Why does focus shift when I zoom out on my Sigma 18-200mm?
Asked 4/19/2013
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2 answers
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With my Canon kit lens, I could zoom all the way in, focus on a subject, then zoom back out and the subject would stay in focus. On my Sigma 18-200mm used on a Canon 600D, the focus changes after I zoom out and I have to refocus. Is this normal behavior for some zoom lenses, or could the lens be faulty?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
13
The lens is a varifocal lens. Basically, it's a lens that changes focus as the focal length changes and it's quite common. Parfocal lenses, ones that maintain focus on zoom change, exist but are typically more expensive as a result.
Long story short, it's normal for a large number of consumer zoom lenses.
Originally by user472. Source · Licensed CC BY-SA 4.0
user472
13y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—this can be normal. Many consumer zoom lenses are varifocal, which means changing the focal length also changes the focus point. With those lenses, if you focus while zoomed in and then zoom out, the subject may no longer be in focus and you’ll need to refocus.
A lens that keeps focus as you zoom is called parfocal. Those exist, but they’re less common and usually found in more specialized or higher-end designs.
So based on your description, your Sigma 18-200mm is not necessarily broken; it likely just isn’t a parfocal zoom.
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