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Sekonic L-758cine and Shutter Speed


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#1 Drew Maw

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Posted 19 February 2010 - 05:22 PM

Hey guys,

I've been trying to figure out how to use Shutter Speed, opposed to Shutter Angle on my Sekonic L-758cine in cine mode (i.e. f/s mode). I know the Spectra IV does it. Does the L-758cine do it? It's difficult to figure out the calculations from angle to speed. I've been shooting on the Canon 7D and RED ONE, and sometimes I like to shoot at a super fast shutter speed if the director wants it. Thanks!

Drew.
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#2 Dimitri Zaunders

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Posted 19 February 2010 - 08:47 PM

I'm not sure if this helps but you can always dial in an exposure time of 1/30, 1/60th etc by scrolling the jog wheel down through all of the lower frame rates until it switches to fractions of a second.

And if you want to be able to adjust exposure time in fewer increments you can adjust the custom settings to display 1/3 or 1/2 step increments.
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#3 Drew Maw

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Posted 19 February 2010 - 08:59 PM

I'm not sure if this helps but you can always dial in an exposure time of 1/30, 1/60th etc by scrolling the jog wheel down through all of the lower frame rates until it switches to fractions of a second.

And if you want to be able to adjust exposure time in fewer increments you can adjust the custom settings to display 1/3 or 1/2 step increments.


I'm not sure that helps me. I want to be able to keep my framerate adjustable, I shoot at 24fps or 40-60fps and 120fps, especially for commercial work. Am i wrong, or am I missing something?
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#4 Dimitri Zaunders

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Posted 19 February 2010 - 09:20 PM

Hey Drew,

I'm not familiar with the adjustable shutter speed settings on the 7D or RED cameras so I'm probably not much use.

But as I understand it 'shutter speed' is a function of frame rate and shutter angle which can either be calculated automatically by the Sekonic when you input those two values, or manually when you decide on an exposure time of 1/50th, 1/60th etc. As far as I know those are the only two ways to set exposure times on any lightmeter, including the 758c.

Anyway I could very likely be wrong so it's probably better to let one of the forum's pros answer this question instead!
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#5 Drew Maw

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Posted 20 February 2010 - 12:23 AM

Hey Drew,

I'm not familiar with the adjustable shutter speed settings on the 7D or RED cameras so I'm probably not much use.

But as I understand it 'shutter speed' is a function of frame rate and shutter angle which can either be calculated automatically by the Sekonic when you input those two values, or manually when you decide on an exposure time of 1/50th, 1/60th etc. As far as I know those are the only two ways to set exposure times on any lightmeter, including the 758c.

Anyway I could very likely be wrong so it's probably better to let one of the forum's pros answer this question instead!


Yeah, I'm aware of the ability to input shutter speed, but you have to choose between shutter speed OR f/s, but you can't do both at the same time, or at least to my knowledge, but that's what Im trying to figure out how to do. I mean the 758c allows you to adjust the shutter angle when on f/s, but of course you lose the shutter angle function when you've adjusted from f/s to shutter speed, but it's not making sense why I can't have f/s and shutter speed at the same time.
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#6 Dimitri Zaunders

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Posted 20 February 2010 - 01:52 AM

Yeah, I'm aware of the ability to input shutter speed, but you have to choose between shutter speed OR f/s, but you can't do both at the same time, or at least to my knowledge, but that's what Im trying to figure out how to do. I mean the 758c allows you to adjust the shutter angle when on f/s, but of course you lose the shutter angle function when you've adjusted from f/s to shutter speed, but it's not making sense why I can't have f/s and shutter speed at the same time.



Well until another person steps in here then it's just the blind leading the blind... (if you'll pardon the expression)

My understanding is that because:

shutter speed = fps x shutter angle (as a fraction)

then there would be no benefit to being able to simultaneously adjust both of those values in the lightmeter. The meter only needs to know an exposure time so that it can give a reading, and besides shutter speed and fps are tied together into that direct relationship so changing one will always change the other. You would never be able to input both values separately as they will always affect each other.

