Re: I.R. Metering - Step up to the challenge

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

On  6 Jun 99 at 19:04, danzig@xxxxxxxxxxxxxx wrote:

> that I intend to make an IR sensitive meter.
> 
> It's irritating not being able to use convinient TTL metering for our IR 
> imagery, and modifying our camera's like W.J. pretty much 
> relegates that camera body to specifically being used for shooting 
> IR. Which is not a good idea financially for a young pro like me.
> 
> W.J. once said that he had quite simply, placed a thin red gel filter 
> *I think* in front of his Canon EOS 1's internal meter.

Nope, between the film rails.
Note that the EOS-1 has only one of its sensors in the bottom of the 
mirror box....only the spot-sensor sits there, the others are up in 
the prism.
My only argument for doing so is getting rid of all filter hassles, 
both in handling the filter and for the fact that I can't 
focus/compose through an opaque IR filter.
The only reason why you still might want to mount a filter in the 
mirrorbox itself is to cover the AF sensors, and attempt to get the 
proper IR-focus-correction that way (contrary to what most people 
believe, AF does work through opaque filters, it's just that this 
correction-aspect gives mixed results....I tested lenses that focused 
in the wrong direction).
 
> A VERY smart idea as this will filter out visible light pretty much 
> the way it does on the front of your lens, except that since this is 
> your camera meter where this is taking place so the meter will only 
> be reading the IR light falling on it for measurements for it's 
> metering recommendations.

The problem is that you need to recalibrate your internal 
meter....modern meters are quite insensitive to IR, the later the 
camera, the more pronounced. 
 
> I'm basing this last paragraph on my latest piece of equipment, the 
> Minolta 4F lightmeter, it's metering ' ball & plate ' & also the 
> recommendations I've recieved over reducing the ISO speed on the 
> meter to account for filter factor, as this is a better solution that 
> placing the filter over the measuring ' ball ' as this method 
> introduces a level of inaccuracy to your data.
> 
> Well, I suppose this IR meter will only be a reflected & spotmeter 
> type. Since as most of you know, the IR effect recorded on the film 
> is mainly due to the IR reflective properties of the object being 
> photograped.
> 
> Which would make incident metering undesirable & probably just 
> plain dumb.

On the Gossen Sixtomat Digital (the smallest digi-unit), you can 
slide a square piece of filter in the top section (where also the 
sliding dome resides). When set to 400 ASA, a piece of #87C gives 
rather consistent results compared to 1/60s @ f5.6-11.
 
> A young man who has lived 21 long years and yet still hasn't the 
> foggiest idea what life will expose him to him tommorow.    

Aha, good....so you can still be spoiled....:-))

 

--                 
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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