Exposure Meter testing any affordable devices available,or any shops still doing this

[Q.G.]

If your graph has a purpose, it's to show how extremely consistent solar lighting is!

The purpose of the graph of course is to show the (minute) variation.

As for the second, I have no idea what a "UV index" is, but it sounds like something a weather channel would cook up to scare people into putting on sunscreen.

The UV Index is indeed a medical thing, concentrating on the risk of sunburn.
But you do know that, of course.

If the purpose of showing these graphs is to show how variable sunlight is, would it not be fair to say we already know that?
The reason why it is rather variable however is not to be found in the sun itself, but in our geography and weather.
(For instance, sunlight levels tend to drop enormously when night approaches. Yet not everywhere and not always. )

 

[Ed Sukach]

"Standard Candles" - Stearin candles 3/4" diameter - used to be available through laboratory supply outfits. Burning one resulted in 1 candlepower of light. Interesting to note the variability - the light output was affected by -- the oxygen content of the ambient atmosphere, the age of the candle itself, the specific content of the "stearin", the effect of the untrimmed candle wick ...

The SI standard unit for Light is the "Candela", defined as the "Energy emitted from the surface of 1/600,000 meter of freezing platinum" (or so it was, the last time I worked with it).

Interesting also, are the causes of variablity of "sunny 16" sunlight: Particular content (smog), moisture content in the air, deviation from - somewhere, 42 degrees north latitude was specified, time of day, time of year, temperature, possible bird flights between the sun and the meter ...

This is NOT to say that all exposure meter calibration MUST be of "the first order", but "variability"- STABILITY of the standard is important and should be a prime consideration.

 

[Kirk Keyes]

The reason why it is rather variable however is not to be found in the sun itself, but in our geography and weather.

The output of the sun itself actually varies a couple percent as it goes through the sun spot cycle, but out atmosphere does have a bigger potential for varitation.

 

[Q.G.]

We have seen the graph of the sun's variance. It's not impressive.

Weather and geography is what make the sun different, sometimes every few seconds.

 

[Ira Rush]

Wow... I didn't think this topic was so popular!

Wow... since posting this a little less than a week ago, as of now 103 responses and 1,461 viewer hits.... did not think it was such an important or even interesting topic!

Anyway, thank you all who posted, very and I truly mean very interesting insight and information... thanks really.

In case anyone really cares to know... I went old school low tech. Got the "Blad" out, slapped on a A24, loaded with 100VS, and first tested my trusty Gossen Luna Pro-F, both in reflected and incident modes. Shot at suggested exposure then in 1/2 stops, to +/- 3 stops.

Switched meters, this time trying my Minolta-AutoMeter IIIF, switched backs, loaded with a fresh roll, (same emulsion number batch... don't want any color variance to bias the results) same camera body, lens etc. and same procedure as above. All done within a few minutes, so lighting was not that changeable.

The results.... well eyeballing the frames with a loupe and a lightbox, and from reading my notes... in Incident mode both meters were within a 1/2 stop of each other, in reflected mode more like a full stop ( which I think was due to the fact that the Gossen has a 30 degree reflected angle, while the Minolta has a 40 degree angle.

Not very high tech but served my needs.

Thanks one and all,... now for some really heavy reading with all this information.

 

[RJS]

Dr. Henry does mention that the Zone VI modified meter does have an IR filter in the pack installed by Zone VI. I don't find any further mention. However when I think about placing the #87 filter I have for IR film I wonder what will get through and how I could separate the IR from the very dense red filter. Or am I missing the point here. I don't know what filters are in enlargers used for color printing as I printed color only once or twice in the dim, distant past using then-new Cibachrome. Perhaps if I look in the box of filters I purchased at that time for color printing I'll find something. I'll also have to do a lot more reading. Cutting off IR would not, I think require cutting off most visible light. How would a light meter 'see' through such density?

 

[Q.G.]

RJS,

The 87 filter will let IR (and not much else) pass. The filter in the meter will block IR.

Find a broken slide projector, open the lamp housing, and take out the flat piece of glass sitting between the bulb and the slide.
It is an IR filter, blocking IR. Used to keep the heat of the lamp off the slide.

A similar filter is used in colour enlarger. Again so you do not fry the negative.

They are used in meters to correct for the IR sensitivity of the cell. We do not want that to influence the reading we need for non-IR-sensitive films.

 

[RJS]

Ah, once again I had my head turned off. I think I need a vacation from thinking for a few days. Too many piils to cure all the stuff I have. Head like a balloon. More in a few days.

 

[RJS]

Ira, I think you night try a slow speed color transparency film and photograph your grey card pretty much filling the frame. I would use artificial daylight-equivalent lamps in two reflectors, equidistant at about 45degrees to the card to eliminate glare and so you have relatively constant light. I think if you expose as your meter recommends, and vary +and minus 1/3 stop over maybe 2 stops you should get a pretty fair read on how your meter compares with your eloctronically timed either digital or film camera. If the transparency comes really close to matching the grey card I would think you would be good. Once I detox my head I will maybe have a better idea. Or not,

 

[RJS]

Reading a bit more. . . Ctein (pg 34 of his book "Post Exposure") mentions (I paraphrase) that different B&W films differ in their response to different colors. On page 18 he has a graph demonstrating this with TMAX 400 and Kodak Technical Pan. So, depending on the color of whatever you meter, with a well calibrated meter, it would appear your meter may suggest somewhat different exposures. He also discusses many of the variables, most of which have been mentioned in this thread such as shutter speed, erroneous aperture markings and etc. He also suggests what would seem a quite useful method for determining whether your meter is calibrated for a 12% or 18% grey card. Not a big difference, but apparently ANSI specifies 12% and the cards most people have are 18%' A Macbeth color checker card, as Ctein describes using it would also seem to add some useful information.

It's amazing, all things considered, that we get exposures as good as we do. The end of all this mess would seem to be to test your meter with your camera (shutters) and standardize your developing so you get negatives you like to print. The only parameter I can see that needs to be 'accurate' is linearity of meter response.

 

[Q.G.]

Yep. That's that thing many photographers do, called "getting to know your film".
In spite of its name, it is an all including exercise, getting you acquainted with your meter (and the way you use it) and processing chemicals and style as well.

It's hard from shooting and processing films to determine which one of all the 'input parameters' was responsible for a slight deviation from what you would have liked the result to be.
And there are about as many ways to steer the result back to the desired result as there are input parameters.

It will in the end (it may take longer, or be a quick thingy) produce well exposed and processed films, but not help very much if you want to know how accurate your meter is, measured against a standard. Unless you also have a comparison (a calibrated meter, or standard light source) that can be relied upon to adhere to that standard.