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#1 Ira Ratner

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Posted 09 November 2008 - 08:25 AM

Bought myself another toy off eBay, and the thing is built like I tank. But I'm confused.

With this old analog meter, you hit the trigger and a motor moves the dial/exposure indicator. There's a handy dandy, easy to read cine scale with an fps range of 8 to 128, and there's a large reference line/mark for 24fps, naturally because this is the frame rate most people will shoot at.

However, this mark is not lined up to a shutter speed of 60. It's about two thirds of the way from 30 to 60, which would make it around 50. I could understand if it was dead center making it 45, but 50?

The rub is, my K3 indicates a shutter speed of 1/60 for 24fps.

To anyone's knowledge, was there a "standard" shutter speed for home cine cameras way back when that this is referencing? (The meter was made in 1968.) I would think it would be easier for me to just change the ASA dial if I have to make an adjustment to get this thing working accurately, but shooting 100 reversal, my only other choices are 80 and 125.

Finally, before tearing up any film, I planned to cross-check it with a digital camera set on manual, but is that a stupid plan? Like, can I expect an acceptable correlation between how a digital sensor works and how actual film is exposed?
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#2 Adrian Sierkowski

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Posted 09 November 2008 - 09:15 AM

24 FPS in film cameras is 1/48th of a second. If you know your K3 to be 1/60th of a second use that. I would think they would reference 180 degree shutter as that's pretty commonly the "standard." there is some deviation to it; of course, but it seems through all my reading to be the once reference.

Another way of doing it is:

shutter opening in degrees/(360*frames per second)

or if you have a 180 shutter as I do, then 1/(2xfps)
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#3 Ira Ratner

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Posted 09 November 2008 - 09:28 AM

The K3 is definitely 1/60 at 24fps, so does that mean I would use that reading for 1/48 and open 1/3rd of a stop?
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#4 Adrian Sierkowski

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Posted 09 November 2008 - 09:30 AM

I'd double check with the meter; but I'm betting the 1/60th reading and the 1/48th reading+1/3 would be the same. Normally you'd want to use the 1/60th of a sec exposure as it should be the proper exposure time regardless of frame-rate.
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#5 Ira Ratner

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Posted 09 November 2008 - 09:40 AM

Thanks for the help, Adrian.

But do ASA sensitivities correlate like F steps? In other words, if I do a test in a controlled situation using the 80 ASA setting for shooting with 100, is that representing my 1/3 stop over?

The main thing is, I'm trying to figure out a way to use that large 1/48 mark as my reference, as opposed to trying to read the tiny ones and do math.
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#6 K Borowski

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Posted 09 November 2008 - 01:47 PM

I'd double check with the meter; but I'm betting the 1/60th reading and the 1/48th reading+1/3 would be the same. Normally you'd want to use the 1/60th of a sec exposure as it should be the proper exposure time regardless of frame-rate.


Gee Adrian, who told you that? :P


Yes, shutter speeds are, theoretically, the same as a full stop, say from 1/60 sec. to 1/30 sec.

But you have to keep in mind that shutters, stops, ISO speeds, even light meters all have tolerance.

Even the speeds and numbers themselves are rounded. This is why 1/48 and 1/45 are the same thing, because technically, half of 1/8 is 1/16. Half of that is 1/32, and between 1/64 and 1/32 is 1/48.

Yet this speed is referred to as 1/45.

To get around the fact that the shutter may be old and slow, lens might loose more light than the stated F/stop (unless you're lucky enough to have exact T-stops), and film companies are famous for over-rating film, you want to OVEREXPOSE with color or B&W negative film.

Rate the film 1/3-2/3 stop less than its box speed as a rule, and test first, just in case your equipment is out of alignment.

Most labs are happy to process a test strip of film when you are testing a new camera.

Just call them up and ask.


As for using a digital camera as a benchmark, no that is a great plan, and eliminates a lot of the variables and complexities of testing.
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#7 K Borowski

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Posted 09 November 2008 - 01:54 PM

But do ASA sensitivities correlate like F steps? In other words, if I do a test in a controlled situation using the 80 ASA setting for shooting with 100, is that representing my 1/3 stop over?

The main thing is, I'm trying to figure out a way to use that large 1/48 mark as my reference, as opposed to trying to read the tiny ones and do math.


Yes, every 1/3 stop of exposure is, rounded, a change in density of log .1 if you're reading the film with a densitometer. Even here, the numbers are rounded, but yes 80 is 1/3 stop more than 100, so you could set that by changing F/stop to open up by 1/3 or change shutter angle by 1/3 if you weren't using a K3.

If you want to use 1/48 (45) sec. as reference, just treat it as half a stop faster than 1/30, half a stop slower than 1/60.

You couldn't correlate that to ASA, as it's in 1/3s, or shutter angle with the K3, but simply opening a half stop to take into account the fact that your exposure let's in 1/2 stop less light from the 1/48 "cine" meter reading will give you a more-or-less exact conversion.

So, you kinda are still doing math (don't trick yourself and close down 1/2 instead of opening up 1/2 stop!), but it should be enough for a math-stupid cinematographer to handle ;)

Lol. Then again, you seem to be so good at math you managed to come up with a way to process E6 in 3 steps instead of 7. So things like integration, derivation, and logarithmic formulae should be fun for you, right? :P
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#8 K Borowski

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Posted 09 November 2008 - 01:56 PM

Sorry, I always do this: EI 80 is 1/3 stop *slower* than EI 100. To protect film you rate it slower than box speed.
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