Infinity

[snapper78]

How far away is infinity in actual practice? As far as I can tell nearly all if not all my lenses reach the infinity stop at less than 50 metres. Does this mean that objects further away than say 50 metres are acceptably sharp or could they be sharper if the infinity stop was set differently? Did photo reconnaissance planes in WW2 have lenses that were optimised for distances of thousands of feet?

 

[Ambro51]

once a lenses hyperfocal setting encompasses “infinity”, relating to circle of confusion, you cannot get any ‘sharper’.

 

[David Hughes]

Far away enough for light to come from the subject in parallel rays.

In practice I can't see infinity ever being needed as things on the earth and around us in our solar system are nowhere at infinity. And outside the galaxy there's always something further away...

Regards, David

 

[OlivierAOP]

From thin lens formula: 1/Dim + 1/Dobj = 1/f where Dim is distance from lens to image, Dobj is distance from lens to object, f is focal length.

Say f=50mm, Dobj=50m=50 000mm. Then Dim= 50.05mm which is 0.05mm from infinity position, likely well within the DOF.

For a real "thick" lens it's similar but distances are measured from the principal points.

 

[snapper78]

Thanks people. Practical tests seem the way forward in determining how to get max depth of field on 135mm lenses used on a mirrorless camera (Lumix G1). Wrong focus and camera movement are fairly easy to tell apart. Naturally one should use a tripod but...