This is an update to the Ricoh GR III review and it’s specifically about vignetting.
If you shoot RAW, Photoshop doesn’t correct vignetting in Ricoh GR III files, but Lightroom has a toggle switch that applies vignetting correction.
Why Vignetting Occurs
Lenses are a compromise. Let’s say a manufacturer wants to make a lens that has the best optical characteristics. What does that mean? It means the lens renders a sharp and accurate image across the whole frame.
Yes, but the sensor is a certain ratio, say 3:2 like a frame of 35mm film, but the image that the lens projects is circular. So part of the light from the lens has to be curved to fit the frame. Now we see how complicated lens manufacture is.
That is why if there is any failure to be sharp across the whole frame, it is almost always the outer corners of the image that are not as sharp. The centre is usually the sharpest part of the image.
So how else can it go wrong? It depends on the focal length of the lens. Some lenses have a tendency to bulge the image in the middle, with what is called barrel distortion. What should be straight lines bend outwards. Less common, is pincushion distortion, which is where the lines bend towards the centre.
Other lenses simply don’t project as much light into the corners of the frame, so the outer edges are darker, with what is called vignetting.
Here is a representation of barrel distortion.
How Manufacturers Hide Barrel Distortion
In the days of film, manufacturers either solved the problem of barrel distortion in the process of making the lens or they didn’t. If they didn”t then there was no cure.
Digital camera manufacturers can take a different approach. Make the best lens you can, and then hide its failings with software before the image is sent to the card.
The problem with using software to hide barrel distortion and make straight lines straight, is that it affects the sharpness in the corners. And that’s no wonder, given that the shape of the image is being ‘stretched’ by digital manipulation..
This is the reason that top quality lenses are expensive. Manufacturers like Nikon spend a lot on lens research. They use materials and coatings that correct the image at source – in the lens. They work with fine manufacturing tolerances that means the lenses work as they are supposed to. They don’t have to use software to hide the faults.
The Ricoh GR III
The GR III is a tiny camera with a 28mm wide angle lens. That physical design doesn’t leave much room for a perfect lens design.
The biggest failing of the camera is vignetting. The middle of the image is bright and well lit and the outer edges are dark. If you shoot JPEG then you wouldn’t know it. That’s because the software in the camera ‘corrects’ or hides the faults.
But if you shoot RAW, Photoshop doesn’t correct the vignetting. It is kind of possible to correct it by increasing the brightness of the shadows and darkening down the highlights, but it’s hit and miss.
There is a solution, and I discovered it a day or two ago. Use Lightroom. It has a specific correction for the vignetting of the Ricoh GR III.
Actually, I heard about this a little while ago, but I don’t use Lightroom very much, and it took me a couple of times of being told before I opened the application..
Here are two version of a photo processed in Lightroom. In the first photo you can see how the path in the lower right part of the frame and the trees to the left and right, are darker.
In the second photo of the cows I used the lens profile correction in Lightroom, and you can see that the shadows caused by insufficient light reaching the corners, is no longer there. The image is bright all across the frame.
Finally, below the two photos of the cows is a screen capture of the Develop module in Lightroom, with the lens profile correction on. Look over at the right hand panel and the section for Lens corrections and you can see the the profile corrections is ticked. I didn’t input in the camera make and model – Lightroom found these automatically.
Image Stretching – Something Has To Give
Toggling the profile corrections tab in Lightroom revealed the when it is toggled on, the image stretches slightly. I haven’t tested it with a test card, but I bet that the corners in the ‘software corrected’ version are less sharp than when the vignetting is left uncorrected.