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Light Meter Settings K3 150 Deg shutter?


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#1 Taylor Magyar

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Posted 15 January 2009 - 05:05 PM

I have just purchased a Sekonic L 358. In cine mode it is pre set for a 180deg shutter. The manual says to subtract a 1/3 stop from your iso for 160deg shutter. so iso 100 would be rated at 80 for a 160deg shutter. Since the K3 is 150deg where does that put us/me? What have you all done on your meters?? Any help would be great!
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#2 Jason Debus

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Posted 15 January 2009 - 07:56 PM

These are the K3 shutter speeds (from the K3 manual):

fps shutter
8 = 1/20
12 = 1/30
16 = 1/40
24 = 1/60
32 = 1/80
48 = 1/120
frame = 1/30
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#3 Jim Hyslop

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Posted 15 January 2009 - 11:13 PM

You could write out Jason's table, or you could memorize this formula, which will hold true for all cameras and all light meters:
shutter angle
shutter speed  =  -----------------
					  360 x fps

If you plug 24fps and a shutter angle of 150 degrees into the formula, your calculator will tell you 0.0173611111111. Hit the "1/x" button and you get 57.6 - the shutter speed is 1/57.6 second, or approx. 1/60.

Or, to go straight to the "60" just flip the formula over:
360 x fps
-----------------
  shutter angle

360 * 24 / 150 = 57.6, which rounds to 60.

--
Jim
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#4 Taylor Magyar

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Posted 15 January 2009 - 11:44 PM

Thank you both for your help however I am still a bit confused. Please bear with me as I am coming over from a digital environment and am attempting to teach myself the basics of film. I should have mentioned that I understand the shutter speed at 24fps is 1/60 and the shuttle angle is set at 150 deg. The light meter however bases its calculations on a 180 deg shutter angle. What I am trying to figure out is the fraction of a stop that I need to subtract from the film's ISO to make the meter accurate with a 150 deg shutter? As the manual states its -1/3 stop down to 160 deg shutter angle. So I guess we are talking a little more than 1/3 to compensate down to 150 deg?? Or should I be plugging something different into the light meter??
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#5 Taylor Magyar

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Posted 16 January 2009 - 12:06 AM

I think I might be understanding that I should skip entering 24fps and opt for 1/60 shutter speed instead? FPS and shutter speed are the same menu item on a 358- so by doing this no compensation is needed- correct? I'm using shutter speed rather than fps because i know the shutter speed at the given fps for the K3! Am I on the right track?
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#6 Ian Cooper

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Posted 16 January 2009 - 03:24 AM

I think I might be understanding that I should skip entering 24fps and opt for 1/60 shutter speed instead? FPS and shutter speed are the same menu item on a 358- so by doing this no compensation is needed- correct? I'm using shutter speed rather than fps because i know the shutter speed at the given fps for the K3! Am I on the right track?



The L358 allows you to add exposure compensation to the metered reading in 0.1 stop increments, so if you wanted it would be possible to calculate the difference between 1/48th second (180 degrees) and 1/57.6th second (150 degrees). I can't be bothered exercising the brain cells at this time of the morning to do the calculation on paper, but this online tool gives the difference to be 0.263 stops. This means you could adjust the meter by 0.3 of a stop, or you could alter the film's ASA rating by 1/3 of a stop. The difference between 0.3 and 0.3333 isn't worth worrying about.

Out of interest, the exposure time with a 160 degree shutter is actually 1/54th second... and the difference between that and 1/48th second is 0.17 of a stop, ...that can be rounded up to 0.2 which is almost a third. In practice a difference in exposure of 1/3 stop isn't worth worrying about. But it goes to show that the instructions in the manual aren't mathematically precise.


In practice with your meter you can either use the 'non-cine' section and set the meter to 1/60th second shutter speed, or you can use the 'cine' range and either compensate the ASA setting by 1/3, or you can apply a compensation of 0.3. All three methods should give the same result for all practical purposes. If you're shooting negative film then you really don't need to worry too much about such small exposure differences, even if you're shooting reversal film then 1/3stop isn't going to result in obvious over or under exposure. ...also don't forget that unless you set the K3 up with a strobe it is highly unlikely it will be running at 24fps, even when the speed dial is pointing to that setting - the calibration on my K3 was out by a significant amount!


If you haven't used the meter before then you may care to check its meter readings with some reversal stills film. If you search the internet you'll find a lot of opinion that Sekonic factory calibrate to something other than 18% reflectance. If you go out on a clear sunny day and apply the "sunny 16" rule you may find you need to apply a 'calibration offset' to the meter to achieve exposure results you're happy with. I haven't got mine to hand at the moment, but I think it has a permanent offset of something like 0.6 of a stop overexposure from the meter's 'default' reading.

The L-358 user instructions are available online. Page 26 shows how to apply a permanent "calibration compensation" (turn on the meter whilst holding down both "ISO1" and "ISO2" buttons, then adjust with the jog wheel). If you wish to set an 'exposure compensation' (which gives an indication on the screen that the displayed reading is adjusted from 'normal') then with the meter already turned on hold down both the ISO buttons and adjust with the jog wheel.

Edited by Ian Cooper, 16 January 2009 - 03:26 AM.

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#7 Taylor Magyar

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Posted 16 January 2009 - 09:34 AM

Ian, thank you so much- I think this is one of those cases where the obvious was eluding me because it was right in front of me. Somewhere along the line I blurred the fps and shutter speed concepts (breaking them into different, rather than similar concepts). Your affirmation in addition to my old 35mm slr books helped me out of this! I really appreciate everyone's quick and helpful replies. I've been lurking here for a while but as I dedicate my time to film more often now- I will try to contribute to this invaluable resource! Thanks Again!
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