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Thread: Bokeh defects?

  1. #1
    milleniummuppet's Avatar
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    Bokeh defects?

    Hi there,

    Haven't been here in a very long time, thought it would be a good place to ask this question.
    I've recently shot these images at the local public fireworks using an old 50mm Nikkor lens on a DSLR body experimenting with depth of filed in low light, and noticed some really ugly shapes in the images! Does anyone know exactly what they are? They only really show up in this kind of image, but are annoying regardless, particularly since I'm interested in using the lens to shoot short films at some point.

    http://imgur.com/a/PTSKx - for some reason the 3rd image is broken on imgur, full res version is fine.

    Matt.

  2. #2
    rpcrowe's Avatar
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    Re: Bokeh defects?

    Did you by any chance have a UV or other protective filter on this lens?

  3. #3
    milleniummuppet's Avatar
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    Re: Bokeh defects?

    Quote Originally Posted by rpcrowe View Post
    Did you by any chance have a UV or other protective filter on this lens?
    Nope, no filters.

  4. #4
    ktuli's Avatar
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    Re: Bokeh defects?

    My first guess would be dirt either on the front or rear of the lens (most likely, rear).

    Hopefully it isn't inside the lens!

    - Bill

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    Re: Bokeh defects?

    Hi Matt,

    The patterns repeat -it must be dirt. Check your lens front and rear and do a test to see how dirty the sensor is.

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    MilT0s's Avatar
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    Re: Bokeh defects?

    My guess too. It looks like it is on the optics, not the sensor sice it is repeated.

    Could be inside the lens but probably on the front element I think.

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    Re: Bokeh defects?

    Looking at the last shot with the wet umbrella I suspect the main problem is that the lens wasn't focused on the fire works. The brolley is clearly in focus and close to the camera. A secondary problem may well be water drops on the lens's front element as there appears to be a lot of flair as well but this could be more down to the light from the fireworks. I would also expect the brolley to be under exposed so some of the problem could also be too long an exposure for these particular fire works..

    -

  8. #8
    milleniummuppet's Avatar
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    Re: Bokeh defects?

    Quote Originally Posted by ajohnw View Post
    Looking at the last shot with the wet umbrella I suspect the main problem is that the lens wasn't focused on the fire works. The brolley is clearly in focus and close to the camera. A secondary problem may well be water drops on the lens's front element as there appears to be a lot of flair as well but this could be more down to the light from the fireworks. I would also expect the brolley to be under exposed so some of the problem could also be too long an exposure for these particular fire works..

    -
    Hey there, the fireworks are intentionally out of focus in these shots for the purpose of testing the cleanness of the Bokeh, I will have another good inspection for dirt etc on the lens though. Cheers guys

  9. #9
    milleniummuppet's Avatar
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    Re: Bokeh defects?

    Upon closer inspection, there is no dust or dirt visible which would be causing it, but I found something else shocking, its only visible if the aperture blades are completely closed and held at exactly the right angle. Had a very hard time taking the photos.
    The pattern definitely looks like it matches up (except for in the images there is more than one blob aside from the main one). It looks to be on one of the elements underneath the top one any idea what it is? its not solid, its see through but only visible as an oily wavy looking thing at certain light angles? Doesn't effect image quality when the image is in focus, only out of focus, light flare type situations, (much like dust rarely effects image quality).

    I wonder if its some sort of problem happening with a coating? The small round spots in my images could well be rain drops since this strange thing behaves a little like one itself.

    Bokeh defects?

    Bokeh defects?
    Last edited by milleniummuppet; 9th November 2012 at 08:13 PM.

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    Re: Bokeh defects?

    The best Boken effects are those where as the background is father away.

  11. #11
    Glenn NK's Avatar
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    Re: Bokeh defects?

    Before taking a stab in the dark, some basic information would be useful:

    Aperture at which lens was used
    Distances to primary subject and to OOF elements

    At least one of the 50 mm Nikon lenses is known to some outlining and "nervous" bokeh (Photozone lists two f/1.8 lenses that have been tested).

    http://www.photozone.de/nikon--nikko...50_14g?start=1

    Bokeh generally isn't referred to as having "defects", but whether or not the bokeh is pleasing or not pleasing.

