Ask Matthew
Our Nikon savant Matthew answers all your questions
Q
I’m a bit confused about the ‘bokeh fringing’ that was mentioned in issue 105’s Big Test of portrait lenses. What does it look like in actual images?
Jim Monger
A
When people talk about colour fringing, they’re usually referring to lateral chromatic aberration. This shows up mostly towards the edges and corners of the image frame around highcontrast transitions, for example dark branches and leaves on trees against a bright sky. Longitudinal chromatic aberration, also called ‘axial’ or ‘bokeh’ fringing occurs when a lens fails to focus all colours of the spectrum at the same point in the path along which the light is travelling.
It’s mostly a problem when using ‘fast’ lenses that have a wide aperture rating. It can occur across the entire image frame, noticeable as fringes of different colours around high-contrast transitions in a scene that are either in front of or behind the point of focus. The fringing can be red, green, blue or a combination of all three. It’s typically much reduced if you narrow the aperture a little.
Q
I accidentally nudged the VR switch on my 24-120mm lens to ‘Active’ instead of ‘Normal’ but it didn’t seem to make any difference to the results. When should I use each option?
Des Gardner
A
The Normal mode is recommended for general handheld shooting and includes automatic horizontal panning detection, resulting in correction only being applied for vertical vibration. This is disabled in Active mode, so avoid it when panning. Active mode is designed to compensate for more extreme vibrations with different frequency characteristics than normal handheld shooting, for example when you’re shooting from an unstable platform or a moving vehicle.
Some telephoto VR lenses have auto tripod-detection, or a switchable Tripod mode. In most cases, however, it’s best to switch VR off when using a tripod. When using a telephoto lens on a monopod, Nikon recommends Active VR for static shots and I’d use Normal VR when panning. Some recent lenses have a Sport mode instead of an Active mode. This aims to keep the viewfinder image as stable as possible, making it easier to track erratically moving objects – like animals, for example.
Q
My 14-year-old granddaughter is showing an interest in photography. Would you recommend I buy her a D5600 kit or a secondhand body with my 50mm lens that I rarely use?
Graham Husbands
A
I’d go with the D5600 kit that comes with the AF-P DX 18-55mm f/3.5-5.6g VR zoom lens. It’s a compact yet sophisticated camera that’s easy to get started with. It’s also more able
than the D3500 to keep pace with budding photographers, as they continue to learn new skills and techniques. The articulated rear touchscreen is another great bonus.
I think the 50mm prime lens that you have might be a bit limiting for general shooting with any DX format camera, as the 75mm effective focal length will often be a bit on the long side. It would work well on a full-frame body, so you could consider a used D600 or D610, which start at around £425. Even so, the D5600 kit with its retracting zoom lens is more compact, easy to carry around and get to grips with.
Q
I’ve been told to always use UV filters on all of my lenses. However, I removed one on my last shoot and the images seem sharper. What’s your advice?
Ron Bell
A
Practically all modern lenses feature coatings, so the use of a UV filter isn’t necessary from an optical point of view, but many use them for physical protection of the front element. However, if you fit a cap when storing a lens and a hood while shooting, the chances of scratching the front element accidentally are slim. Some recent lenses feature a fluorine coating on the front element, to repel grease and moisture.
High-end protection filters shouldn’t reduce sharpness, but it is possible. A greater problem is that ghosting and flare can become worse when using a filter. It can be especially noticeable with the moon, street lamps and other bright lights in twilight shots and night-time cityscapes. In this situation, I’d remove the filter.