a Cokin X-Pro filter on the Sigma 12-24 lens
I first discovered how to fit Cokin P-series filters onto my Sigma
12-24 EX DG lens I have upgraded to a Canon EOS 5D, a camera with
a full-frame 24x36mm sensor, which makes this lens really wide.
However, there is no way that P-series filters are large enough.
I spent a while using Lee 100mm filters, following a suggestion
from a fellow 5D/12-24 user, Gareth Cooper, but was still restricted
to using the lens in the 20-24mm range.
page shows how, after considerable experimentation, I managed to
get a Cokin X-pro filter mounted in such a manner that it can be
used on a full-frame camera, such as the Canon EOS 1DS or 5D - or,
even, a film camera. Also, fitting Lee 100mm filters to the same
I can now use them down to about 16-17mm full-frame or the full
12mm on a 1.6x cropped sensor camera.
I bought a replacement Front Cap Adapter, product code 512520, from
Sigma Imaging (UK) Ltd. As at Jan 2006 the price was £19.99
including postage. Once it had arrived, the butchery began.
I cut off the front of the adapter - using a hacksaw I cut along
the line of the front one of the three grooves on the outside of
the adapter. This lines up with just inside the front strip of felt
on the inside of the ring. Once deburred this allows the ring to
slide right back on the lens. The protoype involved simply filing
the inside lip off the adapter but this was unsatisfactory as it
was impossible to avoid some damage to the felt lining and made
it a poor fit on the lens.
put a lip on the outside of the front edge, just small enough for
the Lee standard filter holder to fit on and lock onto what is now
the front groove on the sleeve. This lip was made from a ring of
plastikard, backed with epoxy resin. Putting a sheet of plastic
onto the Lee holder between the body and the filter guides with
an appropriate sized hole ensures that the holder cannot slip too
far back whilst the lip on the sleeve prevents it coming off on
I glued four short strips of plastic to the sleeve barrel at 90
degree intervals, with a 5mm gap between them and the aforementioned
lip. These will hold the X-Pro adapter in place.
image shows the modified sleeve, with both the lip and the plastic
this one shows the sleeve on the lens. It is slipped right back
so that the front edge is level with the lowest points of the petal
used with the Lee holder it will not be necessary to slip it so
far back but for the X-Pro it is essential
I made up a frame with a hole the right diameter to fit on the sleeve
and cutouts at the 45 degree points to correspond with the lugs
on the sleeve. On the extremities of the wings I built up blocks
to which the armas of the holder will be mounted. I decided to make
the arms detachable as the whole assembly wil be some 150 x 225
mm in size, a problem to store in the camera bag as one unit. The
outside faces of the mounting blocks are 148mm apart. The mounting
hole is lined with several layers of plastic to bring it up to just
under 5mm and make it a good fit on the sleeve, whilst the edges
of the frame are lines with more plastic to provide stiffening.
following photos show the front and back views of the frame.
next task was to make two arms to hold the filter. these are a box
construction for stiffness and slot over the mounting blocks on
the frame, fixed in place using two spare tripod mount thumbscrews
I happened to have lying around. The threads in the mounting blocks
are a couple of 3/8"-1/4" adapter that I also happened
arms of the holder are 225mm long and the top faces stand 14mm proud
of the front edge of the sleeve when the holder is mounted on it.
The inside faces of the arms are 128mm apart when the whole frame
the very ends of the arms I then fixed a set of Lee filter guides
(one guide only), with a "pad" of plastic underneath to
make the lower surface of the guides. The inner edges of the guides
are 120mm apart which allows a slight "slop" for the filter
that I received which turned out to be 128mm wide instead of the
nominal 130mm, and the inside spacing from bottom to top of the
guides is 3.5mm to accommodate the thickness of the filter. The
inside upper edge of the arm assemblies and the inner ends of the
filter guides are bevelled to ensure that they don't appear in the
image area under any circumstances - the amount of bevel was determined
by trial and error on the camera.
we see the filter holder assembled;
here it is mounted on the lens, without and with a filter in place;
the construction was completed and I was testing it I found that
it was possible for light to reflect off the back of the filter
onto the front of the lens in some circumstances, so I made up two
sheets of plastic which can be slipped into guides on the back of
the frame when required, as seen here;
final pic shows the side elevation of the completed filter holder
mounted on the lens, it's a big beastie but I'm looking forward
to using it ;-)
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text and photos are copyright © Chris Maddock, 2006