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Old July 30th, 2005, 11:01 AM   #1
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Light Meter w/ 35mm Adapter

Would someone with the know-how like to post instructions on how to properly use a light meter when using a 35mm adapter?

There are settings on a camcorder to control light (e.g. shutter, exposure, ND filters) and we also have the F-stop settings of the 35mm lens. How to properly use them together would be valuable info.

Some of it may be subjective based on what "look" your going for. But hopefully there are some basic procedures that will help.
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Old July 30th, 2005, 12:14 PM   #2
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Great idea! I guess there would be subtle difference when running through the 35mm lens and into the mini DV cam. Good thought, Donnie!
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Old July 30th, 2005, 12:30 PM   #3
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If you aren't using a light meter with your unadorned camera, you won't need one with a 35mm adaptor either. Set the f-stop of the 35mm lens based on the degree of shallow depth of field desired; many people keep the lens wide open, but there may be instances with longer lens that the background is too soft or the focus too shallow to be practical, in which case you may want to stop down a little. At some point however, the groundglass will become visible, so you need to determine what your usable range of f-stops are.

Once the 35mm lens is set, you can then proceed to set exposure on the camcorder. As light levels fluctuate, use your camcorders aperture, shutter and ND settings to maintain desired exposure. If you do elect to adjust the depth of field, maintaining consistent exposure is easy as there is a 1:1 compensation ratio between the lenses; i.e., stopping down 1 stop on the 35mm lens will require you to open up 1 stop on the camcorder's lens (or halving the shutter speed).
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Old July 30th, 2005, 12:55 PM   #4
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Are you certain of that? That is what I always figured, but I felt that I noticed in practice that 1 stop on the camera wasnt necessarily equal to one stop on the 35mm lens. For example I mainly used an f1.4 lens and f2.8 35mm lenses and they didnt seem to end up being 2 stops different when viewed through the camera. I recall someone else posting a similar observation but I do not remember who or where. I could be way off, but is it possible this is the case, perhaps due to the complexities of diffusing light through a ground glass? I guess all it would take is a test, but I do not have my old 35mm adapter or camera immediately available to me at the moment.
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Old July 30th, 2005, 01:12 PM   #5
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That's an interesting point, Noah, but my guess is that it might have more to do with the calibration of the 35mm lens than anything else. In other words, from f2 to f2.8 you should see a halving of the light transmission, but in practice the lens may be delivering more or less. This is why cine lenses are calibrated with T stops that are based on actual transmission rather than theoretical. It's also possible that the camcorder has the same non-linear issue with its lens, which could enhance the problem further. This further proves the folly of using a light meter in this situation. A waveform monitor will be a much more accurate indicator of proper exposure.

I can't see why a ground glass could affect relative levels of light hitting it, but if someone else has a theory on this, I'm all ears.

My experience from using standard speed (T2.1) vs superspeed (T1.4) lenses at fully open apertures is that I have to use twice as much light with the standard speeds as I would have expected.
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