Unwanted correction 3rd party lenses?
|Modern SLRs can correct lens aberrations such as chromatic aberration, vignetting and distortion. What can be corrected, and what choices the camera user can make, varies by camera brand.
The Nikon D3200 corrects jpg files automatically for chromatic aberration without offering a choice to the camera owner. The Canon 650D corrects also for chromatic aberration in jpg files, but the camera owner must first selsect this option in the camera menu.
Typically, only JPEG files are corrected for lens aberrations and RAW files remain unchanged. But the RAW files from Panasonic cameras are first corrected before the user gets to see his picture in Lightroom or Photoshop.
In order to perform the lens correction properly, the camera must know which lens is used. And that is not as straight forward as you wish!
|Here you see a menu page of the Canon 650D. The camera shows which lens is attached to the camera and that correction data are available for this lens. The Canon user can then choose whether or not to correct jpg files for vignetting and / or chromatic aberration. Sony and Nikon cameras offer basically the same functionality, but the execution is different.
But what happens when you attach alens to the camera, which is not made by the camera manufacturer, but for example by Tokina, Sigma or Tamron? The Sigma 150mm macro and the Sigma 180mm macro, for example, are lenses which exhibit very little vignetting. But if you leave the lens correction of your Canon 5D MK3 left on, then the camera uses a lens correction profile of a Canon 100-400 L (a lens with strong vignetting) to "correct" the jpg files made with a Sigma macro lens.
|How can you recognize unwanted lens correction? When your jpg files show a dark spot in the center, as shown in the image to the right, while the corresponding RAW files do not exhibit this phenomenon, the camera corrected the jpg file for vignetting where it shouldn't.
Unfortunately it is not always true that if the LCD screen indicates that no correction is applied, it actually does not happen. It can be even more complicated! When you attach a Tokina 10-17 mm to a Canon 5D MK2 camera, you will see on the LCD menu that no lens correction data are available. But the Canon 5D MK2 still applies lens correction, even if you have switched lens correction off, for vignetting from the jpg files created with the Tokina 10-17 mm . The camera uses the lens correction profile for a Canon 85 f/1.2 L. That's a completely different type of lens, with very different characteristics from the Tokina fisheye lens.
Roger Cicala from Lens Rentals tested a large number of Tamron, Tokina, Sigma and Zeiss lenses, attached to four different Canon cameras, in order to find out what happens. Read the full article "Canon-illumination-correction-and-third-party-lenses", containing tables with lens correction for Tokina lenses, Sigma lenses and Tamron lenses.