I recently bought a Sony A7 II moving away from Nikon DSLRs (I owned a D800E) and I am using (with adapters) all my other lenses like the M42s, the Nikons of course and the Leica M-mount lenses I have, made by Voigtlander.
One lens that I simply love is the Voigtlander Color Skopar 21/4. It’s just a marvellous, amazing lens. Sharp (maybe even sharper than the Leica equivalents), great colour rendition, amazing black and white. I have been using it on my Bessa R3A for years now.
I thought I’d share my experience of using this lens on a digital mirrorless camera. In my case, Sony A7 II. Here it is mounted on the camera, via a Commlite close-focus Leica M adapter.
It’s pretty known that wide angle lenses on mirrorless cameras are an issue because their back nodal point gets too close to the sensor and this causes weird color shifts on the left and right sides. This happens on Sony, Fuji or even Leica cameras. The phenomenon is called “lens cast”. What camera manufacturers do is to embed correction in the camera firmware, but the lens must be coded and recognized by the camera. This is what Leica does for their lenses. Unfortunately, Sony A7 II does not have this possibility so we need to think of something else.
First though, let’s see what the problem is about.
This is a shot straight off the camera. As you can see, there’s a lot of color shift on the left and right sides - and a substantial vignetting. I shot this at f/4 (full aperture) and underexposed to exaggerate the problem.
I am a Lightroom user so I searched for a solution to this problem. Naturally you can do it manually but it’s a bit tricky to correct the color shifts, really. Photoshop is a lot better for this as you can use masks but Lightroom does not have this possibility.
Fortunately, Adobe have released a Lightroom plugin called “DNG Flat Field”, which is what I needed. Can be downloaded from here.
It works by using a calibration image, it applies this image as a “negative” layer and removes the vignetting and the cast. The calibration image is an image shot in the same aperture condition of the original image but with no details. It can be taken by shooting through some white translucent plastic with the lens set to infinity.
So when you’re out in the field shooting you take some pictures, take a calibration shot, take some more pictures, take another calibration shot, etc. This is what the plugin recognizes as “interleaved” shots and related correction. I also did something different. At home, I shot a white wall with the lens set at all the different apertures and focused at infinity. So I basically built my “external” calibration shots to be used at any time with any shot. Naturally, you need to record the aperture used for a certain shot. This is how you make the plugin apply the “external correction”.
It works like a charm.
This is the result of applying the external correction to the original image.
As a final note, the plugin can work only to correct the color shift and leave vignetting as it is, if it serves a purpose. Here is the original shot with just the color cast removed.