Canon EF-S 17-55mm VS Sigma 17-50mm VS Tamron 17-50mm?

Sovern wrote:

jitteringjr wrote:

You need to do more homework on perspective. Here read this:

http://www.josephjamesphotography.com/equivalence/#perspective

"Perspective is a function only of the distance of the camera from the subject"

So you point to some random photographers website as a reference? How come when I mount my 85mm 1.8 on my 450 and a 5D the perspective does not change? Can you explain that to me? I get the same compression just sides of the frame are chopped off on the 450D if I'm shooting at the location so I have to back up which leaves me with less bokeh or less capable bokeh.

The only thing that changes is the field of view between the different size formats which makes you either move forward or move backward if you want to get the same scene as one format.

A 50mm is going to be a 50mm on a crop body or not, the only thing that changes is field of view hence why people say 50mm on 1.6X body (or 80mm FOV).

A 50mm lens on a crop body will not magically give you the perspective (which means features such as compression) as an 80mm lens it only changes the field of view of which you see. You will have less field of view on the crop body forcing you to back up to get the same shot as you would on a FF body.

Joeseph James aka posting now under Great Bustard is not random and is an authority on this.  The same 'prime' lens on crop and full frame can't give equivalent images.  If you stand in the same placeswitch the same lens, then perspective will not change because the camera didn't move.  However the cropped image will be just a cropped version of the FF.  So say you try to move the crop camera back with the same prime lens to frame the same image.  Well then you moved the camera relative to the subject and ask have said three times now, you just changed the perspective of the subject.  So your image is not equivalent.  So to get equivalent images, you need to be standing in the same location relative to the subject and use a focal length 1.6 times longer on FF.  I'm not going into aperture yet until this part is understood.