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Thread: Opinion on magenta "bands" ?

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    Question Opinion on magenta "bands" ?

    Hi all,

    New to the tech cam world, I just got a brand new Rod 40 HRW to use with my Rm3di and Aptus II 7.
    Weather being what it is in northern France in February, my first tests shots were under some really greyish skies... that's how I noticed some very subtle magenta bands across the frame, even with all movements zeroed.

    Now I'm aware casts are to be expected, and that's what LCCs are for, but the pattern here is something I have no idea how to interpret.
    At first I thought it could be an issue with the back, but since those bands seem to "move" when I shift left and right, I'd assume it has something to do with the lens ? Or maybe this is all normal and I worry too much about it...

    Attached are LCC shots with the color cast option unchecked in C1 7 : 15mm left shift, center, 15mm right and 2 panos.
    Obviously I've exaggerated the effect a bit for you to see the pattern better, though it was strong enough for I notice in a normal shot first.

    Looking forward to your diagnostics and opinions here !
    Thanks

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    Senior Member Pemihan's Avatar
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    Re: Opinion on magenta "bands" ?

    Have you tried to make a copy of one of the LCC's and apply it to the original LCC.
    I would assume that would remove the color cast...

    Peter

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    Re: Opinion on magenta "bands" ?

    Peter,
    If I build a LCC from those and check the color cast option those bands disappear almost entirely indeed, and the end result is totally acceptable.
    I guess I'm just being curious as to where such alternating vertical bands come from. I've been reading a lot on the topic recently yet can't remember of a similar pattern being discussed.

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    Re: Opinion on magenta "bands" ?

    FWIW I've sent Arca an email, hopefully will report back soon.

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    Re: Opinion on magenta "bands" ?

    I think it looks normal, assuming the contrast has been increased on the LCC shots.

    One might think that the color cast should have the shape of vignetting, that is circular outwards from the center. That was what I believed when I started out with my tech cam. However, a sensor don't have perfectly uniform response concerning color cast (i e some parts of the sensor can have more cast issues than others) which causes this pattern to occur.

    After LCC correction it should be 100% invisible though. If it is not, then maybe your digital back have some problem.
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    Thumbs up Re: Opinion on magenta "bands" ?

    Thanks Torger, that totally makes sense. I thought that the change of pattern while shifting implied a lens issue, but I may be used to color cast on film a bit too much...

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    Senior Member yaya's Avatar
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    Re: Opinion on magenta "bands" ?

    Frederic when creating LCCs make sure you check the "Technical Wide Angel" box. These images look normal to me with the 40mm and considering they were pushed a bit

    Enjoy your new back!

    Yair
    Yair Shahar | Product Manager | Phase One | Mamiya Leaf
    e: [email protected] | m: +44(0)77 8992 8199 | yaya's blog
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