 = 12.5 mm).
A 35 mm lens, or zoom lens set to 35 mm, set to f/4 has a 8.75 mm diameter lens aperture.

When considering Depth-Of-Field (DoF), then the image sensor crop factor does have a bearing, and online DoF calculators make you specify the crop factor in some way. Many just have you select the camera make/model you use.
Understanding Depth of Field in Photography
 
OP
G

Goldcoin79

TPF Noob!
Joined
May 23, 2012
Messages
152
Reaction score
2
Location
Uk, Hemel Hempstead
Can others edit my Photos
Photos OK to edit
Thanks KmH that is the answer I was looking for. When you are talking about the dof calculator are you saying that they calculate the dof by using the crop factor to first calculate the 35mm equivelant?
 

Helen B

TPF Noob!
Joined
Sep 16, 2007
Messages
3,296
Reaction score
467
Location
Hell's Kitchen, New York
Can others edit my Photos
Photos NOT OK to edit
No. With most calculators you use the actual focal length of the lens (and the marked aperture) and specify the format separately.

If you are doing a DoF comparison between formats for similar fields of view and distance then you can use the crop factor on both the focal length and the f-number. For example if the crop factor is 2, a 25 mm lens at f/2 on the crop camera is equivalent in FoV and DoF to a 50 mm lens at f/4 on a full frame 35 mm camera.
 
Last edited:

Most reactions

Top