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#1 MITCHELL JUNIOUS

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Posted 15 July 2017 - 12:09 AM

Hello all!

I'm new to cinematography.com and am excited to start participating in different forums. I've posted this question in a couple different forums not knowing which would be the best place.

I am going to be working on a project soon and want to shoot super 16mm. I have been looking at cameras online to buy and have come across some decently priced Aaton XTRs from various countries outside the U.S. My concern is that some sellers have mentioned that they are PAL cameras. Can anyone tell me if this will matter when shooting the film? I have heard mixed opinions about it just referring to frame, rate in which case I can adjust the camera's frame rate. Others have told me that I will constantly have flicker due to electricity in the US. Will I be able to use the camera or should I look for something else?
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#2 Stuart Brereton

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Posted 15 July 2017 - 12:24 AM

PAL and NTSC are video standards, and have nothing to do with film. An XTR should be able to shoot at 25fps for a PAL Transfer, or at 24fps for an NTSC transfer (at 23.98fps).

 

In terms of flicker, it's possible that you might see flicker from discharge light sources if you were shooting at 25fps in the USA. This is because when shooting at 25fps you would usually have a 180 degree shutter which gives you a shutter speed of 1/50 of a second. In a country where the power supply is 60hz, that can cause visible flicker from non continuous lighting like sodium streetlamps. The solution is to shoot at 24fps with a 172.8 degree shutter, which gives you a shutter speed of 1/60 of a second, matching the 60hz power supply, which is what just about everyone does in the US, although TV sometimes shoots at 29.97fps with a 180 degree shutter, which again gives you a 1/60 second shutter speed.

 

It's been a long time since I used an Aaton, but I believe the shutter angle is field-adjustable between 180 and 172.8 degrees

 

 

EDIT. Correction. It's a 144 degree shutter that gives a 1/60 shutter speed at 24fps. A 172.8 degree shutter is used when a 1/50 shutter speed is needed at 24fps.


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#3 Stephen Baldassarre

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Posted 21 July 2017 - 08:22 AM

The solution is to shoot at 24fps with a 172.8 degree shutter, which gives you a shutter speed of 1/60 of a second, matching the 60hz power supply, which is what just about everyone does in the US,

This is a common myth.  The shutter is always running at 24Hz (or 23.976), so reducing the shutter angle simply means it spends more time being closed, reducing open/closed ratio and making flicker worse.  Luckily, most lights don't flicker noticeably, save maybe bad fluorescents.

 

If you want to get into the math of it, let's assume you're using a lamp that puts out no light at all (virtually none do this but...) at minimum voltage and 100% output at maximum voltage.  That means it will be full-brightness 120x per second (peak AND trough give 100% output).  At 180 degrees and 24fps, the shutter will be open for an average of 2.5 peaks (flashes), closed for 2.5.  I say on average because if you're shooting for television, it's actually 23.976fps while the power runs at 60Hz.  The slight difference means sometimes the shutter will be open for 3 peaks.  Sometimes it only catches two peaks.  That equates to a 1/2 stop max variation over several minutes.  By going to 172.8 degrees, it's open 2.4 peaks on average, closed for 2.6.  There will still be times where the camera sees three peaks but has greater likelihood of seeing two.  However, the wider the shutter angle, the longer the exposure (motion blur applies to light too).  A 360 degree shutter will always get 5 peaks while a 288 degree shutter will get 4-5 peaks, which is 1/3rd stop max variation stop over several minutes.

 

In reality, the difference in flicker between 180 and 172.8 is almost nonexistent because even fluorescent lights only dim by a small percentage between peak and trough, assuming the ballasts are decent.  The only time I know of film productions running at 29.97fps are where there's a lot of practical CRT TVs, like Max Headroom or The Wonder Years (3-perf 35mm and 16mm respectively).  In countries using 50Hz power, flicker is worse because the lamps have more time to dim between peaks, so it's a good idea to only use 25fps if you aren't using flicker-free fixtures.


Edited by Stephen Baldassarre, 21 July 2017 - 08:35 AM.

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#4 Robin R Probyn

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Posted 21 July 2017 - 08:53 AM

 Really common myth.. I do this all the time.. changing shutter between 1/50th and 1/60th depending on the Hz...and keeping the same frame rate.. I dont know the in depth maths.. but it works a charm.. no flicker except for weird sodium lights.. or some florrie on the way out.. 

 

If Im shooting 25 and go the US, I change the shutter to 1/60th.. no flicker from the usual suspects at all.. and no viewer is going to know the difference between 1/50th and 1/60th shutter.. and visa versa .. 


Edited by Robin R Probyn, 21 July 2017 - 09:04 AM.

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#5 Stuart Brereton

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Posted 21 July 2017 - 10:01 AM

This is a common myth. 

 

Meaning what? That it's not true? Which part is inaccurate?

 

If you want to see flicker and out of sync pulsing in light sources, try shooting at a sports stadium with a 1/50 shutter in a 60hz country. The solution is a 1/60 shutter. It works, which is why people do it all the time.


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#6 Brian Drysdale

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Posted 21 July 2017 - 10:50 AM

When shooting in the US with my Aaton LTR (which has no shutter adjustment) I ran at 24 fps when using only practical fluorescent lights and didn't have any flicker. However, most of the time we used film lights at 25fps (less audio syncing issues), but if there was any fluorescent lighting somewhere in the background you could see that area gently flickering..


Edited by Brian Drysdale, 21 July 2017 - 10:51 AM.

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#7 Stuart Brereton

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Posted 21 July 2017 - 12:18 PM

Switching to a 1/60 shutter isn't always necessary. Movie lights are flicker free at sync sound speeds, (although HMIs and small tungsten units can flicker at high frame rates). The problem usually arises from industrial light sources like sodium vapor streetlights or old fluorescents without high speed ballasts.

 

I first encountered it when shooting a rodeo in Texas for British television. Our cameras were PAL, and so 25fps 1/50 shutter. When reviewing the material we could see a gentle pulsing in the overhead lighting in the arena, which was some sort of discharge lighting.


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