Anyway that's just my understanding of the theory behind it, but I've never encountered this situation in the real world so maybe I'm missing something. Can you give an example of a time when you'd need to input both of these settings?
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#7 Drew Maw

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Posted 20 February 2010 - 03:33 AM

Well until another person steps in here then it's just the blind leading the blind... (if you'll pardon the expression)

My understanding is that because:

shutter speed = fps x shutter angle (as a fraction)

then there would be no benefit to being able to simultaneously adjust both of those values in the lightmeter. The meter only needs to know an exposure time so that it can give a reading, and besides shutter speed and fps are tied together into that direct relationship so changing one will always change the other. You would never be able to input both values separately as they will always affect each other.

Anyway that's just my understanding of the theory behind it, but I've never encountered this situation in the real world so maybe I'm missing something. Can you give an example of a time when you'd need to input both of these settings?


Example: when shooting on the RED ONE, or Canon 7D, or any prosumer camera like the HVX200 or the Sony EX series, including cams like the Sony F900, F23, F35, and the Panavision Genesis, etc, etc, pretty much any digital camera, you can adjust the frame-rate and the shutter speed separately. The frame-rate can be 24, while the shutter can be 1/60 or 1/125 or all the way up 1/2000th of a second. Similarly, you can also have a frame-rate of 120, or 60, and then choose different shutter speeds as well. Shutter speed and shutter angle are the same thing. Shutter speed is just a digital measurement (sensor refresh rate) for a new technology (digital sensor), whereas shutter angle is an analog measurement (a spinning adjustable disc) for an analog technology (film). So, your understanding of shutter speed is incorrect, whereby, shutter speed and fps are completely separate measurements that affect the final image differently.

Where are the pros!!?? We are seriously getting off track. I wasn't posting here to hold a workshop! Not that I don't mind teaching, but I've got a serious shoot (pilot) for MTV coming up!
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#8 Dimitri Zaunders

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Posted 20 February 2010 - 07:29 AM

Ah, makes sense. My old GL2 prosumer camera had a variable shutter speed but of course no variable frame rate.

Still, I think that as long as you take your lightmeter and dial in your shutter speed, the frame rate will be irrelevant. As long as the meter knows your exposure time it can determine an aperture setting; whether you tell it your shutter speed directly or feed it a combination of shutter angle and fps doesn't matter, as long as it knows one of these things.

By the sounds of it these cameras are effectively adjusting the 'shutter angle' automatically as you increase or decrease your frame rate, in effect compensating for the fps to maintain your chosen exposure time. Of course these digital sensors don't use a real shutter but the effect is the same: a variable shutter maintains a set shutter speed as frame rate changes.

Therefore my understanding is that you can disregard your frames per second and trust that the camera is delivering a set exposure time no matter the speed you're shooting at. So as long as you know your shutter speed (1/10th, 1/60th, 1/1000th etc) then you can put this value into the meter and start taking readings.


It would still be great if a forum regular came along and verified this though. Anyone...?
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#9 Dominic Gruenberg

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Posted 20 February 2010 - 08:13 AM

Hi,

I am no forum regular (apart from reading), but I do verify your thought, Dimitri. There's a simple reason why the Sekonic (I own one myself) isn't able to adjust framerate and shutter speed at the same time: there's no need. The framerate option is just another conversion from a shutter speed. 25 f/s is equivalent to a shutter speed of 1/50th of a second, 24 f/s is equivalent to a shutter speed of 1/48th of a second, and so on (assuming 180° angle shutter, of course). Coming to video, you don't need f/s anymore, you just take the shutter speeds. It doesn't matter if you're shooting in 24 f/s or 300 f/s, if you're shutter speed is 1/600th of a second, you expose for 1/600th of a second either way. so don't measure the f/s, just the shutter speeds, and you're safe.
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#10 Drew Maw

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Posted 20 February 2010 - 12:02 PM

Hi,

I am no forum regular (apart from reading), but I do verify your thought, Dimitri. There's a simple reason why the Sekonic (I own one myself) isn't able to adjust framerate and shutter speed at the same time: there's no need. The framerate option is just another conversion from a shutter speed. 25 f/s is equivalent to a shutter speed of 1/50th of a second, 24 f/s is equivalent to a shutter speed of 1/48th of a second, and so on (assuming 180° angle shutter, of course). Coming to video, you don't need f/s anymore, you just take the shutter speeds. It doesn't matter if you're shooting in 24 f/s or 300 f/s, if you're shutter speed is 1/600th of a second, you expose for 1/600th of a second either way. so don't measure the f/s, just the shutter speeds, and you're safe.



