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There has been discussion on a couple of recent threads about the bokeh produced by mirror lenses. Usually when this subject comes up it is almost immediately followed by the word "doughnut" - the design of the lens, with a concentrator mirror in the middle of the front element, makes out of focus points show up as rings rather than disks. This can be attractive, for example with specular highlights on water it can look really dreamy. It can also be horrible.
I occasionally used one back in film days when shooting cricket, and remember that sometimes out of focus foliage in the background could look really awful. I will try and find some examples, but it means a physical delve into the film archives. I found the old Olympus 500mm f/8 lens and adapters to stick it on the E-M1 and took a few samples this aftie. It was quite difficult to find a suitable subject for such a long lens without going out into Covid-restricted territory.
Here are the results. The first is a general shot (with the 14-150) to provide context, then three with the mirror lens at different points of focus, and three with the nearest equivalent m43 "straight" lens I have, the 300mm f/4 with 1.4x converter. All are the whole frame, completely unedited except to resize for the web.
Context shot:
According to the EXIF on later shots, the brick wall is about 13 metres away, the bush with the pinky blossom about 19 and the brightly-lit green bush in the background about 42.
One with the mirror lens focused on the brick wall (the wall part rather than the gate parapet):
The pink bush looks a bit doughnutty but the further one has more conventional blur.
Mirror lens focused on pink blossom:
You want doughnuts? We got 'em - fore and aft!
Mirror lens focused (badly) on the background bush:
And just for completeness, mirror lens focused way off, possibly at minimum distance, to blur everything:
For comparison, three with the 300/4 and MC-14, focused on the wall, the pink blossom and the background bush:
I am almost disappointed that the mirror lens bokeh isn't too awful in any of these! What is shows quite clearly is that the degree of doughnutting depends a lot on how far out of focus the subject is. If it is far enough out of focus it just blurs almost like any other lens. I suppose this should have been obvious but it had never occurred to me before.
That was fun. I hope it is also at least a little bit interesting and instructive. In general I think the old Oly mirror lens acquitted itself quite well. It was a beast to focus though, at that long focal length the image skips around crazy, even on the tripod.
John
I occasionally used one back in film days when shooting cricket, and remember that sometimes out of focus foliage in the background could look really awful. I will try and find some examples, but it means a physical delve into the film archives. I found the old Olympus 500mm f/8 lens and adapters to stick it on the E-M1 and took a few samples this aftie. It was quite difficult to find a suitable subject for such a long lens without going out into Covid-restricted territory.
Here are the results. The first is a general shot (with the 14-150) to provide context, then three with the mirror lens at different points of focus, and three with the nearest equivalent m43 "straight" lens I have, the 300mm f/4 with 1.4x converter. All are the whole frame, completely unedited except to resize for the web.
Context shot:
According to the EXIF on later shots, the brick wall is about 13 metres away, the bush with the pinky blossom about 19 and the brightly-lit green bush in the background about 42.
One with the mirror lens focused on the brick wall (the wall part rather than the gate parapet):
The pink bush looks a bit doughnutty but the further one has more conventional blur.
Mirror lens focused on pink blossom:
You want doughnuts? We got 'em - fore and aft!
Mirror lens focused (badly) on the background bush:
And just for completeness, mirror lens focused way off, possibly at minimum distance, to blur everything:
For comparison, three with the 300/4 and MC-14, focused on the wall, the pink blossom and the background bush:
I am almost disappointed that the mirror lens bokeh isn't too awful in any of these! What is shows quite clearly is that the degree of doughnutting depends a lot on how far out of focus the subject is. If it is far enough out of focus it just blurs almost like any other lens. I suppose this should have been obvious but it had never occurred to me before.
That was fun. I hope it is also at least a little bit interesting and instructive. In general I think the old Oly mirror lens acquitted itself quite well. It was a beast to focus though, at that long focal length the image skips around crazy, even on the tripod.
John
) also had a 'solid' catadioptric design that enabled the physical size of the lens to be very short compared to a conventional lens.
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