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Ron_g
Tinkerer
Username: Ron_g
Post Number: 19
Registered: 07-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, May 04, 2010 - 10:12 am: | 
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This is something that would benefit a lot of us and has been referenced many times by many authors over the years.
We need something of an industry standard that we can use to calibrate our meters with that will remain a constant throughout the world within reach of the common man,that is it should not cost so much that we cannot afford it,we have those now but I don't know what they are for sure.
I don't have any constructive ideas as yet because I have not thought seriously about it.I have some fairly reliable test equipment but need some ideas to work with.
What can we come up with,let's hear it,the simplest things are often the best.Ron G |
Tom_cheshire
Tinkerer
Username: Tom_cheshire
Post Number: 307
Registered: 04-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, May 04, 2010 - 10:42 am: |
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60 Watt incandescent lightbulb at 6 feet (2 metres) distance? |
Djamorpheus
Tinkerer
Username: Djamorpheus
Post Number: 40
Registered: 10-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, May 04, 2010 - 03:53 pm: |
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sunny 16? |
Monopix
Tinkerer
Username: Monopix
Post Number: 128
Registered: 11-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, May 05, 2010 - 08:36 am: |
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Yes, I was going to say the sun as well. Probably the only light source that meets the criteria ("will remain a constant throughout the world within reach of the common man,that is it should not cost so much that we cannot afford it").
Problem with any mains driven light source is that mains electricity varies and so the output wouldn't be constant. Also, two lamps equally rated from different manufacturers won't necessarily give the same light output (the wattage is a power consumption not a light output measure). Incandescent lamps are not usually balanced for daylight either and this can cause different readings with different meters dependant on what type of sensor they are using.
I don't think it's an issue though. I always compare meters with a known good one. There are potential problems with this as well like different acceptance angles but I try to compare two cameras of same make with the same lens attached to minimise differences.
This also raises the issue of how accurate do we need to be when calibrating meters? I don't think I've ever seen a spec. from a manufacturer as to accuracy so what are we aiming for? I guess most film cameras are used with negative material so slight errors shouldn't be a problem and anyone who uses an old camera with reversal material should be working out their own EI anyway.
So, sounds like a good idea but I'm not sure of the benefit. A daylight balanced, variable light source could be useful for checking meters but I don't think it needs to be calibrated - just compare the readings with a known good meter. |
