Can’t get to 180 degree shutter, is it worth getting closer?

timmytooltime · Sep 5, 2022

Hi folks,

I have a 3-5 stop vnd for my iPhone 12 Pro and it often doesn’t cut enough light to get me down to a 180 degree shutter angle. Is it worth lowering the shutter as much as possible to get as close to a 180 degree shutter angle or not bothering if I can’t get down that low?

I film in 25p mostly, so I’m aiming for 1/50. Is it worth bringing it down to say 1/400 or 1/200 or should I not bother if I’m still 2-3 stops over and just leave it in auto with no nd?

Thanks in advance,

Tim.

Andrew S10 · Sep 6, 2022

I've never run a test cycling through the shutter speeds with video, but when I shoot stills, I set my shutter speed to at least to 1/100th of a second to freeze the action, so I think anything above 1/80th won't have much motion blur.

I notice when there's little to no motion blur, and it bothers me, but that may or may not be the case for you or your viewers.

Are you using an app like Filmic Pro that gives you manual control?

I ask because, I'm wondering it your phone is erroneously defaulting to a higher ISO and shutter speed than it needs to.

Markr041 · Sep 6, 2022

timmytooltime said:
Hi folks,

I have a 3-5 stop vnd for my iPhone 12 Pro and it often doesn’t cut enough light to get me down to a 180 degree shutter angle. Is it worth lowering the shutter as much as possible to get as close to a 180 degree shutter angle or not bothering if I can’t get down that low?

I film in 25p mostly, so I’m aiming for 1/50. Is it worth bringing it down to say 1/400 or 1/200 or should I not bother if I’m still 2-3 stops over and just leave it in auto with no nd?

Thanks in advance,

Tim.

Ok, I'll ask it. If you are concerned about depicting motion well, why not shoot at 50 fps? Then high shutter speeds will NOT result for the most part with bad-looking motion. You can leave shutter speed on auto and not have to worry,

Off The Mark · Sep 7, 2022

timmytooltime said:
I film in 25p mostly, so I’m aiming for 1/50. Is it worth bringing it down to say 1/400 or 1/200 or should I not bother if I’m still 2-3 stops over and just leave it in auto with no nd?

timmytooltime · Sep 11, 2022

Thanks for the reply Andrew.

Yes, I use Filmic Pro, which gives me manual control and the ability to lock the ISO at ISO33, but on bright days I find this is still not enough with 5 stops of ND that is the max my filter provides.

Most of what I shoot is fairly slow paced, with movement in the scene from people walking, trees swaying, etc, so 1/200th does cut out almost all motion blur, apart from the odd car going past, so I think you’ve answered my question.

Thanks for that!

timmytooltime · Sep 11, 2022

Thanks for the reply Mark.

I did think of that, but as the footage will be a smaller component for a video shot mostly in 25p by a camera where I can get the footage shot at 1/50, I’d kinda dismissed it for a couple of reasons. Firstly, it’s a slow paced doco style vid, so will look more natural to me in 25p and secondly I’m often at 1/200 or 1/400 at the time of day/location I’m filming so I’d still wouldn’t be down to 1/100 anyhow to keep the 180 rule in 50p.

Thanks for your comment though, I do appreciate it.

timmytooltime · Sep 11, 2022

Thanks for the link.

Markr041 · Sep 11, 2022

timmytooltime said:
timmytooltime wrote:

Thanks for the reply Mark.

I did think of that, but as the footage will be a smaller component for a video shot mostly in 25p by a camera where I can get the footage shot at 1/50, I’d kinda dismissed it for a couple of reasons. Firstly, it’s a slow paced doco style vid, so will look more natural to me in 25p and secondly I’m often at 1/200 or 1/400 at the time of day/location I’m filming so I’d still wouldn’t be down to 1/100 anyhow to keep the 180 rule in 50p.

Thanks for your comment though, I do appreciate it.

You missed the key point: at 50 fps you no longer need to obey the 180 rule. Motion will look smooth at much higher shutter speeds, yes, 1/400th etc.

John Vickers · Sep 12, 2022

timmytooltime said:
Thanks for the reply Mark.

