Need advice for Spotmeter calibration

[BrianShaw]

But, to counterpoint that method...if I believed Sunny 16 to be a good rule of thumb, if I 'calibrated' my incident meter to f/16 within the past 2 weeks, it would be -0.2EV compared to pre-'calibration', and if I calibrated my incident meter to f/16 a few months ago, it would currently be -0.7EV compared to the same pre-'calibration' measurement. IOW the calibration brightness had CHANGED by 2/3EV just depending upon when I did that procedure shown in the video?! Yes, it is a WAG, but not close enough to be scientific.

So in addition to "excercising" the Hasselblad shutter every three months, one could re-calibrate their lightmeter to Sunny-16 every week or two.

 

[koraks]

So in addition to "excercising" the Hasselblad shutter every three months, one could re-calibrate their lightmeter to Sunny-16 every week or two.

Don't forget the obligatory CLA every year. And when everything's done, re-establish your "personal zone system EI" for the materials used.

 

[wiltw]

So in addition to "excercising" the Hasselblad shutter every three months, one could re-calibrate their lightmeter to Sunny-16 every week or two.

Was that spelled correctly...did you really mean that you need to exorcise the devil from your Hasselblad shutter from time to time?

 

[Sirius Glass]

Was that spelled correctly...did you really mean that you need to exorcise the devil from your Hasselblad shutter from time to time?

Yes, but one has a devil of a time doing that without a good watch to work ratio.

 

[DREW WILEY]

Which "Sunny 16"? - what latitude, what time of year, what elevation? How many clouds or flying buzzards are permissible in the sky?
Sunspots or no sunspots? Atmospheric pollution or not?

 

[Sirius Glass]

Which "Sunny 16"? - what latitude, what time of year, what elevation? How many clouds or flying buzzards are permissible in the sky?
Sunspots or no sunspots? Atmospheric pollution or not?

Middle latitudes, between 10am and 4pm local time if I remember correctly, so this might not work for people in Scotland or Finland. Remember this is an approximate standard for those that want a quick sanity check before sending all the equipment to a calibration laboratory. As I noted I send my equipment out to calibration laboratories.

 

[RalphLambrecht]

Don't forget the obligatory CLA every year. And when everything's done, re-establish your "personal zone system EI" for the materials used.

Calibrating a light meter is not trivial and often requires special equipment. However, testing a light meter against a known and stable light source, such as the sun, is easily done and useful. I do it once a year unless suspicious results demand a check.

 

[Sirius Glass]

Calibrating a light meter is not trivial and often requires special equipment. However, testing a light meter against a known and stable light source, such as the sun, is easily done and useful. I do it once a year unless suspicious results demand a check.

Sage advise from an experienced photographer and I concur with his recommendation.

 

[DREW WILEY]

Hmmm.... The fog here lifts about two months of the year ... Do I need to recalibrate two stops off? If I drive inland, they've got smog instead. One stop difference? (or four stops difference if you're in Bakersfield).

 

[Alan Edward Klein]

Middle latitudes, between 10am and 4pm local time if I remember correctly, so this might not work for people in Scotland or Finland. Remember this is an approximate standard for those that want a quick sanity check before sending all the equipment to a calibration laboratory. As I noted I send my equipment out to calibration laboratories.

Remember years ago those Kodak instruction inserts in boxes of film? They called for measurements between 10 a.m. and 2 p.m., not 4 P.m.

I just checked their current instructions for Gold 100. They suggest f/16 and 1/125 on sand or snow and f/11 on bright or hazy sun with distinct shadows, based on the sun between two hours after sunrise and two hours before sunset.

 

[BrianShaw]

It’s a rule of thumb, and thumbs come in a wide variety.

 

[DREW WILEY]

Just like the old adage to use the palm of your hand in lieu of a gray card, but one stop higher. ... as if gray cards themselves didn't vary enough!

No sun today! I did, just now, manage to get a break in the wind and rain long enough to rake up the downed branches all over the driveway.

 

[Chan Tran]

Just like the old adage to use the palm of your hand in lieu of a gray card, but one stop higher. ... as if gray cards themselves didn't vary enough!

No sun today! I did, just now, manage to get a break in the wind and rain long enough to rake up the downed branches all over the driveway.

