A question I've always wanted to ask

[bobiscuit]

What is the difference between a lens that has focus markings from (for example) 0.25 metres to 2 metres and then infinity.......... And one that has markings from 0.25 metres to 50 metres and then infinity.

I understand that focal length affects this, but then some zoom lenses like Sigma 50-500mm show markings up to 50 metres... But I had a 500mm prime that was marked up to 200 metres. What made the difference there?

 

[Arkady]

Just the manufacturer's preference, i'd think - since all lenses focus seamlessly from their minimum to infinity, it's probably down to what space is available to put markings on.
Long lenses require more movement of the focussing-ring to move the point of focus from min to infinity, whereas wide-angles require less...maybe that also has something to do with it...
Unless I'm bored, I almost never look at the focus distance these days, though it may have interested me when I was 16 and it was all still new and exciting. And when lenses had more information insctibed on them anyway... I mean what new lenses carry an IR-index now? Or DoF scale?

 

[Tobers]

I imagine that a longer lens will have focus markings out further than a shorter/wide angle lens. Why? Because a wide angle lens will hit infinity much closer to you than a longer telephoto lens.

For example, a 20mm lens at f/4 has a hyperfocal distance of 4.35m whereas a 400mm lens at f/4 has a hyperfocal distance of 1,739m. Therefore no need for focus markings further away on the wide angle lens.

Hyperfocal distance is the distance of the nearest object in a scene that is acceptably sharp when the lens is focused on infinity.

Depth of field calculations courtesy of the iPhone PhotoCalc application by the way, and for a 1.3x crop sensor size before anyone asks.

 

[HoppyUK]

I imagine that a longer lens will have focus markings out further than a shorter/wide angle lens. Why? Because a wide angle lens will hit infinity much closer to you than a longer telephoto lens.

For example, a 20mm lens at f/4 has a hyperfocal distance of 4.35m whereas a 400mm lens at f/4 has a hyperfocal distance of 1,739m. Therefore no need for focus markings further away on the wide angle lens.

Hyperfocal distance is the distance of the nearest object in a scene that is acceptably sharp when the lens is focused on infinity.

Depth of field calculations courtesy of the iPhone PhotoCalc application by the way, and for a 1.3x crop sensor size before anyone asks.

The amount of stuff printed on a lens is largely down to how much room there is. Most primes still have a depth of field scale and many lenses still have an IR focusing mark. DoF scales are of limited use with lenses now being used on different format cameras, which have different DoF characteristics.

Hyperfocal distance is not quite what Tobers has said and those numbers don't appear to be accurate (DoF standards vary!). I'm sure he knows that, but taking the example above with a 20mm lens at f/4 on a crop format Canon, a hyperfocal distance of 5.3m would make everything sharp from 2.65m (half the hyperfocal distance) to infinity - that is the hyperfocal range.

Those measurements sound very exact, because they are based on some precise assumptions. However, those assumptions often don't apply and DoF scales are at best a rough guide.