I did think of that, but as the footage will be a smaller component for a video shot mostly in 25p by a camera where I can get the footage shot at 1/50, I’d kinda dismissed it for a couple of reasons. Firstly, it’s a slow paced doco style vid, so will look more natural to me in 25p and secondly I’m often at 1/200 or 1/400 at the time of day/location I’m filming so I’d still wouldn’t be down to 1/100 anyhow to keep the 180 rule in 50p.

Why shoot at 25P/50P ?

Do you already have 25P footage? (In which case stick with that)

Otherwise, unless you are shooting for TV broadcast, and the broadcaster wants 25P, shooting at 29.94P, with a shutter speed equal to the local mains frequency, is likely the best solution for most people. Because 29.94P usually minimises motion judder on computer/tablet/phone displays.

timmytooltime said:
it’s a slow paced doco style vid

Then, if there's little fast movement, any frame rate from about 15fps up, and any shutter speed should be fine. Then "slow paced" does not necessarily mean a lack of movement within a shot.

timmytooltime · Sep 20, 2022

Much of the footage is already shot in 25p, so I’m kind of locked in in that regard, but I’ll definitely keep that in mind for next time.

timmytooltime · Sep 20, 2022

Sorry Mark, I don’t follow, why wouldn’t I have to follow the 180 rule if I was shooting 50p?

I was actually thinking if I shot in 50p and was using it in a 50p timeline for normal speed footage I’d have to shoot at 1/50th, rather than faster shutter speeds.

Markr041 · Sep 21, 2022

timmytooltime said:
Sorry Mark, I don’t follow, why wouldn’t I have to follow the 180 rule if I was shooting 50p?

I was actually thinking if I shot in 50p and was using it in a 50p timeline for normal speed footage I’d have to shoot at 1/50th, rather than faster shutter speeds.

Because at the high frame rate motion is captured smoothly and you don't need motion blur to gjve the illusion of smoothness. So, even high shutter speeds are ok. Try it and see for yourself.

John Vickers · Sep 21, 2022

timmytooltime said:
Much of the footage is already shot in 25p, so I’m kind of locked in in that regard, but I’ll definitely keep that in mind for next time.

Err, when I wrote "29.94P", I meant "29.97P". Doh!

I watch quite a lot of 25P stuff - mostly panel discussions or lectures - on a 60P computer display, and motion doesn't look weird. Maybe if someone was gesticulating a lot it would look odd sometimes.

The part about a "shutter speed equal to the local mains frequency" is important, unless you are sure there are no uncontrolled, flickery, lights near your shoot.

More precisely, you want a shutter speed that:

Divides the local mains frequency: i.e.. 1/50, 1/25, ... in most places outside the Americas.
If (1) is not possible, divides twice the local mains frequency: e.g. 1/100, 1/33.3, ... in most places outside the Americas.

Say you're shooting in daylight on a city street. It would not be surprising to have parts of building interiors, such as shops and offices, lit by lighting flickering at 2x and/or 1x mains frequency in shot. Which could be quite distracting on playback, even if they're on the edges of the shot.

To a degree, the "180-degree rule" is a myth. Many classic movies were shot on cameras incapable of shooting at 180°, because of the mechanical constraints of very accurately advancing the film between frames. And many classic US movies were shot at 144° (1/60 s at 24fps) to minimise flicker from streetlights, building lights, sporting event lights, and even studio lighting, such as early HMIs.

Some folks who should know better have claimed - and continue to claim - that frame rates that divide mains frequency eliminate mains-related flicker. That would only be true if the mains electrical supply was genlocked to the camera.

But in recent years, lighting flicker has become less of a problem, as LEDs have replaced gas-discharge lamps, and some jurisdictions - notably the EU and California - have introduced legislation to limit lighting flicker in new installations, for health reasons.

John Vickers · Sep 21, 2022

timmytooltime said:
Sorry Mark, I don’t follow, why wouldn’t I have to follow the 180 rule if I was shooting 50p?

I was actually thinking if I shot in 50p and was using it in a 50p timeline for normal speed footage I’d have to shoot at 1/50th, rather than faster shutter speeds.

As Mark says, as the frame rate goes up, the shutter speed increasingly becomes a free choice.

That's also true as the movement within a frame-time goes down. For example, if you are videoing a snail race:

- Subject to any potential flicker problems, as mentioned earlier.

