The purple corner effect is fixable using Photoshop tweaks or programs like Cornerfix. Effective use of either requires calibration images. In lenses that exhibit moderate to strong purple corners on the NEX-7, apertures wider that about f/5.6 require their own calibration images.
That’s a lot of calibration images to keep track of. One for each lens at f/5.6 or f/8, and one for each lens at f/4, and f/2.8, and f/2, and so on until you reach the maximum opening for each lens. If you’re a real perfectionist, maybe you’ll do images at half or third stops. The worst part is figuring which calibration image to use. You can probably remember, and add to the keyword list before you forget it, which lens you used. But can you remember the aperture? The NEX-7 will help you with neither datum; once you put a non-Sony lens on the camera, it doesn’t know what kind on lens it is, or what aperture it’s set al.
Writing down the aperture of every shot in a notebook is a pain. What else can the NEX-7 user do? A few ways to cope:
- Carry an erasable slate. Write the lens ID and f-stop on it whenever you change either. Take a picture of the slate.
- Live with the purple corners. Consider them a camera fingerprint and celebrate them in the same way that some photographers do the edges of Polaroid 55P/N negatives. This is my least favorite option.
- When you get a keeper, run Cornerfix against it with profiles for all the apertures of that lens. Pick the right one by eye.
- Use only lenses that don’t shade the corners much. The Leica 50mm f/1.4 Summilux is a great lens, and has only mildly magenta corners at f/5.6 or smaller apertures. Anything longer should be fine.
- As a special case of the above, don’t use wide angle M-mount lenses; use SLR WA lenses instead. Their greater flange distance (to stay out of the way of the swinging mirror) makes them less susceptible to purple corners. These lenses are usually bigger and heavier, though, and changing the apertures on G-series Nikkors is a problem. One exceptionally small and light (and sharp) SLR WA (though it’s not a WA on the NEX-7) is the Nikon 35mm f/2 D.
- Make only black and white images with lenses that have offensively purple corners.
- Don’t use apertures wider than f/5.6, so you only have to calibrate the lens at one f-stop. Most WA lenses aren’t their sharpest at f/8 and smaller (numerically larger), so that plan could limit you to one aperture setting.
- Get an NEX-5 or 5n; they don’t have the problem to a great degree.