this post was submitted on 30 Nov 2023
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Understanding relative focal length with crop sensors (alien.top)
submitted 9 months ago by [email protected] to c/[email protected]
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Hi all,

I'm trying to better understand relative focal length. I shoot with a Nikon D500 (APS-C) and up until now have done mostly sports photography. I'm trying to get more into street photography but trying to understand what I'll be shooting with based on the lenses that I currently own and I'm a little confused. Can you please confirm if my thinking here is correct.

Here are the lenses I currently own and (my assumption about the relative focal length with this crop sensor camera):

  • Nikon AF-S 70-200mm f/2.8E FL ED VR (105-300mm)
  • Nikon AF-S 50mm f/1.8G (75mm)
  • Nikon AF-S 35mm f/1.8G DX (35mm since it's a "DX" lens)

Are my assumptions correct? If so, do I not have a true 50mm focal length lens for this camera body? I was looking to shoot with a 50mm to start out my street photography journey.

Thank you for the help.

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[–] [email protected] 1 points 9 months ago

Here is the basic equation explaining the relationship:

Focal length / Sensor width = Distance to subject / Width of field at subject

A normal lens for a camera is defined as one whose focal length equals (more or less) the width of the sensor. Often, the width of a sensor is measured from opposite corners. A focal length equal to the sensor width will give you a width of field—at the subject—equal to the distance to the subject. Doubling the focal length halves the width of view, doubling the sensor width doubles the width of view, etc.