? about shutter speed

[Kevin Lewis]

From what I understand, the shutter spped on the XHa1 should be set to at least 100 to avoid flickeing under certain types of lighting. Can someone give more input on this. I have used this camea for almost two years now and I typcaaly shoot with a shutter spped of 60 and I have never had a problem. I have alwasy uded tungsten lighting. Is this something more likely to happen with florecents? I have also filmed in many office building that had florecents and still have not had a problem. Thoughts?

[Jay West]

Bear in mind that folks at DVinfo are from both NTSC- countries and PAL countries. In NTSC land, electrical power is delivered at 60 Hz, which means flourescent lights flicker 60 times per second. (Also, that's why electrical hum here is sometimes called "60 cycle hum.") In PAL countries, power is delivered at 50 Hz. Flourescents there will flicker at 50 times per second.

When shooting under flourescent lights, you can avoid flicker by using a shutter speed that is either the cycle rate or a multiple of it.

In Philadelphia where you shoot, you shoot at 1/60th (at least, that always seemed to be the default setting on my XHA1.) That is why 1/60 has been fine for you. If that shutter speed is too slow and you are getting (and want to avoid) motion blur, you go up to 1/120th. I do that with some of the dance recitals I shoot.

If you take your NTSC camera to a PAL country, set your shutter speed to 1/100th and that avoids seeing much 50 cycle flicker from lighting

From what I understand about PAL shooters preferring a 1/100th shutter speed, I gather that 1/50th may be a tad too slow, giving too much motion blur.

[Kevin Lewis]

So does that mean that lf I am in the USA, I dont have to worry about this as it relates to the flickering lights? Also, If I bump up the shutter speed to 100, is there anything else that I need to take into consideration other than the need for more light?

[Jay West]

Yes, mostly.

You need to look at the viewscreen. Every once in a while, you may run into some peculiar lighting situation If you see flicker, adjusting shutter speed can help solve the problem. I cannot come up with a specifc rule on this other than trying to get the opportiunity to test settings out beforehand and reviewing them.

Another place where I've fiddled with shutter speed is in doing 8mm film transfers for people. I've got projectors that allow me to adjust their speed. By setting the XHA1 on a 1/30 shutter speed (or een going to 24F with a 1/24th shutter speed) and varying the speed of the proejctor, I can usually eliminate all flicker. (As with line voltahe flicker, you are trying to come up with a matching combination fo frame rate/flicker rate and shutter speed.).

As for "more light" you can use shutter priority mode (TV mode on the big dial on the XHA1) or go fully manual (M mode ont he big control dial) and adjust iris and gain as needed after picking your shutter speed. Personally, I try to avoid using H gain because I find the resulting footage too grainy. I prefer motion blur to grain when I have a choice.

[Chris Soucy]

Originally Posted by Jay West

In NTSC land, electrical power is delivered at 60 Hz, which means flourescent lights flicker 60 times per second.

Wrong!

In PAL countries, power is delivered at 50 Hz. Flourescents there will flicker at 50 times per second.

Wrong!

When shooting under flourescent lights, you can avoid flicker by using a shutter speed that is either the cycle rate or a multiple of it.

Sorta wrong!

Back to basics.

A mains frequency of 60 Hz means just that, it cycles from a positive phase to a negative phase once every 1/60 th of a second.

Flourescent lights fire on both positive and negative phases of the mains cycle, thus, on a 60 Hz system, they fire 120 times per second.

On a 50 Hz system, they fire 100 times per second.

During those firings, flourescent and other gas discharge lighting exhibit a marked change of colour balance as they ramp up/ down.

Thus, shooting at high shutter speeds is not recommended whatsoever.

Now, introduce a video camera.

In an NTSC country, the shutter speed dial will have it's settings at multiples/ denominators of that mains frequency, 1/15; 1/30; 1/60 etc etc etc.

In a PAL country, it will be set to:

1/25; 1/50; 1/100

Because of clock drift on both the camera and the mains themselves, it is always advisable to allow one (1) complete positive/ negative cycle to occur during every frame of video.

This gives a "safe" shutter speed for 60Hz mains to be 1/60 of a second, 50 Hz, 1/50 of a second.

Any faster than that and you will find you're not getting a complete cycle, and will experience colour banding across the video.

