Where is infinity?

Started Feb 28, 2013 | Questions thread
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EinsteinsGhost Forum Pro • Posts: 11,977
Re: Where is infinity? measure it.

OldClicker wrote:

EinsteinsGhost wrote:

OldClicker wrote:

" Generally when speaking of infinity focus on a lense one means the lense is set to focus at its hyperfocal distance."

Are sure about that? You cannot focus past the assumed 'hyperfocal distance'?

Actually, hyper focal distance is the minimum distance to focus at, to achieve a DoF that extends to infinity (and half the distance to the point in focus). So, if you have hyper focal distance for a setting of 10 ft, you can focus at 10 ft, or 20 ft. The difference will be that in the former (10 ft) the DoF will extend from 5 ft in front of you to infinity whereas in the latter, it will be from 10 ft in front to infinity.

I don't understand what you mean by the "hyper focal distance for a setting of 10 ft". The lens/aperture has a minimum distance at which the DOF goes to infinity (noting that DOF is a function of many things and not a hard number, but anyway...). That is the HD, correct? It is one distance. If there were a hard stop at this HD (which is what this thread is about), you could not focus beyond that, correct?

Depth of field is dependent on focal length (equivalent), aperture size and distance to focus. Hyper Focal Distance (“HFD”) is the minimum distance to focus to achieve an infinite DoF. Half the distance from that point towards the camera will also be in that DoF (the remaining half won’t be).

Consider these for example:

Camera: Sony A580

Lens: Sony 24mm f/2.8 (at f/4)

Focusing Distance: 1m

For the above setting, the Depth of Field is about 0.28m. The Hyper Focal Distance: 7.20m.

If you increase the focusing distance to 3.6m, the HFD will not change (still 7.20m). However, the DoF will increase to 4.75m.

If you increase the focusing distance to 7.2m (same as HFD), the DoF will be infinite. However, half the focusing distance (from the camera, 3.6m) will be out of focus. The infinite DoF will start from 3.6m in front.

If you focused past HFD (10m, for example), you’d not see any difference (3.60m to infinity will be in focus). I did make a mistake earlier suggesting that infinite DoF will start at 5m. It will always start at half the distance to HFD as long as the minimum focusing distance equals HFD.

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