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what caused these???

Discussion in 'Through-the-Lens Club' started by nipperwolf, Jan 15, 2006.

  1. nipperwolf

    nipperwolf

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    heres the pic

    [​IMG]

    D50/18-55 kit lens. f5.6, 1.6sec. shot in RAW. auto wb.

    here's the spots above the courthouse.

    [​IMG]

    my guess is those were caused by the lights on the bridge that were to my right. I didn't have a lens hood at the time.

    here's the other 2 spots that are completely different.

    [​IMG]

    [​IMG]

    they all have the same shape. guy at my shop said he's never seen these kind of spots before.

    any ideas?

    thanx.
     
  2. allanc

    allanc "Inconceivable"

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  3. hwyhobo

    hwyhobo

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  4. nipperwolf

    nipperwolf

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    cat got your tongue? ;)

    anyway, here's the scoop. they're not lens flares. while I thought the 2 above the courthouse might be, it was the other spots I was unsure of.

    they are reflections from the sensor back to the rear element of the lens. here's an uncropped pic connecting the dots.

    [​IMG]

    here's the explanation from a member at the Nikonians site;

    "They appear to be reflections off of the sensor that were then reflected back be the rear element of the lens.
    Go back to an uncropped version of the original image and find the exact center. Draw a line from one of the mystery objects to the center and then continue in a straight line the same distance again and you will find a bright light source. It seems the posted image has a noticable portion of the right side cropped off based on the aspect ratio (not 1:1.5 of a D50) and the node about which all of the mystery spots seem to be reflected. The center would seem to be near the brightly lit portico on the left side of the building with the clock tower.

    There are also two in the sky each side of the clock tower that map to two of the lights in the lower left quarter of the picture.
    Reflections like these are almost certainly a sensor to lens and back to sensor reflection. Internal lens reflections and lens to filter reflections don't form patterns that are radially reflected about the center of the image. They form a pattern of reflections along a line toward the center but on the same side of the center unless they are bright enough to form secondary and tertiary patterns that can then extend beyond the center. Internal lens reflections generally don't (I've never seen one that did) form their primary, brightest reflection on the opposite side of the center."
     
  5. Dandapani

    Dandapani

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    neat explanation. is there a solution?
     
  6. hwyhobo

    hwyhobo

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    Hehe... I was about to join the front flare diagnosis combined with internal flare when I spotted some reflections that didn't quite fit, so I decided to do some research first. You covered it in your post. Now, I am not sure, but a lens with better coatings in the back of the lens may fare better.

    I am still not 100% sure that internal flare did not contribute to it, whether the non-image-forming light entered from the front or rear.
     
  7. nipperwolf

    nipperwolf

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    some members in a couple forums suggested it could be the filter causing it. the weather finally cooperated so that I could duplicate the pic, without the filter.

    pic with filter

    [​IMG]

    removed the filter, and....

    [​IMG]

    spots are gone.

    the filterless pic was also sharper

    [​IMG]

    don't know if a higher quality filter would have produced the spots or not, or wouldn't have degraded the sharpness.

    or wether the spots were sensor reflections caused by the filter.

    but, I'm now rethinking my take on filters.

    probably only for effect. for protection only in extreme conditions, like a motocross race or something similar that could produce projectiles.
     
  8. hwyhobo

    hwyhobo

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    Oh, that's great! Makes me feel good a little bit that I wasn't sure to the end whether the light that caused the reflections entered from the front or rear. ;b

    It also vindicates somewhat my stubborn position that you don't pay for good glass to waste it with a cheaper glass in front. ;a Out of curiosity, what filter was that? Did it have good coatings? Was it B+W MRC or Hoya HMC?
     
  9. nipperwolf

    nipperwolf

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    it was a Tiffen Skylight 1A. ;Q

    I'll probably pick up a Hoya multi-coated and test it the same way.

    tried a few shots of the full moon earlier this month. had to do some major cropping since I was just using my 70-300D lens. still, I thought it should have looked a little sharper.

    I just checked, and the filter on it is also a Tiffen Sky 1A. I'll try the moon next month without the filter.;)
     
  10. hwyhobo

    hwyhobo

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    Besides possible reflections, skylight filters give color cast. If you must use a filter for protection, perhaps a good quality UV?
     
  11. nipperwolf

    nipperwolf

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    did a quick check on my other lenses. the filter on my new 50mm 1.8 is a Hoya UV. UV was recommended by my local shop, also. its coated, but not multi-coated. the filter on my 80-200 f2.8 is a Hoya skylight.;Q

    first, I plan to do some testing on the hoya UV on the 50mm to check for sharpness loss, if any. then maybe a some UV filters for my zooms.

    I'm also giving alot of thought now to the need for filters for protection. in over 20 years of using them for that, I've never even scratched a filter.

    knock on wood.;)
     
  12. hwyhobo

    hwyhobo

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    Bingo. That has been my experience as well. I believe a good, rigid lens hood gives a better protection without the price in quality loss.