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Shooting At 25fps In A 60Hz Country

class="Paragraph">Hello, An upcoming job requires 25fps shot in the States. The question is what is a flicker free shutter angle? 144 degrees? Someone has suggested 150 degrees, which isn't an actual setting, is it?

class="Paragraph">There will be xenon in the show and varilites, it's a concert music video . Also, what about going to 50fps?

class="Paragraph">Thanks,

class="Paragraph">Harry Dawson


class="Paragraph">Yes, 150° is to be used for 60Hz HMI at 25fps:
(1/25 s. x 150/360 = 1/60 s.)
144° is used to shoot NTSC CRT screens at 24fps:
(1/24 s. x 144/360 = 1/60 s.)

class="Paragraph">This shutter opening angle is available on XTRprod's and the latest SR-3's.


class="Paragraph" With intermittent sources (HMI, HTI, magnetic ballast fluorescent, etc) you can shoot 25 fps at 75 or 150 degree shutter. Xenon's are DC constant arc sources and will not flicker at any frame rate. The Varilites are probably HTI sources with magnetic ballasts so you WOULD have to pay attention, as you would with any of the non-incandescent theatrical follow spots EXCEPT for any of the Strong Xenon Super Troopers which are xenon, DC, and therefore non-flickering. If you are working off generator power, there is another thing that you can do.


Most 60Hz generators will not function at 50Hz properly (20% underspeed is to far from "home" for them) but they will almost always run at 62.5Hz...and at 62.5Hz, you can shoot 25 fps with impunity. I have not actually tried this myself, but the late Bernie Grubeman of Camera Mart NY convinced me of this back in 1980 or so and I have heard other people HAVE done it. I hope this is helpful information. Obviously if you can go to a lighting rental house that has Varilight's and shoot a short test this would be a GOOD idea.

class="Paragraph"
Mark


class="Paragraph">By the way, 150 degree shutter will work both for 25fps and for 50 fps.
At 25fps, 150 degree is 1/60th sec, 75 degree is 1/120th sec
At 50 fps, 150 degree is 1/120th sec.


class="Paragraph">Silly question but why not shoot at 24fps? The Americans do it all the time and then send their stuff over here for TX at 25fps.

class="Paragraph" Looks and sounds fine -

class="Paragraph" Shangara Singh.


class="Paragraph">Others told you that 150 degree shutter at 25fps is the way to go ...

class="Paragraph">BTW...150 degree shutter and 25 fps is also the _perfect_ combination to shoot NTSC monitors w/o having to sync. At that combination there simply isn't a roll bar ...

class="Paragraph">But, trying to get exactly 150 degrees can be a problem ...

class="Paragraph">While testing this combination with a Platinum Panastar I had better "luck" setting the shutter to 150 using the scribe marks on the back of the shutter itself (visible after pulling the movement) vs. using the digital shutter display. When I asked Panavision about it, the mechanical engineers said their marks were more accurate, while of course the electronics people said that their digital display _should_ have been more accurate ... ?

class="Paragraph">Arri says their digital display is completely accurate, however when we tried the test using a 535A and inputting the shutter angle via the CCU computer link, the test footage showed that something was slightly off ... ?

class="Paragraph">DP, Gary Thieltges (spelling ?) who seemingly "discovered" this combination because he shoots a lot of european commercials at 25 fps, apparently had Arri Burbank add a 150 degree "notch" to his camera(s).

class="Paragraph">If the shutter is slightly off, you will start to see a few white or black (depending in which direction its off) dots in a line in your footage. These are the beginning of the out of sync line forming. Certainly better then a solid line.

class="Paragraph">I don't know how exact the 150 degree shutter setting has to be for your application with lights ....

class="Paragraph">Even using the handy RCU control unit, you should be able to very accurately dial in 150 degrees with either an Arri 435ES or 535A camera.


class="Paragraph">Since the mirror shutter of the 535A and 435ES can be set to any value between 11.2 and 180 degrees, 150 degrees is not a problem on those cameras either.

class="Paragraph">Cheers,
Marc Shipman-Mueller, Technical Representative
Arriflex Corporation; 1646 N. Oakley Ave, Suite #2, Chicago, IL 60647-5319, USA


class="Paragraph" It seems to me that using an NTSC monitor to "calibrate" a variable shutter to achieve 150 degrees for 50 fps shooting in a 60 Hz world as described by Mako is a very accurate way to go, since you can see slight inaccuracies as "time drift" as a roll bar either moves up or down the screen. Wish I had thought of that as a test protocol.

class="Paragraph"
Mark


class="Paragraph">I still can't figure out why people going to the states shoot at 25fps and not 24fps when all the cameras that I know of (not so sure of the 16 BL, though) can shoot at either rate and the transfer facilities can t/f at 24/25fps.

