Sam/Rok 7.5mm filter adapter

Discussion in 'Native Lenses' started by letsgofishing, Jan 29, 2014.

  1. letsgofishing

    letsgofishing Mu-43 Veteran

    Nov 21, 2012
    South Africa
    Mike Kaplan
    I'm predominantly a seascape photographer and love the FOV the little Rok gives - however, I was very frustrated by the inability of the lens to accept filters.

    So I did few drawings and discovered that - fortuitously, the 62 mm ND filters that I use on my 12-40 were a bit larger than the outside diameter of the front of the Rok.

    Went of to see an engineering friend of mine along with a bar of 70mm dia. aluminium. He first mounted the lens in his lathe and machined the 2 longer petals of the built-in lens hood to the same height as the 2 shorter ones. He then machined me 2 beautiful little rings from the ally bar that are a push fit over the front on the Rok. Then cut a thread that is the same size as the thread on the FRONT of the ND filters - you got any idea how fine this thread is??? - this man is an engineering marvel!!!

    Push-fitted the ring over the front of the Rok - reversed the filter and screwed it on - works perfectly but with one small (not for me) problem - due to the depth (thickness) of the filter, if you shoot in 4:3 or 3:2 format, you can see the filter in the 4 corners. However, shooting landscapes like I do, I use 16:9 and only a bit of the filter is visible - see attached image.

    Just thought I'd pass this on to those of you who want to use ND (or other filters)


    • Like Like x 4
  2. Jaynometry

    Jaynometry Mu-43 Regular

    Sep 13, 2011
    Toronto, Ontario
    I got way too excited when I saw the subject line for this thread and it broke my heart that it's a one-off piece haha. I, too, love ND filters and would love something like this. Great job!
  3. ahinesdesign

    ahinesdesign Mu-43 Top Veteran

    Dec 6, 2011
    NC, USA
    I've often wondered if the Panasonic 8mm filter holder would fit the back of the 7.5 like it does on the 7-14mm. This places the filter (gel type) on the back of the lens, which would eliminate the vignette...

    Even with the 7.5 set at f/22 I can't get a shutter speed slow enough for decent long exposures unless its completely dark...
  4. fmfche

    fmfche Mu-43 Regular

    Mar 31, 2013
    I'm going to look at my lens when I get home to do some measurement but my current thought is that it may be possible to mount a small diameter circular polarizer or ND on the rear of the lens. After looking at amazon it looks like 28 and 30mm diameter filters are available.

    While a polarizer on the front of a large lens would produce an uneven effect across skies and other parts of an image at the rear I believe this could be avoided.

    My main concerns on using a filter like this is that it would protrude to far into the camera and obstruct the shutter.

    If a filter itself does not fit at the very least I would think a gel could be mounted on the inside easily.
  5. pdk42

    pdk42 One of the "Eh?" team

    Jan 11, 2013
    Leamington Spa, UK
    I'd love the ability to add a big 10-stop ND to my Sammy FE too. Would be interested to hear of the rear mounting idea. I don't think fouling the shutter is a realistic risk - it's a pretty big gap between lens and the shutter.
  6. fmfche

    fmfche Mu-43 Regular

    Mar 31, 2013
    Edit: This probably won't work with circular filters no matter how small in diameter, there is too much stuff in the way such as lens contacts. Mounting a gel is probably a better way to go.

    Look like the available diameter is about 37mm. The rear element/group moves in and out so a spacer would be needed to keep it from making contact with the filter.

    I think the most secure way to do this would be to take one filter of a size that fits(less than 37mm diameter) and then glue the empty filter "holder" to the back of the lens. This way the filter intended to be used would be remove able.

    That said I'm not sure I'm about to rush out and try this as it would take 2 filters just to try out, 1 with decent threads and then a 2nd of good quality.

    I would also hate to mess up my lens or camera doing this.
  7. dwig

    dwig Mu-43 Top Veteran

    Jun 26, 2010
    Key West FL
    Moving the filter to the rear will do absolutely nothing to change the uneven skies. The skies are uneven because the the degree of polarization in the light from the sky varies with its angle to the sun.

    Light coming from the sky 90 degrees from the sun is dominantly orientated to one angle and is thus affected by the polarizer to a high degree. Light coming from the sky around the sun or 180 degrees from the sun is evenly distributed across all polarization angle and is thus unaffected by the polarizing fiter. There is no way you can reposition a polarizer to alter this bit of basic optical physics.
    • Like Like x 1
  8. fmfche

    fmfche Mu-43 Regular

    Mar 31, 2013
    Thanks for posting this, saved me a lot of headaches. Makes perfect sense. Still want to try a sort of ND setup.
  9. ajarocena

    ajarocena Mu-43 Regular

    Aug 30, 2012
    Cavite, Philippines
    best alternative is Square filters...just be patient holding it vs. exposure time settings :biggrin:
  10. pdk42

    pdk42 One of the "Eh?" team

    Jan 11, 2013
    Leamington Spa, UK
    Is there an issue with reflections off the rear of the filter if you just hold them in front of the lens?
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