The back of my hand is good for gray card. While it's not neutral in color the B&W refection density is near 0.75 density last time I check.

 

[wiltw]

Just like the old adage to use the palm of your hand in lieu of a gray card, but one stop higher. ... as if gray cards themselves didn't vary enough!

Over many decades of involvement in photography, I have accumulated a variety of products that have '18% grey' areas for metering, I can count 6 different products that I still possess even today..., and just now metering all of these I find only one of them varied from the others by 0.1EV even though the vintage of origin varies across a span of half dozen decades.

Using the Lightroom eyedropper tool on the above shot, the 6 areas generally fall into the range of about 37 - 43, with several of them reading 40-41. Due probably to the usage only for density, and not as widely for NEUTRALITY (neutral grey) it is visible that one of these cards (center) is visibly warmer than others; while it was sold to me as a 'vintage' Kodak-sourced card, it did not come with any packaging to vouch for its authenticity from Kodak. (The four Kodak cards are grouped together, left to right, 3 having original Kodak packaging.), #5 is Douglas, #6 is MacBeth Colorchecker, #7 is EZ Balance and cropped out of the shot above the other 6 samples.

As for the palm of my hand, over the years I have read values that have varied from +1.0EV to +1.5EV compared to grey card, but generally over the past couple of years +1.2 to +1.3EV is the range.

As already stated, the 'thumb' can be pretty wide and there are different thumbs, but the 'thumb' gets you in the ballpark, it serves as a 'sanity check', but is hardly a calibration standard.

 

[DREW WILEY]

Wilt - Even the pic you've posted shows how wacky the quality control is. I've already recited in numerous threads how I once took entire stacks of gray cards of various brands and measured them on a full-spectrum industrial densitometer. Not only were none of them actual neutral gray, but none were sufficiently close to 18% reflectance - sometimes as much as 15% off. Then there's problems of differing sheens and potential fading or discoloring over time.
That kind of unreliability is utterly unacceptable for any kind of accurate work, especially if chrome film is involved.

Same in principle goes with current collapsible gray discs, now popular with digital shooters. I have exactly one of them which is spot on, and way better than the average gray card. Just like checking light meters or darkroom thermometers, everyone potentially needs a reliable reference standard. I use the grayscale on the MacBeth Color Checker Chart. I've even cross-checked that many times with densitometry. The patches are precisely spaced between white and black, with a true 18% gray in the middle. Of course, these need to be kept clean and protected from fading. Even with all the problems of accurately representing hues over the web, the only example you show in the pic that actually looks gray is the MacBeth version.

The definition of a ballpark can be pretty big. When playing little league out in the country as the only white kid on the Indian Res team, I was always told to go to left field, meaning in my case, clear over the barbed wire fence and into the next pasture.
(I was bad at baseball).

 

[Bill Burk]

A good test reference is a backlit panel having a bright tungsten light source (e.g., quartz halogen kitchen range light fixture on its back with one bulb pulled out) and color corrected with a blue (e.g., 80B) filter. Arrange the panel to light distance so that it has 100 Foot Lamberts luminance according to the reference meter (e.g., Sekonic). Correct me if I am mistaken but I think the reading would be ASA100 f/10 1/100 second.

Sure, calibrate the Minolta to agree. It’s just a dial you can turn back to zero if it doesn’t work out.

 

[DREW WILEY]

Wilt - Even the pic you posted shows how wacky the quality control is for most "gray" cards. And meters are designed with a certain peak spectral sensitivity in mind.

I've already recited in numerous threads how I once took entire stacks of gray cards of various brands and measured them on a full-spectrum industrial densitometer. Not only were none of them actual neutral gray, but none were sufficiently close to 18% reflectance - sometimes as much as 15% off. Then there's problems of differing sheens and potential fading or discoloring over time.
That kind of unreliability is utterly unacceptable for any kind of accurate work, especially if chrome film is involved.

Same in principle goes with current collapsible gray discs, now popular with digital shooters. I have exactly one of them which is spot on, and way better than the average gray card. Just like checking light meters or darkroom thermometers, everyone potentially needs a reliable reference standard. I use the grayscale on the MacBeth Color Checker Chart. I've even cross-checked that many times with densitometry. The patches are precisely spaced between white and black, with a true 18% gray in the middle. Of course, these need to be kept clean and protected from fading.

