For those folks who are uncertain which filter to use, here are spectral graphs for various filters.
A filters effect on the photographic negative depends heavily on the type of film you're shooting.
In other words... the emulsion's spectral sensitivity should be taken into consideration when selecting a filter.
This is especially true when using non-panchromatic films (x-ray, Infrared, Ortho, collodion, etc.).
Consult your films data sheet for it's spectral response curve and compare it to each filters curve.
The heavy dark line is the filters transmission drawn on a 360-750nm colored background.
Panchromatic films are more sensitive in the central portion of the graph.
It's here where most contrast filters are used (Yellow-green/ Orange/Red).
If you're shooting paper negatives, the Blue/Green part of the graph is most important.
Single grade photo papers are mostly Blue sensitive.
VC papers have added green sensitivity.
Orange/Red filters are nothing more than safelights in this case.
The dashed line represents the spectral response for Ilford's Ortho Plus film.
Ortho films can only see Blue/Green light... so Yellow/Red filters are mostly useless.
The 380-520nm outlined area defines the spectral response for typical wet plate (collodion) emulsions.
A Blue filter may make focusing easier by blocking out the distracting Yellow/Red component.
Reinhold
www.re-inventedPhotoEquip.com
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