P3D Re: Cokin Filters

[Tom Deering <tmd@xxxxxxxxxxx>]

>With all this talk of filters I'm wondering if anyone has any hands-on time
>with the big Cokin filters (X-Pro?).  They measure close to 5"x7" (yes,
>inches, not cm) and so one filter could probably cover both lenses and the
>viewfinder of most stereo cameras...if you can figure out how fit the
>holder.

I'm not familiar with Cokin filters that big.  It kind of seems like 
overkill to use such a large filter, since it only needs to cover a 
pair of lenses the size of a nickle.

Instead, you can use the much smaller and (I assume) cheaper "P" 
series if you are willing to cut them in half.  They measure 83 mm 
wide, so each half is plenty big to cover your lens.  I cut mine down 
the middle, centered each half over a lens, and cemented clear 
plexiglas to fill the gap between.

This is really simple to do, and quick.  I made four in about 30 
minutes. One good thing: the plexiglas gives you a handle to grab the 
thing by, keeping your fingerprints off the filter.  Since the filter 
is just soft plastic, they don't take well to repeated cleaning.

For me, the most useful filters are the G1 and T1 gradual filters, as 
well as the Sunset 1 and 2.  These are all graduated filters, with 
the top half darker than the bottom half.  There is a graduated 
transition in the middle.  I especially like the G1, which is neutral 
grey.  They let you darken a bright sky to fit within the response 
curve of slide film.

You need to mark the transition for your viewfinder, or you won't 
know where the effect will end up on your photo.  (Usually you line 
up the transition with the horizon.) I placed a horizontal mark on 
the plexiglas at the right point.

The filter holder is simple enough.  I made mine out of Plastruct, 
which is grey ABS model-making plastic.  Any good hobby store has it. 
I used the kind that is supposed to be a tiny "I-beam".  The channel 
is exactly the right size.  Stick the finished holder to your camera 
with double-sided foam tape.  You may need to dremel out holes for 
the cable release, etc, but that's easy.

The "P" series gradient filters are about $15 from B&H.

I've never seen anybody else do this.  If anybody wins a big prize 
using this idea, I want credit.  :^)

Cheers,

Tom Deering