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Old 11th October 2008, 04:01 PM
Les Meehan Les Meehan is offline
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Default Of course filter factors don't work!

Filter factors don't work except when the colour temperature of the lighting matches that of the 'standard' used to determine the factor. Which in real terms means hardly ever!

Thus, a red filter used near sunset WON'T darken the blue of the sky in the way you might expect and the factor will usually over-expose your negative.

Discuss.
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Old 11th October 2008, 07:16 PM
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So what does work?
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Old 11th October 2008, 11:40 PM
Les Meehan Les Meehan is offline
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Ah, taken the bait I see! Percepts, I know you know things (or as the boy in the film says 'see things').

What works? Hmm, one of the dilemmas of our exposure meters. Remember Fred Picker? He, with the help of a scientist (name not recalled, Paul Horowitz?), tried to make an exposure meter with a colour sensitivity equal to panchromatic film (actually Kodak Tri-X which at the time was Fred's preferred film). This allowed one to meter through the filter to ascertain the actual changes made by the filter to the image tones when using Tri-X (what a great film!).

I have one and it works very well; a Modified Pentax 1 degree digital spot meter.

Of course, different films have slightly (or dramatically depending on your point of reference) different colour response even though they all claim to be 'panchromatic'. So, the Modified Pentax from Zone VI may or may not exactly match a particular film BUT it does put one firmly in the ball park when using contrast filters.

Meter through the filter in any light and you can determine what the filter is actually doing to the subject values, something not possible with only filter factors. Also, you obtain an accurate exposure in any lighting conditions.

Oh that meter manufacturers paid so much attention to the issue!!!

Discuss...
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Old 14th October 2008, 01:37 PM
Dave miller Dave miller is offline
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This seems to suggest, bracket and then bracket some more, or is it an advert for a Pickermeter?
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Old 14th October 2008, 02:49 PM
Les Meehan Les Meehan is offline
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Quote:
Originally Posted by Dave View Post
This seems to suggest, bracket and then bracket some more, or is it an advert for a Pickermeter?
Not an advert, simply discussing one of those aspects of BW photography that the 'big' manufacturers haven't bothered to deal with.

How about a light meter designed so that you can input to it the spectral response curve of the film in use and it automatically changes it's spectral response to match that film (rather like colour profiles in digital or how some DSLRs have programs designed to emulate various mono films). Now that would be a useful light meter!

Without the spectral response of the film and meter matching it is actually probably near impossible to trully 'visualise' the negative densities. Fortunately, Nature doesn't usually produce too many really saturated colours so the spectral response differences between film and meter are acceptable on a daily basis (however this doesn't answer the filter factor issue which I feel the Picker modified Pentax at least went some way towards).

Or are they...
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Old 14th October 2008, 03:26 PM
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Paul Butzi has compared his modified and unmodified Pentaxes and was not impressed (http://www.butzi.net/articles/zone%2...worth%20it.htm) - also see his update link in that article which reinforces his conclusion.

Interestingly (for me) he also compares the Pentax with the Sekonic L-508 (the previous model of my meter) with the conclusion that they both match exposures very closely (< 1/6th stop) with the exception that the L-508 consistently reads 1/3rd of a stop higher (this seems typical of Sekonic meters in general from what I have read - they appear to be calibrated to a different standard than the usual 18% reflectance).
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Old 14th October 2008, 09:25 PM
Les Meehan Les Meehan is offline
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Thanks for the links Bob, I have read through all Paul Butzi tests and results with interest.

When I first bought my Modified Pentax back in 1991, I wanted to prove to myself that I had actually got something 'better' and so conducted similar tests myself. At the time I also had a Soligor one degree meter which I was replacing with the Pentax. So I did both a linearity test and a colour sensitivity test. I normally read about things and then if they interest me make tests to convince myself a procedure or piece of kit is in deed 'better' than my existing things before adopting or rejecting the new thing (something I always say to people I teach is "don't take my word for anything, test it for yourself and then decide").
I think I still have the negs from those tests. To make my colour test 'practical', instead of using a colour test chart as Butzi does I simply used my colour contrast filters with a daylight balanced light box. My thinking being that I don't shoot test targets but I do want to know if I can meter through my filters on a given subject.
My results conflicted with Butzi. I did actually find that the Modified Pentax did indeed produce the same neg density (or within a nat's widget) when I exposed the light box to zone V without filters (as the 'standard') and then, using each of Red, Green, Yellow and Orange filters, again made a zone V exposure metering through the filter. The same test was done with the Soligor and also with the TTL of my Canon A1 camera. The Pentax was the only one that produced consistent densities. The others were all over the place.

I will try to find those test negs and post them here.

Personally, I don't like Picker bashing (or Adams bashing etc), which usually occur after the person has passed and so cannot defend their position. I think Zone VI under Picker produced some excellent items and solved some issues. My Zone VI cold light head for the Beseler for example, prior to which I couldn't get consistent consecutive exposures. That cold light sensor and timer is great.

Sure, Picker was a bit too loose with his marketing blurb and some of his claims have since been shown to be incorrect as Butzi points out but not everything was bad (I love my Zone VI 5x4 in American black walnut made by them, a masterpiece by any standard).

The simple thing would be for everyone to test their own meters and then judge. Maybe this group could organise a big test?
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