[rollei_list] Re: Rollei infrarot
- From: "Eric Goldstein" <egoldste@xxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Wed, 13 Aug 2008 22:58:12 -0400
From Photonet::
Richard Fateman , Nov 17, 2001; 01:14 p.m.
(I posted this on rec.photo.medium-format, but maybe of interest here,
since it answers some questions/ poses another).
keywords: rollei infrared infrarot infra-red optical compensation macophot 820c
Does the rollei filter really have optical compensation?
I'm not sure I have the answer, but here are some tests.
The rollei infrared "infrarot" filter is described as "transmits dark
red above 700mu and infra-red with optical compensation" in the 1961
Rollei British catalog:
http://www.rkwheeldon.freeserve.co.uk/images/r12_copy.jpg
There seemed to be some question about what this meant. Or it if meant anything.
There are some claims on the web that this filter is like a heliopan
695 or wratten 89B, 0% transmission at 680nm, 50% at 720nm. This is
plausible. It is optically black, though if you view a bright light
through it, you can see a dark red image.
I set up a Rollei 3.5 Planar on a sturdy tripod, aimed at a large
aluminum construction ruler at an angle. Indoor lighting, halogen
lamps.
I took 3 pictures with macophot 820C infrared film
1. Set the focus at 3 feet (visually this was also at 3 feet from
rollei focal plane, +- an inch) and took a picture (EI 100) without a
filter. f 3.5 at 1/30 sec
2. Without changing the focus, put on the rollei (bayonet II) infrared
lens. Took a picture at EI 6. f 3.5 at 1/2 sec
3. Same as 2, but changed the focus so that the 3ft focus mark was at
the "5.6" depth of field mark. That is, I focussed closer.
The film was developed in Xtol 1+2.5 at 70F for 14 mins.
Results: photo 1 was sharpest at 3 feet: that is, the film's focus,
the viewfinder's focus, and the tape measure all agreed to within a
fraction of an inch. (I consider this to be remarkable)
photo2 was sharpest about 3/4 inch CLOSER than 3 feet.
photo3 was sharpest about 1.5 inch CLOSER.
A tentative conclusion: There IS optical compensation in the infrared
filter, because in the absence of such compensation the IR light would
be focussed best at a further distance. It is just that it appears
OVER compensated.
Perhaps the rollei filter has overcompensated at least at the 820nm
peak (?) of macophot. I haven't thought about whether this would also
be overcompensation at other focus points. Or do I have this all
backwards??
(To tell where the focus was, I looked at the markings on the ruler
and chose the point half-way between the markings that were just
getting fuzzy toward the front and just getting fuzzy toward the
back.)
Question: does this really show there is a built-in optical
compensation -- and that it overcompensates at close focus?
Richard Fateman
On 8/13/08, X.TRUONG <truongthx@xxxxxxx> wrote:
> Thanks Jim,
> So, how to used this filter. I love infrared picture!
>
>
> X.Truong
>
>
> -----Original Message-----
> From: rollei_list-bounce@xxxxxxxxxxxxx
> [mailto:rollei_list-bounce@xxxxxxxxxxxxx] On Behalf Of Jim Brick
> Sent: Thursday, August 14, 2008 4:14 AM
> To: rollei_list@xxxxxxxxxxxxx
> Subject: [rollei_list] Re: Rollei infrarot
>
>
> In a word... no. The Rollei Infrared filter is, to most visible
> wavelengths, opaque.
>
> IMHO,
>
> Jim
>
>
> On Aug 13, 2008, at 9:22 AM, X.TRUONG wrote:
>
> > Can I use it on normal BW film?
>
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