Math camera question, So an FX lens on a DX camera multiplies

[Auslese]

the image by 1.5, thus a 50mm on a Nikon 7100 becomes a 75mm instantly, if then I enable the 1.3 crop mode, does this effectively make the 75mm a 97.5mm, which is actually a short telephoto? Also are the edges cropped twice, or does is the sensor adjusted in some way? The answer to that determines whether the 1.3 crop mode should ever be used, because if it is just cropping the outlines, this can also be accomplished to exact specs in post processing. ???

 

[SCraig]

Neither. The FIELD OF VIEW is decreased by a factor of 1.5. If you put a 100mm lens on a full frame body and a APS-C body the MAGNIFICATION will be the same. The difference is in the field of view only.

If you enable 1.3 crop mode it does exactly as the name implies, it crops the image further.

 

[Designer]

You seem to be off into the weeds with this.

You should not confound the two attributes of focal length and field of view.

The focal length will always stay the same no matter what camera you put it on. The projected image circle will also be the same no matter what camera you put it on.

The difference is that the smaller sensor "sees" only the middle of the projected image circle, whereas the larger sensor is able to "see" more of the projected image circle.

 

[Auslese]

You seem to be off into the weeds with this.

You should not confound the two attributes of focal length and field of view.

The focal length will always stay the same no matter what camera you put it on. The projected image circle will also be the same no matter what camera you put it on.

The difference is that the smaller sensor "sees" only the middle of the projected image circle, whereas the larger sensor is able to "see" more of the projected image circle.

That said, for telephoto shots a DX camera would be better, as you are trying to get larger anyway, and when an image gets to post processing it is typically framed anyway, which is further cutting off of the edges.

 

[snowbear]

Prior to post, the image on a DX is not larger than same scene (all other things being equal) as FX. The scene will be narrower in DX, but not larger.

 

[astroNikon]

This may help some more ==> Camera Sensor Crop Factor and Equivalent Lens Focal Length

But don't get caught by what you computer does to show you an image on the screen too. A lot of software will default an image to full screen.