Re: Filters!?!?

[Eckhard Stephan <eckhard.stephan@xxxxxxxxxxx>]

>Are the differences significant? Cause what I really want is to explore that absence >of depth of field that I see in some IR photos.
>
>Best regards,
>PedroL

Hello Pedro,

the differences between a Wratten #25 or #29 (dark red filters, which
are also used for normal bw photography) and visually opaque "IR"
filters such as the Wratten #87 or #87C are visible, but not too strong.
With a Wratten #25, Kodak HIE as well as Konica IR will exhibit all the
characteristic traits of IR films like white trees, dark skies,... With
a #87 these effects will still increase, besides that contrast will in
general get higher. But these are rather minor differences... So there's
no need to buy an expensive (and not readily available) opaque IR filter
right now.

I am not sure, what you mean by "absence of depth of field". In IR
photography - like in "normal" photography - depth of field is
controlled by your aperture setting. Small apertures (f22, f16) = large
depth of field, large apertures (f 2,8, f4) = little depth of field. In
some cases problems might occur with IR films, because IR light focuses
on a slightly different plain than visible light. As long as you are
using wideangle or standard lenses and not too large apertures, you can
practically neglect this effect. You might however (seldom !) get some
trouble with tele or macro lenses, which generally offer comparatively
little depth of field. 
So what can you do about it? When using Kodak HIE with a Wratten #25 or
some other red filter you can still see through, I would not bother
about focus corrections for IR at all, no matter what kind of lenses you
are using. With visually opaque filters I would advise you to use the IR
correction marks (red dot or "R") on your lenses, if there are any. If
not, just focus for the visible light and use the  smallest aperture
possible. I've shot quite a lot of pictures through a #87 with an
automatic camera, where nor Ir focus corrections are possible. Never had
any serious difficulties... ;-)

Happy photohgraphing,

Eckhard 
-- 
========================================
*          Eckhard Stephan             * 
*          Freiburg (Germany)          *
*     eckhard.stephan@xxxxxxxxxxx      *	
*   http://www.eckhards-photobox.de    *   
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