Leica IIf light cold shoe light meter question (sorry not really a Leica question but it is Leica related)

[stvn66]

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Hi,

I have purchased a Petri light meter that I hope to use with my Leica iif.

I have attached it to a digital Nikon Z50 and set the ISO at 100 and speed at 1/100 and the aperture at f5.6 as per the meter reading.

However the manual setting on the Nikon says that at ISO 100, speed at 1/100 the aperture should be f11?

Should the readings be this far apart?

Thank you.

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[jankap]

What does the light meter see? It has a large black zoom lens in front of its nose.

The Nikon measures the light with the view of the zoom lens and from the sensor. That means - in this case - a view of 50mm averaged, in the middle enlarged or in case of spot measurement a view of 90/135mm.

The light meter possibly measures a 35mm view, that is enlarged in the middle. At least, a more or less undefined view. Whereas the Nikon gives an exact measurement.

Edited October 22, 2024 by jankap

[stvn66]

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It was sunny earler on but has since rained...after all this is the UK.

 

Edited October 22, 2024 by stvn66

[Anbaric]

Of course a meter of that vintage might be way out, but to give it a decent chance, make sure the meter in your Nikon is set to centre-weighted and not a matrix metering mode, and aim both the Nikon and the Petri meter at some neutral, evenly illuminated surface that covers the whole field of view of the lens (and yes, if a big black zoom intrudes into the field of view of the Petri this could mess with things, so also try the meter off-camera). A grey card is ideal, but you could use (say) a wall that isn't in direct sunlight. If you have another metered camera, try that too for comparison. Take the readings in quick succession and try again if the light changes.

Edited October 22, 2024 by Anbaric

[stvn66]

Brilliant, thank you.

[spydrxx]

When testing light meters I generally use a patch of solid grass filling the field of view.

[jc_braconi]

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1 hour ago, spydrxx said:

When testing light meters I generally use a patch of solid grass filling the field of view.

???

[TomB_tx]

These were Selenium cell meters (no battery) which typically do not age well. As the cell degrades they lose output, thus readings think the light is dimmer than actual, so it reads 2-stops more exposure needed than it should. It also may not have a linear response to light, so compare readings in both bright and dim scenes to see if raising the ASA setting 2 stops can compensate.

[spydrxx]

3 hours ago, jc_braconi said:

???

It approximates a grey card so great for comparison readings between 2 light meters

[bobtodrick]

19 hours ago, spydrxx said:

It approximates a grey card so great for comparison readings between 2 light meters

Pretty much everyone knew in the past that grass is very close to 18% grey reflectance.

[luigi bertolotti]

What's the approximate age of the Petri meter ?  I have a Selenium Gossen of 1974 : still reacts to light but measure is untrustable... didn't make precise evaluations, but I'd say that the error is around 2 stops (a roughly "sunny 16" situation suggests 8 )

Edited October 24, 2024 by luigi bertolotti