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What Is a Parfocal Lens?
A parfocal lens is a lens that remains in focus even as the magnification or focal length changes. Parfocal lenses allow the user to zoom in on a subject and zoom back out while maintaining the same focus.
Parfocal zoom lenses are not just used in photography: they are also common in microscopes and telescopes.
3 Reasons to Use a Parfocal Lens
Parfocal zoom lenses generally make life easier for photographers and videographers because they do not require a manual readjustment of focus every time the zoom range changes.
- A parfocal zoom lens maintains focus as the focal point changes and the lens is zoomed (changing both focal length and magnification).
- A parfocal lens allows for more accurate focusing at the maximum focal length, and then quick zooming back to a shorter focal length.
- Parfocal lenses also ameliorate lens breathing, a common headache for photographers. Lens breathing happens with varifocal lenses when, as the photographer adjusts the focus, the edges of the frame begin to shift, moving in and then out. This is particularly problematic when shooting video, where the viewer can actually see this unfold frame by frame. By staying in focus while zooming, parfocal lenses avoid this problem. This is why videographers prefer working with parfocal lenses.
What Is the Difference Between a Parfocal and Varifocal Lens?
Parfocal lenses automatically maintain focus while zooming in and out, while varifocal lenses do not. A parfocal zoom lens is always in focus, regardless of the change in zoom range; a varifocal lens must be manually refocused every time the zoom range is changed.
- Varifocal lenses are most practical for shooting still photography, where the photographer is often refocusing their lens for each individual composition.
- Parfocal lenses are most common in videography and sports and wedding photography. Parfocal lenses allow for a rapid shifting within the field of view—from one character to another, from one depth to another, and from one object to another—all while maintaining the same focus.
How to Use a Parfocal Lens
With modern digital photography and lens design, much of the work of using a parfocal lens is already done for you: the lenses maintain focus automatically, adjusting for any focus shift or focus shifts that occur during zooming. Thus, there is little additional work required by the photographer, who does not need to change the focus to compensate for the zoom.
However, in some situations, a varifocal lens is preferable over a parfocal lens. This is especially true in still photography and situations where a photographer needs to assert absolute control over every aspect of a photograph.
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