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Thread: Super angulon No Flare construction

  1. #1

    Super angulon No Flare construction

    So I was browsing kenrockwell.com and came upon an interesting article he wrote about the f8 super angulon. He claims these lenses produce no flare or ghosting and can even be shot directly into a light source with no I'll effect.

    Quoted below:
    "I doubt coating makes any difference in anything except a subtle difference in color transmission since these have no ghosting or flare; feel free to shoot straight into the light.*"

    I have noticed no flare in my own SA but didn't think much of it other than gee I got lucky. Does anyone know what attribute or construction mechanic allows this lens to be free from these phenomena?

  2. #2
    I live in Connecticut now.
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    Re: Super angulon No Flare construction

    I've actually been curious about this too with lens designs, I always thought flare was in every lens and changed look based on aperture shape.

    Curious about flare (or non-flare) for lenses like the SA, Symmar, Tessar, Dyalite, designs as well as others (simple meniscus?).

    Looking forward to more experienced lens folk commenting.

  3. #3

    Re: Super angulon No Flare construction

    Lens design definitely affect flare suppression. Some Leica lens flare like mad, some don't. The Fuji designed XPan lens are all excellent in flare suppression and I have many XPan shots with the Sun in the frames.

    Beats me what kind of magic dust or formulas they use though.

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    Re: Super angulon No Flare construction

    it's a superb lens as many knows, but it can be seen clearly that it flares in closed angles to the source light, as in this pic - the first one made with a pristine SA 8/90 recently bought, with the Sinar F2:

    6372+73_v3 by Renato__ Salles, on Flickr

    Renato

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    IanG's Avatar
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    Re: Super angulon No Flare construction

    Quote Originally Posted by RodinalDuchamp View Post
    Quoted below:
    "I doubt coating makes any difference in anything except a subtle difference in color transmission since these have no ghosting or flare; feel free to shoot straight into the light.*"
    There's something wrong with Ken Rockwells statement as all the 90mm f8 Super Angulons are coated and Schneider's coatings (pre-Multicoating) were very good, they did improve and later Black barreled Super Angulons had very effective coating.

    I'd guess he's talking about coated lensed compared to Multi-coated. I've not had flare problems with any of my coated Super Angulons all 3 pre-MC, and I also use a CZJ 150mm f5.6 T (coated) Tessar or a late 150mm f5.6 Xenar both remarkably flare free in conditions where my DSLR lenses are unusable.

    Ian

  6. #6
    Nodda Duma's Avatar
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    Re: Super angulon No Flare construction

    Coatings are only the closing pages of the story in reducing lens flare. From an optical design point, you better not wait until the lens coatings are specified to eliminate lens flare or you will not eliminate lens flare!

    Ok first things first... lens flare can mean several different things (read the first paragraph on the Wikipedia page). In optical design we use the generic term stray light. Stray light analysis is performed during the design to uncover these issues and correct for them:

    - Ghosting or ghost artifacts (secondary focused or near-focused image of bright objects both on- and off-axis caused by double reflection off optical surfaces)

    - Veiling Glare (general loss of contrast. Veiling glare is basically very defocused ghosting, arising from double reflections )

    - Narcissus (re-imaging of the image plane or loss of contrast from back-reflection in the optics. Can contribute to non-uniform illumination or, worst case, reimaging of the image onto itself with some offset due to assembly tolerances).

    - Secondary path artifacts (stray light paths not intended by the optical design. Often times from off-axis sources with glancing reflections off the interior of the lens barrel or inside of the lens edge).



    These must all be analyzed and controlled to one extent or the other depending on the intended use of the imaging objectives. In all cases, veiling glare and secondary paths are analyzed. Ghosting is usually controlled unless it is desired for artistic purposes. Narcissus won't really apply to film camera lenses (except when the lens is designed for digital imaging as well).


    Veiling glare

    Veiling glare always happens and is controlled by the coating spec. It is caused by optical paths involving multiple reflections (usually just two need to be tracked) on the lens surfaces reaching the image plane. These paths do not create a focused "secondary" image or even necessarily a converging light cone at the image plane...it is just unwanted extra light hitting the image plane from bright objects in your scene. With this unwanted defocused light, dark portions of the scene are not as dark and the result is you get a loss of contrast. You *always* have veiling glare reducing your contrast -- even if there's not any specific bright object in the scene -- and it must be controlled by coating (the modern approach) or minimizing the number of air-glass surfaces (the favored approach before coatings were developed). So that's what coatings help. But that's only one of the stray light issues.

    This is why a coated lens gives you more contrast than an uncoated lens with the same air-glass interfaces. You can't really eliminate or even reduce veiling glare except for by coating the optics and a trick or two with ghost artifacts as described below.



    Secondary path artifacts

    Secondary paths are reduced / eliminated by the lens barrel design. Baffling, helical or groove cuts, and flat black paint on the interior barrel and the lens edges are all used for controlling secondary stray light paths. The paths usually originate outside the intended field of view.. You can see the artifacts by aiming the lens towards a bright object like a flashlight (NOT the sun! Don't burn your retina) with the object just outside the camera's field of view. That "flare" is from these paths.


    Ghost artifacts

    Ghost artifacts or ghost images are sometimes desired for artistic effect. For other uses such as scientific imaging or for night vision imaging they are absolutely unwanted and must be controlled. Ghost images can include secondary images of the scene and images of the aperture stop. Aperture stop ghost images can be an issue when the aperture is buried such as for a double gauss design. I don't see problems with it when the first lens serves as the aperture stop (common for the fixed aperture narrow field-of-view objectives that I've been doing a lot of lately).

    Ghost artifacts include the traditional aperture stop images you see in the old Westerns when the camera pans across the landscape looking near or at the sun. Ghost imaging analysis is performed to determine what optical surfaces are causing problems, and the surface curvatures tweaked or the lens spacing adjusted to eliminate the in- or near-focus ghost images. This corrective action transforms the ghost artifact into veiling glare, which is then more easily controlled with coatings and baffling.

    One more point about ghosting: You can also ignore it if the ghost image falls perfectly on the primary image. Then in assembly you ensure the optics are aligned well enough that the primary and ghost still fall on each at the image plane. I've done this before in a couple of situations where I couldn't move or adjust the lenses enough to defocus the ghost path. he benefit is that you have that much less veiling glare to worry about.



    Narcissus

    Discussion of narcissus is kind of OT since it is almost never a concern with traditional film, but can be an issue with digital imagers and especially thermal imagers. You do not want the structure of your focal plane array to show up in your image! That's the worst case. More often, narcissus has an impact on scene non-uniformity. While thermal imagers provide for non-uniformity correction (necessary as the camera heats up), if the non-uniformity is too great then you run into gain-related noise issues in the images. That means you didn't do your job as a designer.



    Basically there's a lot of $#!% to consider, and the stray light analysis is a considerable part of the design effort.


    So for the lens in this thread, if they say you can point it at the sun without lens flare, it means the designer did a good job of eliminating the secondary paths which set up ghost images and stray light artifacts. The coatings are good too, but are not the primary reason for lack of lens flare.

    Regards,
    Jason

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