Light Meter Calibration

[Arklatexian]

There are a ton of problems when it comes to measuring light. First off, an artificial light source will always be nonlinear across the spectrum. Even two light sources of the same color temperature manufactured from different technologies will produce different results across the spectrum. Add to that the fact that our commercial light meters don't actually measure light. They measure electricity that's influenced by light (using a photovoltaic, photoresistor, or photodiode), and there is no good way to turn pure light into pure electricity. So coming up with a circuit that can measure light at all colors and levels accurately is impossible in a hand held device with our current technology. Besides that, film itself doesn't have a linear response. And if you want to get even further into the weeds, your shutter, aperture, and film speed are almost certainly off. I've never seen a shutter, electronic, pneumatic, or mechanical, that was dead on at all speeds. And if you take the time to measure and calculate your lens's aperture settings, you'll probably notice most of them vary a bit from their marked settings.

So it's foolhardy to worry about absolute values, unless you only plan to take the same photograph under the same conditions for the rest of your life. What's important is finding a workable process that allows you to make good photos, and accept small variations as inevitable without compromising your artistic goals.

I have a bunch of light meters, and most all of them are off by a stop or more. They're still usable because I'm familiar with them and know how to use them to get a usable reading. I understand each ones strengths and limitations. As long as you can get a good photograph from one, that's all that matters.

Had a friend once who went overboard on things that he could measure and control. Example: when he built his darkroom, he had a drilling contractor drill a hole down to bed-rock, set pipe and fill that pipe with concrete. After the darkroom was finished, he put a table and his enlarger on the pipe which was isolated from the rest of the room, all to control vibration. He had a pre WW2 Zeiss Contax rangefinder with three lenses. Shortly after buying the kit, he measured the apertures of all three lenses. All three were off 1/10 of an f stop. He returned the equipment to Zeiss, They too measured the aperatures, found he was correct, and re-marked the f stops to accurately show the new stops. When he died his family had the camera store where I worked sell his photo estate and I had a good look at the lenses. You could see where Zeiss made the changes. I wonder how he would have calibrated a meter.......Regards!......(We often wondered what would happen if there was an earthquake in California or Japan while he was trying to print)

 

[Bill Burk]

Had a friend once who went overboard on things that he could measure and control. Example: when he built his darkroom, he had a drilling contractor drill a hole down to bed-rock, set pipe and fill that pipe with concrete. After the darkroom was finished, he put a table and his enlarger on the pipe which was isolated from the rest of the room, all to control vibration. He had a pre WW2 Zeiss Contax rangefinder with three lenses. Shortly after buying the kit, he measured the apertures of all three lenses. All three were off 1/10 of an f stop. He returned the equipment to Zeiss, They too measured the aperatures, found he was correct, and re-marked the f stops to accurately show the new stops. When he died his family had the camera store where I worked sell his photo estate and I had a good look at the lenses. You could see where Zeiss made the changes. I wonder how he would have calibrated a meter.......Regards!......(We often wondered what would happen if there was an earthquake in California or Japan while he was trying to print)

Funniest story I read tonight thanks. I could just imagine what your friend would have contributed here.

 

[wiltw]

.(We often wondered what would happen if there was an earthquake in California or Japan while he was trying to print)

Silly question...minor tremors happen all the time in CA. So someone so obsessive can simply install a seismograph, then consult it a moment before actuating the enlarger timer, and delay a few moments if one is mid-tremor above Richter 3.0

I chuckle at those who fear living in 'earthquake country'...the annual fatality rate is far below the annual fatality rate from earthquakes and tornadoes. But it serves us well to keep the CA population growth just a bit less frenetic.

 

[Bill Burk]

The guy who lived across the street from me works for the USGS. Pete showed me the map marking our area in yellow (severe shaking). Just before he moved to a hilltop property on bedrock.

 

[dmr]

he had a drilling contractor drill a hole down to bed-rock, set pipe and fill that pipe with concrete. After the darkroom was finished, he put a table and his enlarger on the pipe which was isolated from the rest of the room, all to control vibration.

LOL, I'm not a civil engineer by any means, but I would think this is an excellent means to effectively transfer the slightest seismic tremor directly to the enlarging table.