kenerickson
TPF Noob!
- Joined
- Jul 19, 2012
- Messages
- 62
- Reaction score
- 9
- Location
- Waupaca Wi
- Can others edit my Photos
- Photos OK to edit
Please forgive me if this has been asked before.
I am trying to understand focal length as it pertains to DSLR, specifically a Sony A77 (crop sensor) and a Tamron 150-600mm zoom lens. My understanding of focal length is the distance from the point of convergence or optical center to the sensor measured in mm. My 150-600 when zoomed out to 600mm mounted and with me guessing the location of the sensor in only about 15 1/2 inches from the extreme front of the lens to the sensor. 600mm converted to inches = 23.6 inches. My question is how is the 600 mm derived for this lens when it does not physically come close to the 600mm?
I am trying to understand focal length as it pertains to DSLR, specifically a Sony A77 (crop sensor) and a Tamron 150-600mm zoom lens. My understanding of focal length is the distance from the point of convergence or optical center to the sensor measured in mm. My 150-600 when zoomed out to 600mm mounted and with me guessing the location of the sensor in only about 15 1/2 inches from the extreme front of the lens to the sensor. 600mm converted to inches = 23.6 inches. My question is how is the 600 mm derived for this lens when it does not physically come close to the 600mm?