Go really fast (why would you in low light?) and it gets horrendous.

This doesn't leave a lot of room for manouver in low light, but that's the deal with video, it's just that simple.


CS

[Jay West]

Chris, thanks for the clarification about the relationship between mains power frequency and flicker rates. I had the basic idea of the relationship between mains frequency and desireable shutter speeds but I certainly had misunderstood that flourescents and gas discharge lights were firing at double the mains frequency rate.

So, for the OP, even though my understanding was a bit off, the simple rule of thumb remains that it is best to use a shutter speed under flourescents that matches mains frequency: 1/60 for 60Hz mains and 1/50th for 50 Hz mains.

But for me, who misunderstood how flourescents actually work, I'm wondering if I've misinterpreted a couple of other points.

First, Chris, I'm not sure I correctly understood your point about "really fast" shutter speeds. Clearly, nobody should be trying to shoot 1/250th with an XHA1 under dim flourescent lighting. But, you are not saying that 1/100th in the "too fast" category, are you? Am I correct that you are saying only that 1/100th is not as safe as 1/50th in longer clips where there is time for the camera and mains clocks to diverge?

Second, have I correctly stated that 1/100th is acceptable when using an NTSC cam under florescentls in PAL land?. When shooting NTSC 1080i, the XHA1 does not give you an option for a 1/50th shutter speed but it does allow 1/100th. So, that seems like the only choice when taking an NTSC cam under flourescent lighting in 50 Hz countries. A friend of mine, who recently took a trip through south Asia and Australia, followed my advice to use 1/100th shutter speed for flourescent lighting. When he showed his footage on a large screen tv, I did not notice any any flicker or color banding. My friend told me his hosts were also shooting 1/100th shutter speeds with their PAL cam. Is this a case where I gave the right advice with incomplete facts or were these folks just inexplicably lucky?

Third, I should clarify that my mention of using higher shutter speeds (i.e., 1/120th) with a dance recital under NTSC-land flourescents, was not a low light situation. The room was very brightly lit with both ceiling lights and daylight from a long wall of windows. At rehearsal, with the shutter speed set to 1/60th, I got a lot of motion blur with the dancers. I found motion blur was less noticeable at 1/120th and the flourescent flicker was still absent, so that is what I used for the shoot. That said, all the clips were in the 3 to 5 minute range. Probably too short for noticeable clock drift to occur.

Fourth, when shooting longer clips under flourescents at 1/100th in PAL land or 1/120th in NTSC land, will running the camera off mains power (instead of battery) avoid clock drift?

[Chris Soucy]

Going to the last question first:

Nope, the camera clock does it's own thing as it will, the mains frequency does ditto and runing the camera of a mains supply doesn't help as the output of the adapter is DC, so no clock to lock to.

The problem with going above half the firing rate is simple.

If the shutter "opens" at exactly the start of a firing cycle at 1/120 (or 1/100 PAL) it will get the full colour gamet from that cycle, as it goes through the various colour shifts.

Where it goes down the pan is if it "opens" just past the peak of a firing cycle and follows it up the slope of the subsequent one, both of which are colder/ greener than at the peak.

It's not always a killer, depends on the lights and the camera, but it's getting "out there" for trouble.

Keep the shutter speed to twin cycle and it all averages out over two complete fires, no problem, except for the blur issue.

HOWEVER: Think of the poor bastards that are shooting 24p in that situation and are having (I use that word advisedly) to use 1/48!

Blur! Nothing but.

HOWEVER: All the great movies made at 24p with film, used incandescent lighting which doesn't flicker, so one problem solved.

Doesn't solve the blur problem which is, in fact, not a problem, as thousands of millions of bums on seats at cinemas can attest to, never hear a mutter about blur.

Yet, look at a single action frame from any movie shot on film and it's nothing but blur, pure and simple.

The only time it isn't, it's practically motionless and as clear as water. The brain is an amazing differential device and simply swallows the blur as inherrent to the story, which is far more important.

As for using 1/100 with an NTSC cam in a PAL country, well, what choice do you have? None, really.

If you don't go for a multiple you're in real trouble (1/48 being a particular one) but it's most probably survivable.

Lots more I could add but to keep this simple, I'll shut up right now.


CS