John Sheehy · Sep 22, 2022

John Vickers said:
Some folks who should know better have claimed - and continue to claim - that frame rates that divide mains frequency eliminate mains-related flicker. That would only be true if the mains electrical supply was genlocked to the camera.

Are you mixing two different issues? Synchronization would be necessary only if the exposure time was much shorter than the lighting cycle period; if the exposure time is exactly the lighting cycle period or light flicker period, then it does not matter at all what part of the wave the exposure begins at, because an entire wave period will be recorded, and exposure is therefore the same in all frames.

John Sheehy · Sep 22, 2022

Markr041 said:
timmytooltime said:

Hi folks,

I have a 3-5 stop vnd for my iPhone 12 Pro and it often doesn’t cut enough light to get me down to a 180 degree shutter angle. Is it worth lowering the shutter as much as possible to get as close to a 180 degree shutter angle or not bothering if I can’t get down that low?

I film in 25p mostly, so I’m aiming for 1/50. Is it worth bringing it down to say 1/400 or 1/200 or should I not bother if I’m still 2-3 stops over and just leave it in auto with no nd?

Thanks in advance,

Tim.

Click to expand...

Ok, I'll ask it. If you are concerned about depicting motion well, why not shoot at 50 fps? Then high shutter speeds will NOT result for the most part with bad-looking motion. You can leave shutter speed on auto and not have to worry,

Ideally, we'd be capturing at hundreds of frames per second and deciding what to do with them in post. If you shot at 360fps, you could use ~1/360 shutter speed which would offer stable still extraction, and the ability for you to choose any slow-cadence shutter angle by dropping frames and adding the rest. Unless there is strobing close to half the framerate (around 180Hz on a 360fps capture), the editing capabilities would be virtually analog, temporally. 60 or 50 cycle strobing would not be an issue.

Of course, technology is not there yet in making this practical for most of us, as most high framerates in affordable, easily portable cameras take quality-sacrificing liberties like line-skipping, and/or are very low-res.

John Vickers · Oct 13, 2022

John Sheehy said:
John Vickers said:

Some folks who should know better have claimed - and continue to claim - that frame rates that divide mains frequency eliminate mains-related flicker. That would only be true if the mains electrical supply was genlocked to the camera.

Click to expand...

Are you mixing two different issues?

Could you explicitly state what "two different issues" I am mixing?

John Sheehy said:
Synchronization would be necessary only if the exposure time was much shorter than the lighting cycle period;

The word "much" is doing some heavy lifting.

Also "much shorter than" should be "much different from". "Significantly different from" would be better. We could then go on to quantify "Significantly", for a given light source.

For light sources that have bounded, continuous output, for small differences in exposure time from a period of the light output, the recorded banding/flicker (in linear light) is proportional to the error in the exposure time relative to the period. [The assumption of bounded continuous output is not necessary. The output does not even need to be a function. It is sufficient for the integral of the output over any bounded time interval to exist. We could have lighting like HSS flash.]

Assuming we have synchronisation between the frame cycle and the lighting flicker cycle, at a given point in the recorded images, there will be no flicker.

But unless we have global shutter, which is unlikely, different parts of the images will be exposed at different phases of the lighting cycle, so we can have stationary banding, even if we do not have flicker unless the exposure time is "very close" to a period of the light output. This is equally true in a film movie camera with a rotating shutter and in a CMOS sensor with row-by-row reset and readout.

In the unlikely case that we do have global shutter, the exposure in this genlocked case depends on the phase of the fundamental lighting period at which the exposure starts.

John Sheehy said:
if the exposure time is exactly the lighting cycle period or light flicker period, then it does not matter at all what part of the wave the exposure begins at, because an entire wave period will be recorded, and exposure is therefore the same in all frames.

Yes.

But the exact case is uninteresting for practical purposes.

Mains frequencies vary with the load on the power grid. Exposure times are not always clear: if we ask for a nominal 1/60 s, do we get 1/60.00 s, or 1/64.00 s? Does it depend on whether the camera is capturing stills or video? Whether we are shooting on Nikon or Panasonic?

What is interesting is: How small do the errors need to be to assure acceptable results?

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Can’t get to 180 degree shutter, is it worth getting closer?

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