When lens is DX, is f/2.8 value changed?

4 years 2 months ago #675742 by Pat White
I'm confused, I thought that the field of view is changed when FX lens is used on DX camera.  That aperture is unaffected?  I was told today by another photographer that this actually is equivalent to something like f/4.5?

What am I missing here?


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4 years 2 months ago - 4 years 2 months ago #675748 by Shadowfixer1
2.8 is 2.8 no matter what. It's a mathematical representation of the opening. What the person was trying to say, if they knew what they were talking about is 2.8 on a smaller sensor will give more depth of field if the subject is made the same size in the image. Since it's a crop sensor that means you have to increase the distance between the camera and the subject to maintain the same subject size which increases the depth of field. The key change is distance to the subject. Hope that helps you understand.
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4 years 2 months ago #675768 by garyrhook
+1.

It is impossible that changing one physical attribute will change another. A smaller sensor does nothing to the aperture nor the focal length.

What does change is geometry (yes, photography involves math), as explained. 


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4 years 2 months ago #675874 by Pat White
Gotcha, I see and get it now.  Big thanks for the much needed clarity!  

Actually, Gary - when you say the geometry changes, what do you mean? 


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4 years 2 months ago #675878 by Nikon Shooter
To get to the right spot, go to 12:17 m to 13:51 m.
The whole thing is really cool but this will answer
your question:


Light is free… capturing it is not!
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4 years 2 months ago #675980 by garyrhook

Pat White wrote: Gotcha, I see and get it now.  Big thanks for the much needed clarity!  

Actually, Gary - when you say the geometry changes, what do you mean? 


Size of sensor, size of sensor element, distance from camera to subject, from camera to background. And, of course, the area of the aperture and the lens focal length. All geometry.


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