Stupid Crop Factor Question

SkipD wrote in post #11752183
First off, you don't have to multiply ANY focal length used on your camera by 1.6.

Sure he has to. Everywhere where he needs to know the focus length, whether to evaluate potential motion blur or let's say compare the field of view with other setups he must multiply.

Refresh Image wrote in post #11755879
Sure he has to. Everywhere where he needs to know the focus length, whether to evaluate potential motion blur or let's say compare the field of view with other setups he must multiply.

Baloney.....

All one needs to do to determine the focal length of the lens on his/her SLR camera is to look at the lens. If the lens is a fixed focal length, look at the ring around the front element. If the lens is a zoom lens, look at the scale coupled with the zoom ring.

The "crop factor" calculation for "35mm equivalent focal length" has only one valid use. That is for comparing the field of view of lenses used on two different format cameras.

Here's one common example: Joe took a photo of Mount Rushmore with a 35mm camera from a particular place using a 200mm lens. You want to replicate that photo with your Canon 7D. What focal length do you need to do that from the same location that he took his photo? Divide the 200mm by 1.6 and you get the answer - 125mm.

Here's another popular example: Mary Sue has been using a Canon SX120 IS point-n-shoot camera and is wanting to use a Canon 50D DSLR. She is, of course, interested in what focal lengths she would need to keep the versatility of the SX120 camera's 10X super-zoom lens. The SX120 lens is actually a 6.0mm to 60.0mm lens, but the advertising also shows the "35mm equivalent" focal length range as 36mm to 360mm. To know the focal lengths needed for the 50D, merely divide the "35mm equivalent" values by 1.6. In other words, Mary Sue would need 22.5mm on the short end and 225mm on the long end for the 50D to have the same field (angle) of view coverage as her SX120 IS camera.

The "crop factor" is NOTHING MORE than a REFERENCE between the two camera formats that lets you compare the field of view of particular focal lengths between the two formats.

The "crop factor" (as related to using lenses essentially designed for 35mm SLR cameras) is always given assuming that the 35mm format (24mm X 36mm) is the reference master. Something to realize, though, is that the 35mm film format is not, never has been, and never will be the "master" format against which all other camera formats are referenced. It is simply the format of the cameras that have also evolved into today's commonly used digital SLRs.

Right. I think I'm getting this. If I want to use a "normal" lens on my FF I use the 50mm. If I use the 50mm on my XSi it's still a fifty but it's no longer a "normal" lens. If I want a "normal" on my XSi I use a 28mm, roughly. Am I in the ballpark here?

R1200GS wrote in post #11756078
Right. I think I'm getting this. If I want to use a "normal" lens on my FF I use the 50mm. If I use the 50mm on my XSi it's still a fifty but it's no longer a "normal" lens. If I want a "normal" on my XSi I use a 28mm, roughly. Am I in the ballpark here?

Precisely...