Re: Metering question

[Tom Purdum <javaboyone@xxxxxxxxx>]

Clive,

Thanks for the response.  It is all becoming clear
now.  I rated the film at about 3ASA.  It was a guess
as my gosen meter does not go that low.  I was
shooting with an 87 filter.
--- Clive Warren <Clive.Warren@xxxxxxxxxxxxxx> wrote:
> At 9:03 pm -0400 12/7/00, Michael Kennedy wrote:
> 
> >I haven't shot many rolls of Konica 750--but the
> lab I worked in process
> >about ten for a photographer and they all came out
> blank. My understanding
> >of some filters are that they pretty much cut out
> all light below 800nm.
> >Konica has peak sensitivity at 750(hence the name).
> Shooting with opaque
> >filters is just about the same as shooting with
> your metal lens cap on.
> 
> There are quite a few of us Konica users on the list
> who shoot 750IR with
> 89B and 88A filters.  Whilst these filters are not
> completely opaque, there
> is not much visible light allowed through.
> 
> If you have a quick look at the film sensitivity
> curves in the Infrared FAQ
> (URL in sig. file) (Section 12 "Which Infrared
> Filters"), it is clear that
> Konica 75IR is sensitive to light from 640 to 820 nm
> in addition to the
> intrinsic  sensitivity range of AgBr 400 to 500nm.
> The peak sensitivity is
> of course 750nm in the infrared range.
> 
> Generally, filters also have a sensitivity curve
> rather than a "cut-off".
> So, again looking at the sensitivity curves this
> time for filters to
> Wratten specifications, even an 87C will allow some
> infrared exposure on
> Konica 750.
> 
> The exposures required for the more opaque filters
> will be a lot longer -
> see Section 13 "Exposing - Film Speeds and Rating
> for Filters".  I have not
> listed exposure times for Konica 750 for filters
> above the 89B as the film
> would have to be rated at ridiculously slow speeds. 
> However I have shot
> Konica 750 using 88A filters as an experiment.
> 
> Essentially when using increasingly opaque filters,
> film speed decreases
> and the contrast is increased in an already high
> contrast film making it a
> bit of a challenge to print.
> 
> If the photographer you refer to was using say an 87
> or 87C filter and
> rated his film higher than 1ASA then blank film (ie
> underexposed) would be
> the result.
> 
> It's all in the FAQ :-)
> 
> There are some peops on the list who do shoot Konica
> 750 using 87 filters -
> never let the rules stop you experimenting; it's
> useful to know the
> technical limits when playing around though.......
> 
> 
> 
> 
> All the best,
> 
>              Clive   http://www.cocam.co.uk
>                      Photographic Services, Filters
> and Equipment, Infrared FAQ
> 
> 
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