Light Meter Settings K3 150 Deg shutter?
Posted 15 January 2009 - 05:05 PM
Posted 15 January 2009 - 07:56 PM
8 = 1/20
12 = 1/30
16 = 1/40
24 = 1/60
32 = 1/80
48 = 1/120
frame = 1/30
Posted 15 January 2009 - 11:13 PM
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.
Posted 15 January 2009 - 11:44 PM
Posted 16 January 2009 - 12:06 AM
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.
Posted 16 January 2009 - 09:34 AM