F/stop vs. F/stop issue quizz?

Joined
Apr 5, 2005
Messages
909
Location
Fayetteville, TN
OK, let's see how sharp this group is. This should be easy.

1. Given two lenses with the same focal length, will an F/6.4 have the same depth of field as an F/2.8 when the F/2.8 is "stopped down to 6.4?

2. What part does the diameter of the lens play?
 
Joined
Jan 25, 2005
Messages
994
Location
Alabama
Greg Giesing said:
OK, let's see how sharp this group is. This should be easy.

1. Given two lenses with the same focal length, will an F/6.4 have the same depth of field as an F/2.8 when the F/2.8 is "stopped down to 6.4?

2. What part does the diameter of the lens play?
Greg,

I a noob, so I'll probably get these totally wrong, but I'm going to play anyway. :lol: What better way to learn than to flunk a test or two. 8)

1. They should be the same.

2. None.

Well?

Frank
 
Joined
Mar 18, 2005
Messages
122
Location
San Francisco
Here's my guess.

1.) They are the same.

2.) It will allow faster and more accurate focusing in low light conditions.

Dave
 
Joined
Jan 25, 2005
Messages
994
Location
Alabama
dkapp said:
Here's my guess.

1.) They are the same.

2.) It will allow faster and more accurate focusing in low light conditions.

Dave
I agree with Dave on #2. My answer was based strickly on how the lens diameter affects DOF. 8)

Frank
 
Joined
Feb 20, 2005
Messages
1,089
Location
Leeds, West Yorkshire, England
Flew said:
I a noob, so I'll probably get these totally wrong, but I'm going to play anyway. :lol: What better way to learn than to flunk a test or two. 8)
I think that is the perfect attitude and so in the same spirit I'm going to hazard two guesses...

1 - I'm guessing this is to do with efficiency and tolerances with one lens at its limit and the other with capacity to spare. So I think the DOF will be the same but the stopped down lens will render the entire image sharper and will therefore appear to have the greater DOF.

2- I think this is something to do with the efficiency of light "collection" and so would go with a guess that the larger the diameter the better the lens.
 
N

nfoto

Guest
Greg Giesing said:
OK, let's see how sharp this group is. This should be easy.

1. Given two lenses with the same focal length, will an F/6.4 have the same depth of field as an F/2.8 when the F/2.8 is "stopped down to 6.4?

2. What part does the diameter of the lens play?
1. DOF is identical (I presume both lenses are focused at the same subject at the identical distance)

2. None. The f/number (N) is defined as the diameter of the entrance pupil divided into the focal length. The entrance pupil may exceed the physical lens diameter.
 
Joined
Jan 26, 2005
Messages
1,011
Location
San Jose, CA
Greg Giesing said:
1. Given two lenses with the same focal length, will an F/6.4 have the same depth of field as an F/2.8 when the F/2.8 is "stopped down to 6.4?

2. What part does the diameter of the lens play?
This DOF calculator answers both question.

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

The only input data it requires is distance to subject, focal length of lens, and aperture used.

I like Clive's comment, too. I'd also speculate that two lenses at the same aperture/focal length might yield results that suggest different DOFs because of the varying natures of their bokeh.
 
Links on this page may be to our affiliates. Sales through affiliate links may benefit this site.
Nikon Cafe is a fan site and not associated with Nikon Corporation.
Forum post reactions by Twemoji: https://github.com/twitter/twemoji
Copyright © 2005-2019 Amin Forums, LLC
Top Bottom