class="Paragraph" Someone put me out of my misery, please - I keep hoping for a shoot in the states and, who knows, it may happen tomorrow so it would be good to know!

class="Paragraph" Shangara Singh.


class="Paragraph" Certainly dialog can be transfered off-speed , but if you are shooting sync music (eg. music video) material the speed difference is enough to change the speed of the song so that it would not cut from "25 for 25" and "24 for 25" shots...the music would speed up and slow down like an early cassette machine.

class="Paragraph"
Mark Weingartner


class="Paragraph" Mark H. Weingartner writes :

class="Paragraph"
>It seems to me that using an NTSC monitor to "calibrate" a variable shutter to achieve 150 degrees for 50 fps shooting in a 60 Hz world as described by Mako is a very accurate way to go

class="Paragraph">Good idea, but remember you'll have to wait for the lab to process what you shoot because your eye won't see the same thing through your finder.

class="Paragraph">John Duclos
Technical Manager - Arri Media


class="Paragraph" In terms of phasing, of course,you can't see what you will get, but in terms of speed, you should be able to see the roll bar going one way or the other in the viewfinder ...if it isn't moving up or down the frame you have the right shutter angle/speed combo.

class="Paragraph"
Since all you need in order to avoid flicker with the lighting fixtures is the right speed/angle combo as opposed to the additional issue of phase when actually shooting monitors or rephotographing film, it seems to me that you would be home free. Having said that, I think I need to run down to Clairmont or somewhere and borrow a body and a monitor to test my cockamamie theory.

class="Paragraph">Mark Weingartner


class="Paragraph" Dumb question, but aren't you really calibrating it to 59.94 then? I mean, plenty close, and a great clever idea -- but not 60Hz? Actually, better than 60Hz if you are shooting monitors...


class="Paragraph">I was wondering if anyone would bring that up...I think you would be close enough for lights, but I'm not sure without testing...I guess the whole issue is how to set a variable shutte accurately to 150 degrees...we have to assume that a crystal motor driven at 25fps will actually be running at 25fps (remember when sound men all carried P.O.M's?)


class="Paragraph">I'll be at Otto Nemenz tomorrow anyway. I'll try playing with my 435 at 25 fps, a monitor and the RCU plus and minusing around 150 degrees through the finder and the gate

class="Paragraph">Cheers ...

class="Paragraph">Mako


class="Paragraph">Oh, darn! I would invite myself along to see what happens but I will be in the GREATER PACOIMA METROPLEX in 8 perf purgatory...Please let us know what you discover
Mark


class="Paragraph">Try it, Mark, and you'll find that 25fps and 150 degrees on an NTSC monitor will not give you a stationary roll bar. What it does give you is 1/60 second exposure time (one field of video) on film only.

class="Paragraph">Your eye gets its image from the 180 degree, fixed segment of mirror on the shutter which =1/50 second. This will appear as a rolling, bright band running through the screen.

class="Paragraph">John Duclos
Technical Manager - Arri Media


class="Paragraph" Does anyone still rent P.O.M.'s? I don't recall, but if there were a setting that cycled the LED's at 60 Hz, you could check your shutter that way, but since the device was designed to check speed for reference to sound, I suppose it only cycles with respect to 24 frames or 25 frames, not necessarily 50Hz or 60Hz. Any one know ?

class="Paragraph"
Mark


class="Paragraph">Ideal frame rate/shutter angle for 60 cycle fluorescent tubes is 24fps/144 degrees (or 30fps and 180 degrees or 33.33 fps and 200 degrees), but we regularily get away with filming normal fluorescent tubes at 24 fps at 180/200 degree shutters.

class="Paragraph">At 25 fps the ideal shutter is 150 degrees. But if your camera can't be set for 150 degrees (SR3) are you going to be O.K. at 25fps and 180 degrees? Would that be better then 25 fps at 144 degrees ... ?

class="Paragraph">Wouldn't it be better to have two pulses plus (180 degrees) rather then not getting atleast 2 pulses (144 degrees)?

class="Paragraph">Can anyone predict how bad the fluorescent flicker will be if you can't film at 25 fps and 150 degrees .... ?


class="Paragraph">I had a film test done at a rental house on friday to test filming an NTSC TV source at 150 degree and 25 fps. Supposedly with this combination one should not have to do any phasing since their should be _no_ scan line.

class="Paragraph">Looking through the camera (Arri 435ES/180 degree mirror) viewfinder and through the aperture gate (pressure plate removed, "magic" frosted "scotch" tape over the aperture to act as a ground glass) at a TV monitor receiving an over the air signal with the camera running at 25 fps and at and around 150 degrees revealed a rolling soft edge dark diagnol band.

