From:             "Willem-Jan Markerink" 
To:               infrared@a1.nl
Date sent:        Fri, 11 Sep 1998 12:28:54 +0000
Subject:          Re: Filters
Send reply to:    infrared@a1.nl

On 10 Sep 98 at 17:43, James Lewis wrote:

> I've tried 87 and discovered I prefer the 25. IR effect is more pleasing with the
> 25. And you don't have to shoot blind. (The 87 passes NO visible light. It's like
> a piece of black glass.)

That is why the BTFR (between the film rails) filter solution is so cool:

Pro:
- no viewfinder darkening/blackout (would even apply to the 
non-opaque #25/70/89B)
- no more endless switching of filters between composing and exposure
- no more switching of filters while swapping lenses
- all strange filter constructions are solved (my Sigma 8mm uses 
internal filters, requiring to split front and rear of the 
lens(!)....same would apply to rear-slot high end teles, as those want 
to be focused with at least a clear filter mounted
- add my addiction to shoot in very hostile environments (steep ski 
slopes, -20C and a wind speed that topples you over), and any bare 
finger fiddling with filters is a night mare.

Contra:
- it requires a dedicated IR body, as the filter is semi-permanently 
mounted (clear office tape in my case, nothing exotic nor damaging)
- not all cameras have tall enough film rails to accept the most 
sturdy quality (0.4mm thick #87C)

- only #87C (0.4mm or 0.1mm), #87, #12 and #29 (only 0.1mm) are 
available in polyester, other colors only exist in gelatine (more 
sensitive to moisture, scratches and fingerprints, and cannot be 
cleaned, in all aspects unlike polyester)[*]

Practical: I have one (#87C/0.4mm) permanently mounted in one of my
EOS-1's, for nearly 2 years now. Still as good as day one. 

As for the filter color itself: the #25 doesn't give me the unwordly
effects I want/like....but that's a personal choice, also depending
on subject I guess (portrait/nude vs landscape/architecture).

Last winter I even sacrificed another EOS-1 for EIR with a
permanently mounted #12....the swapping of various lenses over 3
bodies (HIE, EIR, normal color) is as foolproof as can be....totally
impossible to forget a filter, or use the wrong one (don't laugh, has
happened to me several times in the past, these hostile environments
don't allow much time for thinking).

I once started this concept when dealing with the 8mm/f4.0 Sigma circular
fisheye....even though it has internal filters (old version) or rear slot 
filters (new version), it still leaves you with the problem of blacking 
out the viewfinder, without quick access to the filter (as with 
front-mounted filters, even though that is clumsy on itself too 
(tripod!)).


[*] note that even though Kodak/Wratten doesn't make all intermediate 
colors any more (only #70, #87 and #87C I believe), but I can still 
supply any possible color in gelatine (different manufacturer) for 
those who need this type of material/solution

All qualities polyester (12/25/29/89B/87/87C) are US$0.50 pro square
centimeter, same thing for all gelatine colors. This equals US$3.50 pro 
square inch, or US$12.50 for a piece of 5x5cm, out of which you can cut 
two BTFR-filters (24.0 x 45mm).

Send me private email for details on ordering.
 


--                 
Bye,

Willem-Jan Markerink


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



[note: 'a-one' & 'en-el'!]

If you have any question, remark, comment, want to share some philosophy or just want to express your opinion about these pages, feel free to send email to: w.j.markerink @ a1.nl