Originally posted by audiobomber Calling it an FA 77 f1.8 is always correct. What causes a backlash is when someone calls it a 115mm f1.8 FF equivalent. You can call it a 115mm f2.7 equivalent when it is mounted on an APS-C body, but you can't mix equivalent focal length without also converting aperture.
To be honest, I think this terminology (in bold) should also be scrapped. It is (apparently) confusing from an exposure sense and people will
always complain about it, no matter how careful you are in explaining what you mean by the f2.7 equivalence. There's something ingrained about f-stops that I don't think you can beat out of people without using a very large textbook.
I think the best bet might be to confuse people with more numbers so they don't even know what to ask, start including the iris diameter in mm (and inches), pupil magnification (this would be nice in any case), the fields of view in degrees for width, height, and diagonal (also include a radian conversion) for the body it's intended for, and also throw in the standard binocular version of field of view (how wide in ft the image is at 1,000 yards, also convert to metric).
Originally posted by audiobomber Mixed equivalence is what some manufacturers use to advertise their products, especially bridge cams. A Sony RX10 has an 8.8-73.3mm f2.8 lens. It is 24-200mm f7.6 equivalent lens. It is definitely not a 24-200mm f2.8, which would be a huge and expensive lens.
We had someone flogging the superzoom nikon p900 as having a 24-2000mm, f2.8-6.5 lens. Despite direct questions about the actual focal length of the lens, he kept claiming it really was a 2000mm/f6.5 lens. Awesome how they managed to defy physics.
---------- Post added 07-22-15 at 11:20 AM ----------
Originally posted by Parallax Actually, the easiest way is for a person to to learn how each of his/her lenses render on his/her camera(s), regardless of sensor size, and think of "equivalence" as just another word in the dictionary.
Many aps-c users ask about what happens to their lenses if they get a FF camera. For pentax folks, I've often suggested they pick up a cheapo k1000 or other k-mount film camera. A practical hands on demo can go a long way.