Shutter behind a larger lens

[Ian Leake]

I saw this video on Instagram:

In the captions he writes: "The lens diameter is noticeably larger than the shutter, but this has no effect on the aperture. it only reduces the image circle..."

That statement seems wrong to me. Surely placing a smaller opening behind the lens will also reduce the effective aperture?

 

[Dan Fromm]

I saw this video on Instagram:

In the captions he writes: "The lens diameter is noticeably larger than the shutter, but this has no effect on the aperture. it only reduces the image circle..."

That statement seems wrong to me. Surely placing a smaller opening behind the lens will also reduce the effective aperture?

It depends on the lens and lens-shutter geometry. I've hung barrel lenses in front of shutters and a shutter in front of a lens. Vignetting can be a problem. Loss of speed much less so.