Re: filters in front of the film plane...

[Tom <chowt@xxxxxxxxxxxxxxxxxxx>]

Hi

On Mon, 22 Sep 1996 "Willem-Jan Markerink" <w.j.markerink@xxxxx> wrote:
> 
<snip>
>
> I am close to implementing the perfect
> filter solution for an SLR....mounting a filter between the film
> rails. The honor for this solution goes to Andy Davidhazy, since I
> first read about it in one of his IR-FAQ's. Obviously,
> gelatine/polyester is too fragile for this application (not per se,
> but with darkloading it definately is), and normal glass/resin
> filters are to thick (and hard to cut). But a few days ago I
> received #87C in a different material from my manufacturer; thin,
> flexible, easy to cut, yet far less fragile than gelatine/polyester.

There are a few things that you should consider about puting a filter
directly in front of the film plane. This filter will have to be very
clean and abberation free. Any dust, lint or optical abberations on the
filter will show up clearly on the negative due to the close proximity to
the image plane, then magnified when you enlarge. One of the big
advantages about placing filters in front of the lens is that these things
simply disappear. 

One solution is to place the filter diagonally in the mirror box below the
mirror, distancing it from the film plane. (like a pellicule mirror
system) You guys with the fancy autofocus stuff would have a problem with
the sub-mirror. 

> 
> Although I intended to use this material for flash applications (as I
> said in earlier postings), the actual between-the-film-rail solution
> was provoked by my fisheye lenses; the Russky 16/2.8 has rear screw
> filters, the Sigma 8/4 uses internal screw filters. Both are a rather
> odd filter size, and require very thin glass as well; no such thing
> from any filter manufacturer. So I needed a homebrew solution....but
> that would still require a lot of hassle in changing the filter
> between composing/focusing and the actual exposure. I also pondered
> about using one of these spy-glass contraptions that are used in
> doors, as a 180 degree viewfinder, but mounting a filter behind the
> mirror, between the film rails seems an even better way to go with
> this new #87C material.
> 
> The only thing I need now is an absolutely clean type of tape, so
> that I can remove it without leaving a sticky substance inside the
> camera....8-))

I've never has problems removing tape residue using fresh sticky tape. 
Ofcourse tape that does not leave a residue is better. Better yet, use a 
simple mechanical clip system to hold the filter in place...

Cheers,

Tom

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Topic No. 6