Even with all the issues of hue representation over the web, the only example in Wilt's pic which does look neutral gray is in fact the MacBeth version.

The definition of a ballpark can be pretty big. When playing little league out in the country as the only white kid on the Indian Res team, I was always told to go to left field, meaning in my case, clear over the barbed wire fence and into the next pasture.
(I was bad at baseball).

 

[Chuck1]

I can't remember where but I think i once saw something about a 100(?) watt bulb having a standard EV at a specific distance, don't know if that sounds familiar to anyone( it may be from Adam's the camera )

 

[DREW WILEY]

A myth. It would have to be wired into a sophisticated feedback circuit with its own internal monitored light metering system and regulated power supply. The better enlarger colorheads operate on that principle. But all it takes is a smudge or cobweb somewhere in the light path to spoil to equation.

Old school spectrophometer bulbs had to be broken in before official use, and then were monitored for a restricted lifespan before being replaced on schedule. Now an entirely different kind of light source is used.

 

[MattKing]

As an aside, the reason that Eastman Kodak only provides limited time range reciprocity failure information for their films is that there are no manufacturers who make spectrophotometer equipment that provide sufficiently reliable and repeatable and consistent low light level sources in order to objectively test the extremely low amounts of light that correspond to exposure times of several minutes.
There are lots of people who provide subjective tests in those exposure time ranges, but no purely objective ones.

 

[Chan Tran]

I can't remember where but I think i once saw something about a 100(?) watt bulb having a standard EV at a specific distance, don't know if that sounds familiar to anyone( it may be from Adam's the camera )

100W bulbs have different Lumen ratings (and then are the ratings correct and also the ratings are for all directions) so they don't give out same amount of light. Some give out more light and some give out less light than others.

 

[DREW WILEY]

We're right back to needing already calibrated lux meters, Chan. The advertised lumen rating of a bulb is only nominal, and the actual output is going to vary anyway unless the voltage is tightly controlled. There are additional variables too.

Astronomers rely on a special kind of white dwarf star, and then factor the Doppler shift. The fixtures in my lab ceiling aren't distant enough for that to work for me.

 

[wiltw]

Wilt - Even the pic you've posted shows how wacky the quality control is. I've already recited in numerous threads how I once took entire stacks of gray cards of various brands and measured them on a full-spectrum industrial densitometer. Not only were none of them actual neutral gray, but none were sufficiently close to 18% reflectance - sometimes as much as 15% off. Then there's problems of differing sheens and potential fading or discoloring over time.
That kind of unreliability is utterly unacceptable for any kind of accurate work, especially if chrome film is involved.

Same in principle goes with current collapsible gray discs, now popular with digital shooters. I have exactly one of them which is spot on, and way better than the average gray card. Just like checking light meters or darkroom thermometers, everyone potentially needs a reliable reference standard. I use the grayscale on the MacBeth Color Checker Chart. I've even cross-checked that many times with densitometry. The patches are precisely spaced between white and black, with a true 18% gray in the middle. Of course, these need to be kept clean and protected from fading. Even with all the problems of accurately representing hues over the web, the only example you show in the pic that actually looks gray is the MacBeth version.

The definition of a ballpark can be pretty big. When playing little league out in the country as the only white kid on the Indian Res team, I was always told to go to left field, meaning in my case, clear over the barbed wire fence and into the next pasture.
(I was bad at baseball).

But all of them except one metered to identical results, and any difference was only measurable by the Lightroom eyedropper too, and only one of the cards was not absolutely neutral (difference of more than 0.1 in any color using the eyedropper to show values of R-G-B. So where is the 'beef', so to speak?

 

[RalphLambrecht]

100W bulbs have different Lumen ratings (and then are the ratings correct and also the ratings are for all directions) so they don't give out same amount of light. Some give out more light and some give out less light than others.

Plus, in the EU, they are no longer available.

 

[wiltw]

I can't remember where but I think i once saw something about a 100(?) watt bulb having a standard EV at a specific distance, don't know if that sounds familiar to anyone( it may be from Adam's the camera )

That is unlikely. I know that different model 60W bulbs made by GE had different lumen output ratings listed on the packaging. So I doubt that 100W bulbs from different manufacturers (or even different models of bulbs by same manufacturer) have any consistency of output.