12-12-2011, 12:16 PM
(This post was last modified: 12-12-2011, 12:27 PM by Brightcolours.)
[quote name='Rover' timestamp='1323691912' post='13649']
I'm not sure I understand this... I thought that using lenses on crop makes them perform better because the worst performing edges are removed? The action you described above matches the effect of a TC (optically magnifying the center of the image) accurately but that's not what is happening on a crop body (which is basically the same as taking a full frame image and then cropping it in Photoshop, since the edges are just not recorded), unless you insist on upsampling the image later to the full frame pixel count of the same pixel density.
Or unless it was intended as another "diatribe" against crop cameras, of course. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' /> j/k
[/quote]
Why do you have the idea that cropping via optics is not comparable to cropping via a smaller sensor, or indeed, cropping on the computer? Pretty odd.
Lets just focus on your cropping in photoshop for a minute.
Make a duplicate of an image. Crop to lets say 50% the duplicate.
Now count the lines per image height.
Guess which image has the higher resolution?
About optical cropping (TC). A lens has only a finite ability to resolve. Suppose it has a maximum, even, resolving power of "100" (in some fictive unit). Now, with a 2x TC, we only use the center part of the lens, which would be able to resolve "50".
That "50" will be distributed over the entire image, where before the total "100" was distributed.
Evidently, the image with TC has a lower resolution.
On to "cropping" with a smaller sensor.
Same lens can apparently resolve "100" on, lets say, a FF 135 format sensor format. Now we crop the projected image to half. Only "50" remains.
Now compare the FF image to the cropped image. Guess which one will have a higher resolution?
It does not matter where of how you crop. Whether it is via the sensor, via extra optics, or on a computer after image capture. It will always lead to the same which is less lines per image height resolved.
I'm not sure I understand this... I thought that using lenses on crop makes them perform better because the worst performing edges are removed? The action you described above matches the effect of a TC (optically magnifying the center of the image) accurately but that's not what is happening on a crop body (which is basically the same as taking a full frame image and then cropping it in Photoshop, since the edges are just not recorded), unless you insist on upsampling the image later to the full frame pixel count of the same pixel density.
Or unless it was intended as another "diatribe" against crop cameras, of course. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' /> j/k[/quote]
Why do you have the idea that cropping via optics is not comparable to cropping via a smaller sensor, or indeed, cropping on the computer? Pretty odd.
Lets just focus on your cropping in photoshop for a minute.
Make a duplicate of an image. Crop to lets say 50% the duplicate.
Now count the lines per image height.
Guess which image has the higher resolution?
About optical cropping (TC). A lens has only a finite ability to resolve. Suppose it has a maximum, even, resolving power of "100" (in some fictive unit). Now, with a 2x TC, we only use the center part of the lens, which would be able to resolve "50".
That "50" will be distributed over the entire image, where before the total "100" was distributed.
Evidently, the image with TC has a lower resolution.
On to "cropping" with a smaller sensor.
Same lens can apparently resolve "100" on, lets say, a FF 135 format sensor format. Now we crop the projected image to half. Only "50" remains.
Now compare the FF image to the cropped image. Guess which one will have a higher resolution?
It does not matter where of how you crop. Whether it is via the sensor, via extra optics, or on a computer after image capture. It will always lead to the same which is less lines per image height resolved.