# Thread: The relationship between focal length, focal distance and aperture?

1. ## The relationship between focal length, focal distance and aperture?

If i use a 50mm f1.4 for a subject that is 5metres away, is the result the same as using a 100mm f2.8 for the subject at 10metres away?

2. ## Re: The relationship between focal length, focal distance and aperture?

With a circle of confusion of 0.03mm, the DOF with 50mm f/1.4 @ 5m is 4.61-5.46m. With 100mm f/2.8 @10m the DOF is 9.23-10.9m assuming the same circle of confusion size. You can use the DOF chart or online DOF calculator to find the DOF limits. Here is one such website:

http://www.dofmaster.com/dofjs.html

Cheers.

3. ## Re: The relationship between focal length, focal distance and aperture?

Originally Posted by ziploc

With a circle of confusion of 0.03mm, the DOF with 50mm f/1.4 @ 5m is 4.61-5.46m. With 100mm f/2.8 @10m the DOF is 9.23-10.9m assuming the same circle of confusion size. You can use the DOF chart or online DOF calculator to find the DOF limits. Here is one such website:

http://www.dofmaster.com/dofjs.html

Cheers.
can also add the difference in perspective..scene/subject/background will look different because the distance is different..the farther you are the flatter the perspective becomes

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