This is incorrect. The reason I say that it's incorrect, is because if I shoot at 24fps at 1/60th, and I have a keylight at f2.8, if I dial my fps to 60fps at 1/60th, then I'll read at f2.0 approximately, and if I change my shutter to 1/125, then my keylight will now read at f1.4. Again, the fps and shutter speed are independent of each other.
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#11 K Borowski

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Posted 20 February 2010 - 12:39 PM

If you are shooting with basically a digital stills camera, my understanding would be you'd METER it like a stills camera.

I.e. you'd disregard the framerate and use only the F/stop and shutter speed on the meter.


You're worrying about the individual frame exposures, after all.



One thing that worries me about deviating too far from a "normal" shutter speed with these new HD-DSLRs is that you don't have a spinning or even a leaf shutter, but something called a focal plane shutter.

I'd imagine if you get the shutter speed up too high, you'd run into some undesirable artifacts, not due to any particular flaw with focal planes, but merely their not being designed with motion capture in mind.
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#12 K Borowski

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Posted 20 February 2010 - 12:49 PM

E Shutter speed and shutter angle are the same thing. Shutter speed is just a digital measurement (sensor refresh rate) for a new technology (digital sensor), whereas shutter angle is an analog measurement (a spinning adjustable disc) for an analog technology (film). So, your understanding of shutter speed is incorrect, whereby, shutter speed and fps are completely separate measurements that affect the final image differently.


Where are the pros? What, do you expect someone with an ASC after their name to come running to your rescue?


Shutter speed and shutter angle are NOT the same thing. One is the angular speed of a shutter (in a real movie camera) as it spins in a circle. The other is the angle, in degrees that the shutter is open as it speeds by.

They COMBINE to provide an exposure in fractions of a second.

Anyway, it's best to use exposure in fractions of a second, not "shutter angle" or frame rate measurements because the latter is making an assumption that you have a camera with a shutter angle that isn't adjustable or conforms to the standard. I think the meters that give you exposures in frames per second just assume a 170° or 180° opening in the shutter, which isn't the case with all cameras.



But 7Ds, I assure you have REAL shutters too. They are "analog" if you want to call them that. Real shutters aren't a phenomenon confined to "analog" film.

They continue to be an important part of the exposure process. I know some cameras have virtual shutters or can shoot with the shutter open and just interpret increments from the sensor, but this isn't optimal and you almost always run into artifacts. Unless you're shooting at such a fast rate that movement across the frame within one frame's exposure becomes an issue real shutters continue to be the BETTER OPTION for controlling the time of exposure, and keeping blur down if need be.

But they aren't movie shutters, they are focal plane shutters. They don't spin, they flap open and closed. So you could conceivably get an artifact where one part of the frame is recording a discretely different moment in time than the other part at a high enough shutter speed.
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#13 Dominic Gruenberg

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Posted 20 February 2010 - 02:24 PM

This is incorrect. The reason I say that it's incorrect, is because if I shoot at 24fps at 1/60th, and I have a keylight at f2.8, if I dial my fps to 60fps at 1/60th, then I'll read at f2.0 approximately, and if I change my shutter to 1/125, then my keylight will now read at f1.4. Again, the fps and shutter speed are independent of each other.

Well, which part is incorrect? As I said, "24 f/s is equivalent to a shutter speed of 1/48th of a second [...] assuming 180° angle shutter". If you don't have a 180° shutter, as you do, you simply measure the shutter speed.
If you shoot with a shutter speed of 1/125th of a second, each frame will be exposed to light by 1/125th of a second. Each frame, meaning the 24 frames in one second, the 60 frames in one second, or 2 frames in one minute. It makes no difference if you shoot 24 f/s or 60 f/s. It's just a change of speed on how many pictures you are taking in one second, but there's no change in exposure.

