DavidBM
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I have been using JJC dome hoods on a few lenses for a while; in particular the Sigma i90 and the Apo Lanthar 2/50.
I tested them for light fall off before use; not visible corner darkening, no obvious vignetting in the focal plane with simple testing.
I naively assumed that would be fine (which it mostly is of course, but.....)
Reading about how a certain lens when rehoused created mechanical vignetting with the sensor mask on some brand, it occurred to me that the domes could cause mech. vig without much impact on the focal plane. I may get around to testing actual bokeh ball shape, but I thought I should just do a bokeh test first.
These crops are 50%, and show about half the image height of the lens. All are on a tripod, no change in light on overcast day (clearer difference on bright day I expect) and focussed in front of the bokeh.
In each case the left image is the original hood, the right a dome hood.
On some lenses the dome will be perfect. But don't assume this until you have tested either the bokeh ball shape, or the OOF.
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