Need advice for Spotmeter calibration

[Chan Tran]

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.

I thought about that but then how much is the tollerance on EV? If you are talking about within 1 EV then it's possible.

 

[Alan Edward Klein]

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.

Efficiency and light output reduce with time as well.

 

[wiltw]

I thought about that but then how much is the tollerance on EV? If you are talking about within 1 EV then it's possible.

Shooting color transparency film, one would never tolerate +-1EV, too wide an error range to be acceptable! +- 1/3EV might be acceptable even for some, since film camera lenses could be adjusted in 1/2EV increments.

 

[Chan Tran]

Shooting color transparency film, one would never tolerate +-1EV, too wide an error range to be acceptable! +- 1/3EV might be acceptable even for some, since film camera lenses could be adjusted in 1/2EV increments.

Well 1/3 EV is about 25% and I think most lumen ratings of 100W would be within the 25% of each other. However, aging can lose more light. I realize that tolerance in photography is quite large. I don't really see in any discipline that a measurement of 25% off is acceptable.

 

[Bill Burk]

I think a Heliostat would come in handy about this point. I want to check against a true daylight standard. Imagine having the heliostat aim at a device on my work bench. That device can adjust the brightness through a moving aperture like the put in old automatic cameras

 

[DREW WILEY]

The problem is that seemingly small errors all potentially add up. A meter a third of a stop off... a shutter speed slightly off ... a gray card half a stop off.... pretty soon you might be way out of bounds for a decent chrome exposure, or even a precise negative.

Light bulbs themselves tend to be misunderstood. The kind people buy at typical retail outlets are all basically outsourced trash, and often deceptively labeled. Traditional blackbody tungsten bulbs are now nearly gone. GE is completely out of the bulb mfg business now, although remnants still turn up for sale. They had two completely separate divisions, one being commercial and scientific lighting, with high quality control and good specifications available, the other the Consumer division, geared to high volume with low quality, and full of unreliable marketing BS. That's the way it is with some other companies too. It applies even to enlarger bulbs.

As far as gray cards go, Wilt, I don't care to repeat the whole story. I did full spectrum plots all the way from IR to UV with a FAR more accurate gear than you mentioned. Discovering the sheer lack of acceptable quality control in most brands of gray cards can be seen with the naked eye; but I wanted to quantitatively pin it down. Many were at least half a stop off. But that was just a adjunct project to my main goal, which was to make my own truly neutral 18% gray paint - a trickier task than one might think (for example, no commercial black pigment is in fact neutral black, or white pigment entirely white). But that's a whole other story.

 

[Alan Edward Klein]

The problem is that seemingly small errors all potentially add up. A meter a third of a stop off... a shutter speed slightly off ... a gray card half a stop off.... pretty soon you might be way out of bounds for a decent chrome exposure, or even a precise negative.

Light bulbs themselves tend to be misunderstood. The kind people buy at typical retail outlets are all basically outsourced trash, and often deceptively labeled. Traditional blackbody tungsten bulbs are now nearly gone. GE is completely out of the bulb mfg business now, although remnants still turn up for sale. They had two completely separate divisions, one being commercial and scientific lighting, with high quality control and good specifications available, the other the Consumer division, geared to high volume with low quality, and full of unreliable marketing BS. That's the way it is with some other companies too. It applies even to enlarger bulbs.

As far as gray cards go, Wilt, I don't care to repeat the whole story. I did full spectrum plots all the way from IR to UV with a FAR more accurate gear than you mentioned. Discovering the sheer lack of acceptable quality control in most brands of gray cards can be seen with the naked eye; but I wanted to quantitatively pin it down. Many were at least half a stop off. But that was just a adjunct project to my main goal, which was to make my own truly neutral 18% gray paint - a trickier task than one might think (for example, no commercial black pigment is in fact neutral black, or white pigment entirely white). But that's a whole other story.

Did anyone ever check the accuracy of apertures?

 

[Chan Tran]

Did anyone ever check the accuracy of apertures?

I did some time ago and found they are quite accurate. If the lens has T stops which is less than the f /stop it's generally because of the optics not the aperture blade opening of the wrong size.