Re: Question about EIR

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On  8 Jun 00 at 4:34, George L Smyth wrote:

> --- Bertha Adamson <badamson@xxxxxxxxxxxxx> wrote:
> > Bert P. Krages wrote:
> > 
> > No one else has mentioned this, so it made me wonder - is the focusing
> > difference of IR versus visible light not an issue with color IR? Do you not
> > have to adjust focus on some lenses as you would with B&W IR?
> 
> One should not be correcting the focus when using EIR, as you would do with
> HIE.

This is more like "you should, but you can't".

You should correct for IR, but you can't because that throws visible 
focus off....unlike HIE, EIR requires nearly the entire light 
spectrum (yellow to infrared), not just a deep-red/infrared slice of 
the spectrum (like HIE). 

Only alternative for this dilemma is either a highly-corrected (APO) lens, 
or stopping down....shooting wide-open with (non-corrected) tele's is 
a compromise in image quality....either visible is unsharp, or 
infrared....
Note that this sharpness degradation might be hard to spot, but it 
definately is a factor in creating the perfect EIR image, especially 
with tele's.

A similar recommendation for APO lenses with IE/EIR can also be
found in Guenter Spitzing's book "UV- und Infrarot-Fotografie".

--                 
Bye,

Willem-Jan Markerink

      The desire to understand 
is sometimes far less intelligent than
     the inability to understand

<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]
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