Vignetting issues with CPLs and UWA lenses - my solution!
  • beeb
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    Vignetting issues with CPLs and UWA lenses - my solution!

    by beeb » Fri Apr 27, 2012 6:24 pm

    A few of you might remember me complaining about suffering from strong vignetting at the corners of the frame when using the Cokin Z-Pro setup at 16 or 17mm on my 5DII.

    Well, This was my solution - A custom-machined adapter, to allow the Cokin CPL (which is very thin even with its flanged frame) to be held securely by the Lee 100mm Filter holder.

    Image
    Custom Cokin CPL to Lee Filter Holder Adapter by T. Flack, on Flickr

    Because Lee holder-to-lens adaptor rings can be bought in 'wide-angle' varieties (which place the filter closest to the camera almost flush with the end of the lens), adapting the slot-in style Cokin Z-Pro (Z164) CPL (which normally sits several mm away from the end of the lens in the Cokin setup) allows a much wider AOV to be obtained without vignetting. Testing showed that vignetting/clipping was only noted down the very edges of the frame with my 16-35mm L II when it was set (at 16mm) to the minimum focusing distance (only 28cm), and was gone by the time the focus was wound round to 50cm. Looking forward to using this "in the field"!
  • gerry
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    by gerry » Fri Apr 27, 2012 8:30 pm

    Nice one Beeb.
    What material did you use for the CPL holder? looks like black nylon or something.
    just coz its the internet does not mean you can act like a dick :)
  • W G
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    by W G » Fri Apr 27, 2012 10:44 pm

    Great application of craft Beeb but what would possess anyone to buy a good lens and then put a Cokin filter on the front of it?

    In the film days I had hundreds and hundreds of dollars worth of filters - especially grads and polarisers - and used them constantly. When I went digital I bought a Circular Polarising filter and a UV filter in the two sizes I needed for my lenses. It is that long since I used the UVs I don't even know where they are any more and the Polas hardly ever get a run unless I want to see through water in a swimming pool to show tiling details for instance.

    Colour correction and balancing is far more facile in post-processing ..... and probably more accurate and localised.

    Cheers,
    Walter Glover

    "Photography was not a bastard left by science on the doorstep of art, but a legitimate child of the Western pictorial tradition." —Robert Galassi
  • beeb
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    by beeb » Sat Apr 28, 2012 12:01 am

    Thanks guys.

    gerry wrote:Nice one Beeb.
    What material did you use for the CPL holder? looks like black nylon or something.


    The holder is machined from aluminium alloy - 2024-T3 to be exact. It's a bit of a softer grade than ideal (5056 or 6064 would have been preferable), but it shouldn't really have any negatives as the item will not be exposed to heavy loads or any abrasives (well, hopefully not! :lol:) - It was then hard anodised black (which hardens the outside of the item and adds corrosion and wear resistance).

    W G wrote:Great application of craft Beeb but what would possess anyone to buy a good lens and then put a Cokin filter on the front of it?

    In the film days I had hundreds and hundreds of dollars worth of filters - especially grads and polarisers - and used them constantly. When I went digital I bought a Circular Polarising filter and a UV filter in the two sizes I needed for my lenses. It is that long since I used the UVs I don't even know where they are any more and the Polas hardly ever get a run unless I want to see through water in a swimming pool to show tiling details for instance.

    Colour correction and balancing is far more facile in post-processing ..... and probably more accurate and localised.

    Cheers,


    Haha, their CPL's are actually quite good (well to me at least...). Ever-so slight brownish cast, but not enough to be any issue at all. For ND and ND-Grads I use Lee resin filters, which are excellent for my purposes. Basically no colour-cast, and don't seem to have any other detriment on the image (The Cokins were another matter altogether though, colour cast and slight loss of sharpness, and the HiTech filters I tried are far, far worse - horrible blotchy flaring nightmare they were...)

    As I shoot mainly outdoors/landscapes - the CPL is a huge benefit to me. While colour can be 'recreated' in post-processing - being able to clearly define the bubbles and foam on the surface of a rainforest stream, showing the the depth and colour present beneath the surface reflection, adjusting the reflections coming off rocks or even just to show the true colour of trees or ferns without any adjustments in post makes it a go-to item for me.

    For reference - The girlfriend has one of the very high-quality Hoya CPLs, and in my opinion I prefer the Cokin. The Hoya produces a much more mild effect than the Cokin, and otherwise the image quality is comparable.
  • gerry
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    by gerry » Sat Apr 28, 2012 12:08 am

    2024-T3 - lol.. you must be in aviation - anodising too, now we are talking.
    just coz its the internet does not mean you can act like a dick :)
  • beeb
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    by beeb » Sat Apr 28, 2012 10:33 am

    gerry wrote:2024-T3 - lol.. you must be in aviation - anodising too, now we are talking.


    Haha, yep. But I swear I bought the material at Bunnings, lol... :wink: :lol:

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