    A good read on the topic:

    http://www.rickdenney.com/bokeh_test.htm

    Glenn

  12. #12
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    Re: Bokeh defects?

    Looks like delamination of a cemented lens element. I've seen it in old large format lenses. It's not normally thought to affect picture quality but the effect on the bokeh is interesting.

  13. #13
    milleniummuppet's Avatar
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    Re: Bokeh defects?

    F1.8, distance to subject, well fireworks in sky, over waterfront, maybe 100+ meters ? Focus distance was probably around 4-5 feet, had my hand been that distance away in the frame it would have been in focus. The weird thing is that its not just distortion or anything, and that light is physically not reaching the sensor in such a weird form. Not sure hat OOF elements are?

  14. #14
    milleniummuppet's Avatar
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    Re: Bokeh defects?

    Quote Originally Posted by oleleclos View Post
    Looks like delamination of a cemented lens element. I've seen it in old large format lenses. It's not normally thought to affect picture quality but the effect on the bokeh is interesting.
    Do you know if this is this something that gets worse in certain conditions etc?

    Yea this seems to be what it is
    Bokeh defects?
    Last edited by milleniummuppet; 9th November 2012 at 10:01 PM.

  15. #15
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    Re: Bokeh defects?

    Delamination isn't usually just a wavy "stripe" like the one shown in you photo. It usually starts at the edges and can spread right across an element. The torch mentioned is the best bet for checking and can be "improved" with a magnifying glass as that makes it more easy to see into the lens. It's also a good idea to rotate the lens when you can see marks and make sure it moves with it. The magnifying glass will also show up marks in the coating more clearly. That would be my favourite but it looks like it's deep in the lens.

    The odd thing about the brolley is some of it that should be in focus isn't which is why I mentioned rain drops on the glass. They could do all sorts of bizarre things.

    -

  16. #16
    Glenn NK's Avatar
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    Re: Bokeh defects?

    Matt:

    The regular patterns in first image are disturbing - each bright circle has the same pattern of dots and one squiggly line - poor bokeh of specular highlights just doesn't look like that. A repeating pattern isn't something one would expect from a bright light source such as fireworks or specular highlights on a wine glass (first example of linked article).

    I think Ole might be onto something - the best check would be to use another copy of the same lens. Fireworks are not likely going to be easy to find again, but two lenses could be compared by shooting some oof lights in the background.

    Glenn

  17. #17
    milleniummuppet's Avatar
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    Re: Bokeh defects?

    Yea good plan, I shall have to acquire myself another one.

  18. #18
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    Re: Bokeh defects?

    Quote Originally Posted by milleniummuppet View Post
    Upon closer inspection, there is no dust or dirt visible which would be causing it, but I found something else shocking, its only visible if the aperture blades are completely closed and held at exactly the right angle. Had a very hard time taking the photos.
    The pattern definitely looks like it matches up (except for in the images there is more than one blob aside from the main one). It looks to be on one of the elements underneath the top one any idea what it is? its not solid, its see through but only visible as an oily wavy looking thing at certain light angles? Doesn't effect image quality when the image is in focus, only out of focus, light flare type situations, (much like dust rarely effects image quality).

    I wonder if its some sort of problem happening with a coating? The small round spots in my images could well be rain drops since this strange thing behaves a little like one itself.

    Bokeh defects?

    Bokeh defects?
    I think I can identify the problem, based on something small but clearly visible in your image.
    If you look at the edge of the lens, it is very subtle, but you can clearly make out the word "Nikon"...

    (Just kidding!)

  19. #19
    milleniummuppet's Avatar
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    Re: Bokeh defects?

    Quote Originally Posted by Scott Stephen View Post
    I think I can identify the problem, based on something small but clearly visible in your image.
    If you look at the edge of the lens, it is very subtle, but you can clearly make out the word "Nikon"...

    (Just kidding!)
    Haha. Indeed, should be 'Voigtlander', It's ok I'll fix later.

  20. #20
    MilT0s's Avatar
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    Re: Bokeh defects?

    That's very interesting.

    Could be either the glue of a doublet lens element (red arrow, my guess too) or a coating scratch. In any case it is a lens material failure.

    Was the lens exposed to heat (e.g. sun or next to a heating device) or shock (e.g. dropped) ?

    Bokeh defects?

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