Is focal length internal or external?
49187
What is focal length and how does it affect my photos?
33676
Internal and external forces
104610
What focal length lens do I need for photographing the moon?
91299
What does a megapixel designation on a lens actually mean?
146325
How is zoom measured?
85837
What's the difference between real and effective aperture?
1032
What is the reference point that the focal length of a lens is calculated from?
57844
What lens focal length most closely resembles the perspective of the human eye?
12994
Is it physically possible to build a long zoom (17-300 mm for example) at an aperture value of around 1.4 or 1.2?
34583
How can I calculate sensor size (width and height) from focus length, vertical, and horizontal angle of view?
20439
Do lenses have focal planes or focal spheres/ellipsoids?
107818
What is the shape of the focal plane?
134974
What is the focal length on your typical cell phone camera?
94271
What is the reference plane used when the minimum focus distance is measured?
53448
Do bigger focal lengths capture more light?
8552
Which focal-length lens is usually used for portrait photography, and why?
148416
What do the different Canon DSLR image size settings mean?