class="Paragraph">A call was made to DP Gary Thieltges (who "discovered" this shutter/fps combination) who said yes you will see this band but it won't photograph ...(?!)

class="Paragraph">Apparently there will be a thin scan line every 7th (8th?) frame but it won't be noticable during normal viewing.

class="Paragraph">The monitor was filmed at 25 fps/150 degrees and at 25 fps with the shutter being slowly changed between 148 and 152 degrees with the RCU control unit in the shot so that the degree settings will be visible in the footage.

class="Paragraph">A 25 fps test was also shot with a MovieCam SL since it has a mechanical indent for 150 degrees.

class="Paragraph">We don't know if the resolution of the Arri RCU display is accurate enough to set at 150.15 degrees. This would be the actual shutter angle needed at 25 fps with the NTSC monitor scanning at 59.94 cycles. (shutter angle = frame rate times 3 times 2.002 "pulses"/exposure cycle)

class="Paragraph">Can a mechanical shutter indent be made accuarately and practically at 150.15 degrees ... ?

class="Paragraph">The transfer will be done on Monday and hopefull we can post the results on Tuesday when I get back into town from my location shoot.

class="Paragraph" Since this thread was started by a question concerning shooting in the US at 25 fps for the European market, it was interesting to see a 9 camera prep taking place at the same rental house, for concert footage being shot here for Europe.

class="Paragraph"
The cameras are going to run at 25 fps and 144 degree shutter.

class="Paragraph">The question is why 144 degree shutter? With this combination the DP must be using tungsten [or square wave HMI's ?] [it's indoors] light ... but then why not have the shutters set a 180 degrees for maximum through put? Maybe he wants that minimal amount of extra strobbing/extra sharpness?

class="Paragraph">The nine cameras are Arri SR3's, whose shutters can not be set to 150 degrees. There will also be one Aaton XTR (whose shutter can be set at 150 degrees) as the "A" crane camera w/ 800' mags.


class="Paragraph">I haven't seen the footage/transfer myself but I talked to the techs at Otto Nemenz Int. camera rental house in Hollywood who kindly shot our 25fps/150 degree test of a NTSC monitor.

class="Paragraph">The footage taken with the Arri 435ES at 25 fps/150 degrees was almost perfect. After repeated close up viewing of the transfer one could make out the very slight beginnings of a line - a string of dots.

class="Paragraph">The footage where they slowly altered the shutter angle from about 148 to 152 degrees showed a constantly changing (in width) line that disappeared at about 150 degrees and then immediately reappeared. Apparently the way they photographed the RCU display made it difficult to see the read out.

class="Paragraph">The footage taken with the MovieCaM SL with it's shutter set to a mechanical indent of 150 degrees showed a very obvious bar.

class="Paragraph">They are going to redo the test using a number of different 435 bodies and now setting the shutter to 150.1 and 150.2 degree. The RCU does not allow a setting of 150.15, which is the "perfect" shutter angle for 59.94 scan.

class="Paragraph">We've found that the removing the bar completely requires an extremely precise shutter, but that perhaps the electronically inputted shutter angle with the 435/535 family of Arri cameras is accurate enough to allow filming of NTSC monitors without any phasing.

class="Paragraph">The mechanical indent on the MovieCams are not accurate enough to allow using this "emergency" procedure.

class="Paragraph">I'll keep everyone posted on any further tests


class="Paragraph">I'd like to publicly send Mako an enormous thank you for this information.

class="Paragraph">I've already made use of it.

class="Paragraph">I'm shooting a commercial for a chain of computer stores at the moment.

class="Paragraph">My biggest problem on the main store location was that I had to use the florrie fittings, they're well featured in shot, the roof is a suspended one and it wouldn't support the weight of the 72 Kino Flo 4' 4banks I would have to use.

class="Paragraph">I had to use daylight corrected florrie tubes instead. This meant that at anything other than 25, 50 or 100 I would have flicker problems.

class="Paragraph">Unfortunately the shot was full of working computers all running at different speeds. I was able to adjust these all to the same speed but there was still going to be a flicker problem as I couldn't lock the camera running speed to the monitors.

class="Paragraph">We solved this by setting all the monitors to VGA and 60Hz, this actually measured at 59.94, with my B&S meter, thanks Bill.

class="Paragraph">We then set the shutter to 150 to allow for the monitors at 60 Hz, the 25 fps was safe with the florries at any shutter angle.

class="Paragraph">We checked by running the camera at 29.96 and various speeds around this, no flicker, some small bars, but hey! a 10mm lens and a swooping crane will cover those.

class="Paragraph">This is what I love about CML...

class="Paragraph">Cheers

class="Paragraph">Geoff Boyle...


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