Re: Filter questions

[Clive Warren <Clive.Warren@xxxxxxxxxxxxxx>]

At 8:35 pm -0600 24/2/01, Keith Zimmerman wrote:
>
>I'm planning for the up-coming release of this year's Konica by increasing
>my tool inventory of filters.  I have a couple of quick questions.
>
>1.  Can someone discuss the optical pros and cons of the various materials;
>polyester, gelatin, resin, and glass.
>
>2.  Is there a site anywhere that has this type of information?
>
>3.  Which material works best?  Or are there instances when one material is
>better suited than another?
>
>4.  Which filters would be candidates for inclusion in my new IR toolbox?  I
>currently own a 25.
>
>Hopefully, this information will allow me to make a more informed decision
>on the type of filters to buy.  Thanks in advance.

Will try to answer your questions.

1. Polyester scratches easily and is probably not as good optically 
as, say resin - particularly after it has a few scratches.... Gelatin 
is good but fragile and difficult to mount. Glass is usually a 
sandwich - glass-filter material-glass.  That adds a lot of surfaces 
for light to be refracted and invariably these are not coated. Resin 
(personal favourite) is optically very good as it is the same 
material as used in lenses for some elements which are too expensive 
or difficult to grind using glass.

2. The (wait for it!) Infrared FAQ addresses some of the issues you 
raise - http://www.infraredfaq.org

3. There are a number of issues here - if you use filter holders and 
are comfortable with them then in my not very humble opinion resin is 
the way forwards :-)  There is a discussion in the IR FAQ.

If you are using an SLR and don't want to lift filters for 
view/composition then a behind the film rails polyester filter is an 
option.  WJ is the person to contact about that.

4. The 89B is a good catch all - works well with most IR films - 
again there is a section in the FAQ called, surprisingly, "Which 
infrared filters?".

Hope this helps,

-- 
All the best,

              Clive   http://www.cocam.co.uk
                      Photographic Services, Filters and Equipment, Infrared FAQ
			http://www.f32.net
			Large Format Travel and Stock Photography
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