Can it be, that you set your Sekonic to 24 f/s, measured f2.8, then set it to 1/60th of a second and measured f2.0? If so, that is because, as I said, the 24 f/s are measured with a shutter speed of 1/48th of a second.
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#14 Dominic Gruenberg

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Posted 20 February 2010 - 02:48 PM

Can it be, that you set your Sekonic to 24 f/s, measured f2.8, then set it to 1/60th of a second and measured f2.0? If so, that is because, as I said, the 24 f/s are measured with a shutter speed of 1/48th of a second.

Obviously that would be incorrect, the f-stop measured with 1/60th shutter speed should be only slighly lower than with 24 f/s, not one full stop...
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#15 K Borowski

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Posted 20 February 2010 - 03:12 PM

Obviously that would be incorrect, the f-stop measured with 1/60th shutter speed should be only slighly lower than with 24 f/s, not one full stop...


Yeah, that is 1/2 F/stop off, not a full stop.

Even 1/45 of a second and 1/48 of a second are actually the same thing. The former is rounded, the latter isn't.


There are a lot of roundings and conventions with F/stop, the ASA part of the ISO speed measurement, and shutter speed numbers to make them even.
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#16 Chris Millar

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Posted 20 February 2010 - 03:13 PM

Drew,

I own the lightmeter you are talking about, I own variable shutter angle and variable speed cine cameras and I own an EX1 and operate a RED on occasion. Not a 'pro' but I hope you'll trust me on this one and I'll throw in another cry of the (bleedin obvious!):

shutter speed = frame rate * (shutter angle/360)

shutter speed = actual exposure time

So you either plug in your fps into the (restricted :rolleyes:) options on the meter and make sure your angle is set correctly or wind it back all the way to the normal exposure times (shutter speeds) that youd shoot on a normal camera and work that way...

What you seem to want would infer that you dont know the frame rate your camera is running at and you want your meter to tell you - in effect becoming a calculator ... or, hmmm, what exactly do you mean by "f/s and shutter speed at the same time"?

As has been mentioned already - they are connected - it's like asking for a car with two steering wheels so you could steer in two directions.

Edited by Chris Millar, 20 February 2010 - 03:16 PM.

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#17 Chris Millar

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Posted 20 February 2010 - 03:23 PM

Shutter speed and shutter angle are the same thing.


No

But to add to the confusion: when a camera gives you the options of frame rate and then shutter speed, if you choose one and set it first (usually frame rate) but then modify the other (shutter speed) all you are actually doing is changing the shutter angle - but not because they are the same thing - but because they are interrelated by the equation that has been stated above. ;)
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#18 Drew Maw

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Posted 20 February 2010 - 06:31 PM

No

But to add to the confusion: when a camera gives you the options of frame rate and then shutter speed, if you choose one and set it first (usually frame rate) but then modify the other (shutter speed) all you are actually doing is changing the shutter angle - but not because they are the same thing - but because they are interrelated by the equation that has been stated above. ;)


Shutter speed and shutter angle are the same thing for different mediums, here's something from my site, sourced from another site: http://drewmaw.com/1...-shutter-angle/

Yes, I understand that a film camera's shutter can be adjusted via speed and angle, but on a digital camera, there is a sensor refresh rate, which translates to shutter speed. There is no spinning disc in a digital, obviously, but there is a SPEED in which the sensor refreshes, which is IDENTICAL to how a shutter disc/angle reacts to film exposing. While you're right, they aren't the same thing, they accomplish the same things.

Yes, with the RED and the 7D, you can adjust the frame-rate per second (aka f/s or fps) and independently, you can adjust the shutter speed (aka the speed at which the sensor refreshes every second), much like a shutter angle. From what it sounds like, I'll have to just keep translating angle to speed in my head, opposed to have the meter just switch from angle to speed (which would seem easy, which is what the Spectra IV does). Switching the L-758c f/s on the meter to shutter speed doesn't fix the problem. I"M NOT SHOOT STILLS. Yes, if I was shooting stills, then it wouldn't matter. I want to be able to set my FPS and Shutter SPEED separately, and no 1/48 DOESN'T EQUAL 24FPS (that's absurd). I have and like shooting 1/1000 shutter speed at 24fps.
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#19 Chris Millar

