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Still Light Meter for Super 8 exposure


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#1 jaysonwilko

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Posted 16 May 2012 - 03:17 PM

Hi. I've got a Eumig Makro Sound 66XL with a shutter angle of 225 degrees. I use a Polaris light meter to find exposure (I am saving money for a proper light meter but this was cheap and accessible to me at the time.) The light meter is designed for stills (uses shutter speed rather than shutter angle) but I want to make sure I am doing my calculations correct. I set my ISO to my film stock. and then the tricky part. A 225 degree shutter angle works out to 1/40 (rounded up from 38.4). My light meter doesn't show a reading for 1/40 so I take a reading at 1/30 and another at 1/50. The difference is usually about 1/3 to 2/3 of a stop. I set my exposure based on this number and try to favor slightly underexposing to overexposing. Does this sound like a good/accurate process for determining exposure based on my limited equipment? Any input or tips from more experienced film makers is welcome. I am here to learn.
Thanks,
Jayson L. Wilkins
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#2 Richard Tuohy

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Posted 16 May 2012 - 07:14 PM

Hi Jayson,
With a super 8 camera, taking the shutter angle into account is only part of the story. you also need to factor something for the light lost due not having a mirrored shutter. Some of the light coming into the lens is being divided off and sent to the viewfinder, and only part of the light entering the lens is getting to the film. How much exactly? Well, good quesiton. The only way to find out is to do a carefully bracketed exposure test using reversal film.
Here is a page on my lab website that explains how I recommend shooting an exposure test for using an external light meter:
http://nanolab.com.au/bracketed.htm
cheers,
richard
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#3 jaysonwilko

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Posted 16 May 2012 - 07:46 PM

Thank you. some excellent information in there that I hadn't thought to consider. Thanks for the response. But back to the original question, as long as I compensate for the light loss in the viewfinder does the process listed above sound like a good one? some of the stuff Ive shot in the past looks good but some of the shadows are a little crushed on Ektachrome 100D but I shot that stuff when I first got the camera and have refined the process a little since then. Ive got some Vision 2 500T that I need to get processed and I can't wait to see the results from that.
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#4 Richard Tuohy

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Posted 18 May 2012 - 07:35 PM

Thank you. some excellent information in there that I hadn't thought to consider. Thanks for the response. But back to the original question, as long as I compensate for the light loss in the viewfinder does the process listed above sound like a good one? some of the stuff Ive shot in the past looks good but some of the shadows are a little crushed on Ektachrome 100D but I shot that stuff when I first got the camera and have refined the process a little since then. Ive got some Vision 2 500T that I need to get processed and I can't wait to see the results from that.


Hi Jayson,
well, the proceedure you specified was - set the meter to the asa of the film, then take readings at 1/30th and 1/50th and split the difference. That would work if there was no viewfinder loss. Factoring in for the viewfinder loss would mean that this should work. But how can you factor for the viewfinder loss? Well, if you were wanting to get this right, you would have to shoot a bracketed test as I describe on that web page then look at the results.
I think it is easier to adjust the asa setting than the shutter setting on the meter. By making the adjustment with the asa setting, you can simply double the fps rate to get the correct shutter setting.
Here's what I mean. Lets say you shoot your bracketed test (which is essential by the way if you plan on shooting on reversal film like ektachrome or tri=x, but not so essential when shooting on neg, and the test itself MUST be done on reversal film, not neg). Lets say you want to shoot at 24fps. So you set the shutter speed on the light meter to 1/50th, allowing the compensation for BOTH the shutter angle of the camera and the light loss by the viewfinder to be done via the asa setting. You then shoot the bracketed test, adjusting the asa with each shot. Then, when you get the film back, you can decide which is best. Lets say the best shots were had when you had set the asa 1 stop slower than the nominal rated speed. Fine - that's all the correction you will need. If it was Ektachrome, then that means you decided the best results were had when you set the asa to 50. Now, all you have to do in future for any film stock is compensate by this 1 stop setting. And all you have to do for any fps rate you want to shoot at is make like there was a 180 degree shutter and double the fps rate. This way, the one test has allowed you to determine the correct settings for any asa film and any fps rate. You don't have to do any 'split the difference' and you don't have to to work out shutter speeds for other frame rates other than simply doubling them.
Of course, this is only one way to do it. It doesn't really matter how you take the two factors of shutter opening angle and viewfinder light loss into account, as long as you do. I just think that by making the correction with the asa rather than the shutter speed setting, you make life easier.
Do remember, that this test MUST be done with reversal film. Shooting on negative won't inform you about the accuracy of your exposures.
You did mention initially something about 'tending towards underexposing rather than over exposing'. Well with reversal film, you don't want to do either. Underexposing will block up your shadows, increase your contrast (a lot) and increase colour saturation. Overexposing will blow out your highlights, reduce contrast, and reduce colour saturation. 'Incorrect' exposure in either direction will result in lost information. It just wont be there. For 'optimal' results, you want 'correct' exposure (he says in 'scare quotes' because there really is no such thing as 'correct' just results that are 'desired' - and with reversal, desired results have to be achieved 'in camera').

Edited by Richard Tuohy, 18 May 2012 - 07:38 PM.

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#5 jaysonwilko

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Posted 19 May 2012 - 10:00 PM

Thanks Richard, I will be conducting more tests as soon as I order more Ektachrome stock, thanks for the input.
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