DPReview.com is closing April 10th - Find out more

Lens starburst at fully open aperture

Started Feb 17, 2022 | Discussions thread
J A C S
J A C S Forum Pro • Posts: 20,544
Re: Lens starburst at fully open aperture

Atis photo wrote:

Sittatunga wrote:

I don't have that RF zoom, but other constant aperture zooms I do have achieve their constant aperture by stopping down the iris towards the wider end of the zoom.

WOW, that's a new one for me! That might be the issue! So in reality, at wider end of the zoom, the lens might be brighter than f4, say f3? And it is stopped down to f4 just so that it matches fixed aperture of f4?

This lens opens fully at the long end only, indeed. There is no conspiracy here. Take a look here. The off-corner mechanical vignetting is much stronger than what the physical diaphragm does. If you open the aperture somehow more, a large off-center part will get no extra light; you will get a hot spot in the central part only. In other words, the vignetting would be horrible.

And no, it is not a crippled 24/0.95 lens...

Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow