Alternative Light Meters

[Randy Stankey]

I remember the Swinger camera. I had one when I was in high school. I thought it was cool because it was easy to make double exposures with. I remember the exposure meter but mine only said "YES." It didn't have "NO."

The camera had a looped wrist strap with a plastic T-handle and that was what you used to hold the camera while you gripped the pull tab to take out the picture. If you didn't use the T-handle and tried to hold onto the camera body, there was a good chance that you would rip off the pull tab, leaving the picture hanging partially out of the camera.

Maybe that's why they called it "Swinger" because you literally had to let the camera swing on its handle in order to use it.

I can't say, for sure, that my idea of using the extinction principle will work but I really do think it is something that could be used to develop a workable solution to the problem of estimating screen brightness and translating the results into a simple yet meaningful answer.

Let's say that we had a small telescope about six inches long with a dial similar to a focus ring with graduations on it. It would be similar in design to a handheld refractometer. The user looks through the scope, turns the ring until he gets the correct picture then reads the result from a graduated scale. Pair that with a custom test pattern in the projector that has a checkerboard pattern on it like the one inside the Swinger camera. Maybe it could even have the words "YES" and "NO." (Or some other meaningful words.) The test pattern could even have instructions printed right on it.

To use it, put up the test pattern and set the theater lights to the regular settings that you use to show your feature. Go into the back row of the theater then give yourself a couple of minutes for your eyes to adjust. Point the scope at the screen, turn the dial until the correct image is seen then read the result.

The scope could be set up with the zone system, numbers 1 to 10, like photographers use or it could be some arbitrary scale of brightness values. It doesn't really matter as long as the scale is consistent.

Let's say that you're supposed to get a brightness value of 6, plus or minus 1. If you don't get 6 ±1 then you have to adjust your projector accordingly. If you can't get the projector to make the right light, it's time to call your technician.

Since the tech has already calibrated the brightness with a proper meter and has taken a reading with the extinction scope, he should already have a good idea of what's going on in the theater before he gets there.

I understand what Harold says. Yes, there could be a few problems with the idea that could turn into "gotchas." I've had this idea rattling inside my head for a while and I really believe it could work if only I had time to experiment with it and see how well it works.

Unfortunately, I don't have time, money and resources to do the proper experimentation.

If somebody else wants to pick up this idea and run with it, that's okay with me. I'm not in this world to get rich. Just give credit where credit is due and that's enough for me.

[Kenneth Wuepper]

I recall that Ansel Adams, the photographer, had an exposure meter that operated in a very peculiar way.

There was a scope and it had the filament of a lamp in the center of the viewed image.

You turned the brightness of the lamp until it disappeared into the image. The brightness control was calibrated so you knew how much light you were measuring.
This was really very accurate once the operator gathered the skill to use it.

This was a very early form of "spot meter". I never owned one but did get to look through one and turn the brightness control while observing the result. There was a learning curve to it.

[Mark Gulbrandsen]

Well, Adams also used the Zone System. Early exposure meters ARE very strange. Really early ones had the typical 90 volt battery plus two other smaller batteries. They were large and heavy. Used a phototube as the sensor. Here is an interesting article on adapting the Zone system to digital photography....

https://fstoppers.com/education/how-...l-world-417047

[Mitchell Dvoskin]

The Panavision Screen Brightness Meter pictured below worked by looking through the viewfinder while pointed at the screen. In the viewfinder there was a brown ring superimposed over the image. You would turn the black knob until the center of the ring filled in with identical color/contrast/brightness turning it into a big round ball over the image. Then the meter on the side would indicate how many foot lamberts are reflecting off the screen.

brightness meter.jpg

[Randy Stankey]

I have a Gossen Luna Pro meter that I use with my Rolleiflex Automat.

It still works great. I check it, occasionally with a gray card. (Shoot a gray card at the meter's recommended setting then develop the film and compare to a gray card.) The meter always produces good results.

The only problem with it is that it uses a mercury battery which isn't made anymore. I was told that there is an adapter that allows you to use a regular button cell battery but they say that it isn't as stable and doesn't last as long as a Mercury battery. I've had it for years and the battery is still good, though.

A while back, I was out shooting around with my Rollei when I spotted the Flagship Niagara (Tall Ship from the War of 1812) headed for the channel to Presque Isle Bay. (The entrance to Erie's harbor.) I high tail it out to the pier and get there just as she's entering the channel.

It was a bright, sunny day and I had the camera loaded with Tri-X 400. Not a lot of headroom, there, but I figured that the film would have enough latitude.

