Focusing At Narrow Apertures
Focusing At Narrow Apertures
Nikon, and other DSLR centric brands, do not care about people who prefer to use manual focusing. This is one reason why I abandoned Nikon in 2011-12. After several attempts with three different Nikon cameras I could not achieve reliable results with the green dot method.
Obviously, I am not familiar with all of the new Nikon platform's focusing aids. For all I know, Nikon decided to implement powerful focusing lens aids for non-AF lenses.
In general, I found the best alternative for focusing with narrower apertures is focus peaking. There are two approaches.
- You simply make sure the intended focus point displays intense peaking.
- Move the focus region and temporarily crop (zoom) the EVF display to select the focus point. Then maximized the peaking.
In my case it took a while to learn how to read a display with focus peaking. It is confusing to observe large regions with peaking when DOF is wide. Field curvature can add to the confusion. Regions and objects with more contrast can have more intense peaking than a lower contrast objects that happen to be at the focus point. With wide angle lenses these problems can be disorienting. That's the bad news. The good news is if the intended region or subject displays heavy peaking, it will be reasonably sharp in the rendered image. I realize perceived sharpness is only maximized at the true, but unknown, focus point. The issue is whether or not the MTF50 degrades significantly (the actual lens MTF50 is inferior to the
total systems' MTF50) when changes in peaking are not able to differentiate the intended focus point. It just may not be not practical to optimize focus for non-AF lenses with the tools at hand. This doesn't mean acceptable focus is impossible
The second method attempts to minimize these problems by cropping the display. This usually makes maximizing the peaking intensity more selective. But it is slower unless the camera supports some sort of picture-in-picture display mode. I use a mirrorless camera with an OVF finder than can display a PIP, EVF, zoomed focus region. I primarily use focus peaking but occasionally use a simulated, split-screen display. I use different zoom levels for different circumstances.
There are some other variables that can help with focus peaking. Reducing peaking sensitivity could increase selectivity. Different peaking color options might work better for different people. For raw-file users, experimenting with in-camera JPEG rendering parameters could help too.
Low light reduces the effectiveness of all focusing methods. Similarly, scenes with low native contrast are also a challenge. In very low light EVFs are affected by low S/N.
Focusing wide open is an entirely different matter.