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Posted 20 February 2010 - 07:35 PM

Shutter speed and shutter angle are the same thing for different mediums, here's something from my site, sourced from another site: http://drewmaw.com/1...-shutter-angle/

Yes, I understand that a film camera's shutter can be adjusted via speed and angle, but on a digital camera, there is a sensor refresh rate, which translates to shutter speed. There is no spinning disc in a digital, obviously, but there is a SPEED in which the sensor refreshes, which is IDENTICAL to how a shutter disc/angle reacts to film exposing. While you're right, they aren't the same thing, they accomplish the same things.

Yes, with the RED and the 7D, you can adjust the frame-rate per second (aka f/s or fps) and independently, you can adjust the shutter speed (aka the speed at which the sensor refreshes every second), much like a shutter angle. From what it sounds like, I'll have to just keep translating angle to speed in my head, opposed to have the meter just switch from angle to speed (which would seem easy, which is what the Spectra IV does). Switching the L-758c f/s on the meter to shutter speed doesn't fix the problem. I"M NOT SHOOT STILLS. Yes, if I was shooting stills, then it wouldn't matter. I want to be able to set my FPS and Shutter SPEED separately, and no 1/48 DOESN'T EQUAL 24FPS (that's absurd). I have and like shooting 1/1000 shutter speed at 24fps.

Well, I think the issue is with the nomenclature involved...

Try this on for size: Sekonic are using a strict cine interpretation, you know, spinning chunks of metal and celluloid. That is how they work and until they take a close look at the way digital cine shutter and frame rate options are presented to the world (and thereby causing these headscratchers) you're just going to have to work with that. Consider yourself somewhat enlightened !
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#20 Dominic Gruenberg

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Posted 21 February 2010 - 04:48 AM

[...]Switching the L-758c f/s on the meter to shutter speed doesn't fix the problem. I"M NOT SHOOT STILLS. Yes, if I was shooting stills, then it wouldn't matter. I want to be able to set my FPS and Shutter SPEED separately, and no 1/48 DOESN'T EQUAL 24FPS (that's absurd). I have and like shooting 1/1000 shutter speed at 24fps.

Drew,

For the Sekonic L-758C (which, I state again, do own myself) 24 f/s equals 1/48th of a second exposure time (if it is set to a 180° shutter). That is not absurd, that is how it is. That is even said in the link you've given us.

If you want to shoot 24 f/s with a shutter speed of 1/1000th of a second, you have to set your light meter to 1/1000th of a second. Think about this: what is the difference in shooting 24 frames in one second with an exposure speed of 1/1000th of a second, or one picture in a minute with the same settings? You are rapidly shooting still images, in your case 24 images per second with an exposure speed of 1/1000th of a second.

I think you may got confused because of the whole shutter angle = shutter speed thing. An example: let's say we are shooting in 24 f/s with a film camera and a video camera. The film camera has a shutter angle of 180° (= 1/48th exposure time), the video camera has a shutter speed of 1/48. At this point the exposures of both cameras are the same. Let's change exposure times. The film camera gets a shutter angle of 45° which gives us an exposure of 1/192nd of a second). Hypothetically our video camera can change to that exact same exposure speed, so set it there. Again, both cameras record 24 f/s with an exposure speed of 1/192. And now we change the framerate, but don't touch the exposure settings. We set the film camera to 48 f/s. Because the shutter is now rotating twice as fast to capture twice as many frames per second, the exposure time is twice as fast as well, it is now 1/384th of a second. we set the video camera to 48 f/s, but don't change the exposure time. The video camera now records 48 frames per second with a shutter speed of 1/192nd of a second. So we changed framerates on both cameras, and only the exposure time on the film camera changed.

film: 24 f/s, 180° = 1/48
video: 24 f/s, 1/48 = 1/48

film: 24 f/s, 45° = 1/192
video: 24 f/s, 1/192 = 1/192

film: 48 f/s, 45° = 1/384
video: 48 f/s, 1/192 = 1/192

Hope I could clear things up a little.
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