Alley in Pisa, Italy

by Lars Kotthoff

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Take a look at the thin lens formula (image taken from Wikipedia): S1 here is the distance between the subject and the lens, and S2 is the distance from the lens to the spot where the image of the subject is formed. f is the focal length of the lens. You can see that as distance S1 gets smaller, S2 has to get larger to compensate. That is, as you move ...


With a certain distance to the subject, it is in focus at a certain distance to the image sensor. As you move closer to the lens, the place it is in focus moves back. this is because the lens property to bend light is in principle fixed and as you move closer, you change the incoming angles. Naturally, something has to compensate for this, and the distance ...


The answer is the a Len has two parts a focal length (zoom) and a focal distance (focus). Sticking to a fixed focal length lens. They are sold with the ability to focus from infinity to a close distance. What this is the ability to focus to a point lines the hit the front of the lens parallel (infinity) and bend those to hit the focal plane (film or ...


No. Extension tubes that offer AF capability simply mean they have contacts that allow for electronic communication between the body and the lens. They do not have autofocus motors in them or add autofocus capability to a body/lens combination that doesn't have it without the extension tubes.

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