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  1. #1
    Markster's Avatar
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    Controlling bokeh on 500mm mirror lenses?

    I've been reading reviews and comments on 500mm mirror lenses today. There is, of course, mention of the donut-shaped bokeh for out-of-focus light reflections. However, some folks seem to have mastered the bokeh to the point that backgrounds simply look out of focus as with any other lens.

    It's not something I've thought about too much, so I'll ask: With such a lens, what would you do to minimize it? What are some of the basic tricks?
    -Markster

    Canon AE-1P 35mm | 50mm/f1.8 FDn | 28mm/2.8 FD | 70-200mm/f4-5 FD | 35-70mm/F2.8-3.5 Sigma FD

  2. #2
    polyglot's Avatar
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    For the donuts to be invisible, you need to make sure that the smallest spatial frequency in your image (i.e. detail) for an out-of-focus area is larger than the bokeh-size for that out-of-focus region.

    In other words, if you have point-lights (e.g. light glittering off rippled water, streetlights, fairylights, etc), then you will get unavoidable donuts. If the background is all fairly uniform in tone and has no fine features (points or lines) with strongly separated tones, then it will all tend to blend together despite the donut bokeh.

    If you're shooting birds against the sky, you get no issues. If you shoot birds in front of shrubbery, the shrubbery can look bad because all the lines get doubled.

  3. #3
    Markster's Avatar
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    Interesting... Thanks!
    -Markster

    Canon AE-1P 35mm | 50mm/f1.8 FDn | 28mm/2.8 FD | 70-200mm/f4-5 FD | 35-70mm/F2.8-3.5 Sigma FD

  4. #4
    nicholai's Avatar
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    Sometimes, i feel like i'm the only one that likes the mirror's bokeh. As a means of pictorial expression, i like the it. Some real cool tricks can be done with it. (eg: THIS)
    Nicholai Nissen
    Kolding, Denmark
    nicholainissen@gmail.com

  5. #5

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    I loathe mirror lens bokeh. By far, to my eyes, one of the ugliest things you can ever put into a photograph.

  6. #6
    Matthew Wagg's Avatar
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    Quote Originally Posted by nicholai View Post
    Sometimes, i feel like i'm the only one that likes the mirror's bokeh. As a means of pictorial expression, i like the it. Some real cool tricks can be done with it. (eg: THIS)
    That is very cool. What lens is it you used for it. I know there's a lot of variance in the quality of catadioptric lenses.

  7. #7

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    I recall a discussion with a photographer way back (20+ yrs) who maintained that using a 1.4x TC reduces or removes the donut shaped highlights. I can't understand why it would work, and haven't got a mirror lens to try it with, but maybe someone here can try it and give feedback. As for the effect in nicolai's example, that's about as good as it gets and even then I find it very distracting. In fact, it almost makes me motion sick looking at that pic. Sorry, just my humble take on it - no intention to offend.

  8. #8
    vpwphoto's Avatar
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    Nothing wrong with the doughnut other than if you use it a lot it can be repetitive... I like the "boat" photo referred to, I shot rugby with one once and got some neat images. There will likely be somebody soon that will make it a "thing" and everyone will want one. I think I will start stocking up on them now.

  9. #9
    Maris's Avatar
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    I get rid of the donut bokeh of mirror lenses by fitting an off-centre circular aperture on the front of the lens. The circular aperture has got to be small enough to avoid the central obstruction. Off-centre apertures can be made in smaller and smaller sizes thus stopping down a mirror lens; a procedure popularly thought to be impossible. Downside? The viewfinder image gets dim. Upside? Better bokeh and more depth of field.
    Photography, the word itself, invented and defined by its author Sir John.F.W.Herschel, 14 March 1839 at the Royal Society, Somerset House, London. Quote "...Photography or the application of the Chemical rays of light to the purpose of pictorial representation,..". unquote.

  10. #10
    Markster's Avatar
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    I wonder how such a lense would do with astronomy shots... Anybody tried it, or know?
    -Markster

    Canon AE-1P 35mm | 50mm/f1.8 FDn | 28mm/2.8 FD | 70-200mm/f4-5 FD | 35-70mm/F2.8-3.5 Sigma FD

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