Lenses in the still photography world are just one group of lenses out there, and if you haven't done much work in cinema or broadcast, then you might not have ever considered why you might want to invest in other kinds of glass. However, as more photographers are finding themselves getting into short film production, the benefits of using parfocal lenses should be considered.
As someone who has used broadcast camera systems for documentary projects, I can absolutely attest to the benefits of parfocal lenses. Being able to keep focus through your zoom allows for more opportunities of creative control, and way less missed shots due to bad focus. Honestly, breathing never bothered me too much when using still lenses, but on cheaper glass where the breathing is significant, it can be rather annoying.
The Fujinon MK 18-55mm T2.9 is the parfocal lens that is shown in the video, and is available for pre-order. I'm very excited to rent this on a future shoot, as it looks to be exactly what I want in a documentary lens setup. Check out this article for a write up that includes reviews and feature listings.
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