Lenses are more than just glass in a barrel. The way they bend, scatter and transmit light shapes every photograph we make. From the subtle swirl of a vintage Petzval lens to the clinical sharpness of modern optics, the behaviour of a lens explains why some images feel dreamy while others look razor‑sharp.
To help make sense of this, we’re going to untangle some of the jargon photographers often stumble across when reading lens reviews or technical discussions.
Scheimpflug Principle
The Scheimpflug principle describes how tilting a lens changes the plane of focus. Instead of focusing parallel to the sensor, the focus plane tilts, allowing you to get more (or less) of a subject in sharp detail.
Large format and tilt‑shift lenses use this principle to keep both foreground and background objects in focus, or to create dramatic selective focus effects.
Hyperfocal Distance
Hyperfocal distance is the focusing point that maximises depth of field. When a lens is focused at this distance, everything from half that distance to infinity appears sharp.
Landscape photographers often use hyperfocal focusing to keep both foreground and distant mountains crisp.
Circle of Confusion
The circle of confusion is a technical way of describing how small a blur spot can be before our eyes perceive it as sharp. It’s central to calculations of depth of field.
In practice, different sensor sizes use different assumptions for the circle of confusion, which is why depth of field calculators often ask what camera you’re using.
Download the iCAMERA eBook
Get a free copy of iCAMERA and we’ll also send you the latest iPhotography news, regular photo articles, and amazing deals straight to your inbox.
Bokeh
Bokeh refers to the aesthetic quality of the out‑of‑focus areas in a photograph. It’s not simply blur, but the look of that blur.
Some lenses create creamy, smooth bokeh, while others show harsher or more patterned backgrounds. Terms like “soap‑bubble bokeh” or “onion‑ring bokeh” describe the shapes that highlights take on.
Modulation Transfer Function (MTF)
MTF charts describe how well a lens can reproduce fine detail and contrast. They show resolution at different points across the image frame.
While charts can feel intimidating, all they reveal is whether a lens stays sharp in the corners or loses detail away from the centre.
Aberrations and Optical Quirks
Lenses are never perfect. Coma causes points of light to stretch like wings near the corners. Chromatic aberration creates colour fringes. Field curvature means focus bends slightly across the frame.
Knowing these quirks helps photographers decide whether to embrace the look or correct it in editing.
Frequently Asked Questions (FAQs)
What’s the difference between bokeh and blur?
Bokeh describes the character of out‑of‑focus areas, not just their softness.
Why do some lenses have onion‑ring bokeh?
It comes from the way aspherical lens elements are polished.
Do MTF charts really matter?
They’re useful for comparisons, but real‑world shooting tells you more about a lens’s character.
Can I calculate hyperfocal distance easily?
Yes — there are apps and charts to do this quickly in the field.
Are optical flaws always bad?
Not at all. Many photographers enjoy the personality that quirks like swirl or flare bring.
Lens behaviour is both science and artistry. Technical terms such as hyperfocal distance, Scheimpflug, and MTF charts may sound intimidating, but once you understand them, they become tools to shape your creative style.