Calibrating using hot (3400K) light source?

Hi,

This one thing has bugged me for a while.<br>

Back in eighties, I read from some article about zs calibration, that if you use

tungsten light source, you should overexpose by half step (+0.5EV) in order to

get result that is usable in natural light.<br><br>

Is this true? If is, then what it is based? Is it the spectral sensivity of the

B/W films or the spectral sensivity of the light meters?<br><br>

I use Gossen Spot-master 2 light meter, and it's spectral sensivity has it's

peak around 500nm - 600nm, and is half EV less sensitive at 400nm and 700nm.<br>

The nanometer readings does not say nothing to me, in photography everything I

had read is relative to Kelvins.<br><br>

My calibration process is simple: I shoot test negatives using gray card with

black background as an target and light source is 3400K photo lamp.

<br><br>

So now I am asking what kind of light source do you use in the calibration

process?<br>

Do I have care of that 0.5EV overexposure?<br><br>

Best regards,<br>

Jukka

You are correct that the spectral sensitivity of many earlier panchromatic caused the half step

condition, not the meters. I believe most modern emulsions are not as prone to this

condition. Film data sheets will give you spectral sensitivity information. Test as you planned.

Then conduct a controlled daylight shoot and see if you need to make an adjustment.