There was another guy there with a big digital Nikon on a tripod and he had a big zoom lens on. Practically more lens than camera!
I figured with an expensive rig like that, the guy would know something about photography. I asked the guy, "Hey, I'm shooting 400 speed. Do you think I ought to overshoot by one stop or two? I can pull it back when I develop."

He was "machine gunning" the camera. He barely looked away from the viewfinder and said, "I dunno'... I'm spot metering."

I held up the Gossen, clicked off a high reading and a low reading then figured the average in my head. I said, "Well, if I wanted to spot meter, I'd have to get my feet wet." Then I stepped back a couple of strides from the edge of the pier and bracketed off two shots.

I left the pier and he was still clicking off shots like an M-16.

That picture hangs on the wall of my living room and I sold three other copies for $200 apiece but I have no idea whether that guy got even one good shot out of the fifty or sixty he snapped off while I was there. I exhibited in just about every show in town, that year.

If he did make something of it, I feel certain that somebody would have said, "Hey! Did you see that other photo of the Flagship that looks just like yours?"

[Kenneth Wuepper]

Digital photography has made users sloppy. Since "they don't cost anything" there are a lot of captures. Seems that if you take enough. one has got to be good (or at least acceptable!)
New terms have emerged like exposures are now called captures.

[Jay Glaus]

I had a Spectra Cine Spot which I sent in for repairs at the beginning of Covid. Seems through all the lock downs it managed to get lost there and no one could ever find it. Still mourning to this day.

If anyone on here by chance knows anyone with any pull at Spectra, please kindly pass a long a message from me... “HELP ”

[Marcel Birgelen]

Harold - there is no dark period for DLP or (Sony) SXRD projectors. It's a constant luminous flux, only modulated by the individual imager pixels.

I've always asked myself how the light modulation of DLP works exactly. Yeah, we know that it modulates light by rapidly flashing a mirror "on and off" per "sub-pixel" (per color per pixel). Unfortunately, there isn't much information available about how this modulation works exactly, only that the pulse-with modulation is done entirely digitally, so it probably runs on a master clock with a certain frequency.

So, what I'm wondering is: If I display a uniform grey screen (every pixel contains the same color), will all individual pixels be modulated equally or will there be differences in e.g. phases of the different pixels or even between sub-pixels?

I don't think this matters much for most light meters, as the DLP modulation frequency will probably exceed any interference threshold in the meter, but it's something I found to be intriguing and something that's only sparsely documented.

[Randy Stankey]

I imagine that a light meter that uses the human eye as a detector should probably do all the integration or averaging that is necessary. Shouldn't it?

If a projector produces an image intended to be viewed with the human eye then it stands to reason that the eye should be the best judge. Right?

This is assuming that the person making such measurements is doing so under standardized conditions and has no health problems or vision impairments.

Making brightness measurements in a darkened movie theater with prescribed light levels, using equipment and procedures designed to certain specifications should be "standard" enough.

Also remember that my idea is not intended to be an absolutely precise "final answer" but just good enough for daily use. It's meant to be simple, cheap and to make it easier to communicate with a knowledgeable technician in a way that a person of average training and intelligence can understand.

[Carsten Kurz]

I've always asked myself how the light modulation of DLP works exactly.

TI has published some papers over the years, but I think the actual behaviour of current cinema DLPs is not documented. Especially when it comes to features like 3D flashing, the different frame rates, etc.
However, I guess it should be easy enough to zoom up a large picture and place a photodiode in the center of a pixel, connected to a storage oscilloscope. Using suitable RGB patterns should give some insight. A second diode/channel on a different pixel could tell us something about 'interpixel timing'.

[Gordon McLeod]

I remember back in the early days of D cinema John Pytlack said the for DLP a photovolopitc response was still needed as was for film

[Mark Gulbrandsen]

I remember back in the early days of D cinema John Pytlack said the for DLP a photovolopitc response was still needed as was for film

I think he was thinking spectral response.

[Gordon McLeod]

I think he was thinking spectral response.

No he was very clear about it as was Glen Bergren

[Mark Gulbrandsen]

No he was very clear about it as was Glen Bergren

Well, there has never been flicker in any DLP because of the limited range of the moving mirrors. Only in 3-Dee. So it couldn't be that.

[Carsten Kurz]

I just received a quote from TLS in the UK - the TLS digital screen checker (the same device sold by Harkness) dropped in price considerably, as it seems. It is now around 350US$ + VAT + shipping.

https://www.tls.uk.com/TLSUKLtd.html?ID=ScreenChecker

As far as I know, the integration time is also suitable for film projectors.