Ricoh GR III Vignetting

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.

an illustration 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.

the develop module in lightroom with lens profile corrections turned on

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.

Coming Off Auto With Your Camera

Let’s start with asking what is a properly exposed photo? And we might reply that it is not too dark and not too light, it’s the Goldilocks photo.

But what about a photo of a street at night with one shop with its lights still on? Now we want or expect most of the photo to be dark, maybe almost black. Or what about a snow scene with a lone tree? Now we want or expect most of the photo to be almost white.

One of the great things about digital cameras is that if you take a photo and the exposure is wrong, you can see that when you review the photo in the LCD in the back of the camera. Then you can adjust your settings and take another photo.

But that’s a bit clunky and it assumes that you are photographing the kind of subject that is going to still be available the next time you press the shutter.

Most of the time the camera gets it right. And you might ask how it does that. How does the camera decide how to expose what it is being pointed at? How does the camera know what it is being pointed at? It could be pointed at a scene with a full range of tones, or it could be pointed at a black cat on a white sheet.

Well, cameras are computers and they analyse the tones in the scene and compare them with a mid-grey reference colour. So if they see that the scene is mostly white, they bump up the exposure to make the photo whiter than mid grey.

So then you can leave your camera on automatic mode and let it make all the decisions.

The end.

Except, as a photographer, you have preferences. You may want more depth of field so everything from near to far is in focus. Or less depth of field to separate the subject from the background. Or a faster shutter speed to freeze the action, or a slower shutter speed to give the impression of movement. And maybe you want the scene to look a bit darker and more moody simply because that’s your style and you are the photographer.

And you can’t do that using the camera’s automatic mode, because the camera makes the decisions, not you.

To exercise more control, you need to use the tools that are at your disposal in the camera , which allow you to control the aperture of the lens, the shutter speed, and the ISO. If those controls still aren’t giving you what you want, you also have access to the exposure compensation dial.

Remember, the camera calculates the amount of light that the camera needs to properly expose the scene. And it has two variables to work with, which are aperture and shutter speed. It is like a simple multiplication table where 2×12 gives the same result as 6×4 or 3×8.

So halving the shutter speed and doubling the aperture will give expose the scene exactly the same a doubling the shutter speed and halving the aperture.

That is because f2 is one stop (twice as much light gets in) compared to f2.8 and 1./200 of a second let’s in half as much light as 1/100 second.

As I explained in an earlier article, imagine if the blades on a lens opened and closed continuously with no intervals to indicate the apertures, then photographers would have no indication of how much more open or closed a lens was as they turned the ring around the lens.

From the early days of photography, lens makers designed lenses with intervals, or stops. As you turn the ring, the blades open one click at a time. And each click opens or closes the aperture by a specific amount. Some lenses have clicks for every full ‘stop’. That means that if the lens is stopped down one stop, then exactly half as much light will reach the film or sensor.

This is very handy for adjusting the shutter speed and the aperture to keep the same exposure because you can double the shutter speed and halve the aperture. Or halve the shutter speed and double the aperture. And so on.

So for example, a shutter speed of 1/100 second and an aperture of f2.8 will give the same exposure as a shutter speed of 1/200 second and and aperture of f2.

Aperture Priority and Shutter Priority

The two most commonly used modes are Aperture Priority and Shutter Priority.

In Aperture Priority, you set the aperture by turning a ring on the lens or a dial on the camera body. That is your variable. You set it.

Once you set your aperture, the camera calculates the correct exposure for that aperture and sets the appropriate shutter speed. That’s all there is to it.

In Aperture Priority you set the aperture and the camera sets the shutter speed.

What you see from this is that you control the aperture but you don’t control the shutter speed. The camera controls that after it has worked out the correct exposure.

But let’s suppose you are photographing a horse race. You are standing right by the track with the horses racing towards you. For that kind of event, you want to be in charge of the shutter speed so you can freeze the action. So you would shoot in Shutter Priority. You set the speed to, for example, 1/1000 second and that is your variable. The camera will calculate the exposure and the camera will set the appropriate aperture. That’s all there is to it.

In Shutter Priority you set the shutter speed and the camera sets the aperture.

I mentioned ISO and exposure compensation. I’ll talk about these in the next articles in the series.