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nylon stock behind the lens & shooting tv monitor


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#1 Valentina Caniglia

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Posted 26 June 2005 - 09:38 PM

Dear all,

I need help. i have two important questions for you.

I will be shooting a music video in 35mm in three weeks.
I would like to use nylon stocking behind the lens to have my highlights glowing.

I would like to know what kind of stock should I use and which color. Some DPs say that the Christian Dior should be the one to use but I am not sure about the color. Does really matter if you are using a black stock, a white or beige one? If it does what the difference to the effect? What about if you are using a different brand?

Also, I would like to know how should I film regular tv monitors in order to see the image clear without noisy lines scrolling. I know that I could use Plasma monitors but if there is no budget to rent those ones, should I change the shutter angle or frame rate on the 35mm? I shot a tv monitor in HD and I had to change the shutter speed on 144 degree. What about in 35mm? Is it just a matter of changing shutter angle (which one?) or renting a motor that sycronise the 35mm camera with the tv monitor?

How it does work?

I will appreciate your help.

Valentina
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#2 Alvin Pingol

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Posted 26 June 2005 - 10:49 PM

>>Does really matter if you are using a black stock, a white or beige one?

Lighter colored nets will lower contrast moreso than dark/black ones, diffusion of highlights will be more apparent.


>>What about if you are using a different brand?

Different halation effect; i.e. irregular "star" pattern will be different from brand to brand, depending on how the nets are woven.


>>What about in 35mm? Is it just a matter of changing shutter angle

Yes, 144 degrees at 24fps = 1/60th. If shooting a PAL television, shooting at 25fps (180 deg. shutter) will work, too.
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#3 Valentina Caniglia

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Posted 27 June 2005 - 04:17 PM

"Yes, 144 degrees at 24fps = 1/60th. If shooting a PAL television, shooting at 25fps (180 deg. shutter) will work, too."

Thank You Alvin for your response. Let me get this staight though. If I am shooting a Tv set in 35mm I have to change the shutter angle in 144 and keep 24fps in order to see the clear images running in tv. I won't have the problem to see noises like running lines ect.

There is not motor that I have to syncronise with the motion picture camera? The reason why I am mention it is because they told me so.

Anyway, Thanks again

Vale
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#4 Valentina Caniglia

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Posted 27 June 2005 - 08:01 PM

Does any of you knows what is the stop compensation for the net behind the camera? Should I open 1/3 of a stop or 2/3?

Thanks

Vale
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#5 Alvin Pingol

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Posted 27 June 2005 - 09:54 PM

>>If I am shooting a Tv set in 35mm I have to change the shutter angle in 144
>>and keep 24fps in order to see the clear images running in tv

Correct

>>I won't have the problem to see noises like running lines ect.

I'm not too clear on what you mean by "running lines," care to explain? If you mean the dark, vertically scrolling bar that you commonly see when cameras are pointed at television sets, then setting your shutter angle to 144 degrees will reduce it to a very small line. Due to the nature of NTSC not being exactly 60Hz (59.94Hz), however, the line will still slowly scroll across the screen. But no worries, it doesn't look bad.

>>There is not motor that I have to syncronise with the motion picture camera?

If you needed to keep the shutter angle at 180 degrees, you would set the camera to run at 29.97fps. Of course, on playback, the filmed material will appear to be slightly slow-motion.
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#6 Valentina Caniglia

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Posted 28 June 2005 - 09:24 PM

Thanks for your response.

If I use the Plasma monitors I can shoot it on 180 shutter and 24fps?

Valentina
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#7 Valentina Caniglia

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Posted 28 June 2005 - 09:31 PM

For running lines yes I meant - the vertical scrolling bar that you commonly see when cameras are pointed at tv sets.-

I can change the shutter angle at 144 and it will be minimal. Do you know any other way to completely not having the vertical scrolling bar and shooting at 180 shutter speed with 24fps?

Thanks

Valentina
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#8 J. Lamar King

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Posted 28 June 2005 - 11:20 PM

For running lines yes I meant - the vertical scrolling bar that you commonly see when cameras are pointed at tv sets.-

<{POST_SNAPBACK}>



Know to me as the NTSC "roll bar" or "scan bar."
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#9 Alvin Pingol

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Posted 29 June 2005 - 11:43 PM

>>Do you know any other way to completely not having the vertical scrolling bar
>>and shooting at 180 shutter speed with 24fps?

Don't do plasma, as they do not output a purely flickerless image (as do LCD monitors). Plasma monitors don't so much flicker as they do quickly pulsate, and I think each color channel pulsates out of phase from the others. This can cause many problems and headaches.

If an LCD monitor is out of the question, use a traditional CRT monitor with a refresh rate of 72Hz (24*3=72). Any multiple of 24 will work, but I don't know of many monitors that allow refresh rates below 60Hz. 96Hz will work too, if your monitor supports it. This way you'll be able to keep a 180 degree shutter at 24fps.
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#10 Valentina Caniglia

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Posted 01 July 2005 - 12:59 PM

The LCD could be an option. Which rate should I set it?

Thanks for your help.

Valentina
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#11 David Mullen ASC

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Posted 01 July 2005 - 06:09 PM

A 144 degree shutter / 24 fps will reduce the SIZE of the roll bar on an NTSC CRT monitor from a thick band to a thin line. It will still roll, looking like a tiny glitch travelling through the frame.

To stop it from rolling, you need a sync box to phase the camera to the monitor, and a camera speed of 23.976 fps, and even then, you'll still see a thin line -- your choices are to have two lines visible, one at the top third and one at the bottom third, or a single line right across the middle. You can't phase out the line completely.

To have NO line at all, you'd need to be shooting at 29.97 fps and use a sync box. You could then use a 180 degree shutter.

Or shoot at 23.976 fps but use a 23.976 fps video playback set-up (special monitor and source deck) with converted tapes. Again, you could then use a 180 degree shutter.

For shooting LCD's, you don't have to do anything special.
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#12 Valentina Caniglia

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Posted 16 July 2005 - 12:25 AM

Hey David,

the director and I were thinking to shoot a monitor at 16fps. What adjustment I have to make for the shutter speed to avoid seeing the scrolling bar? What happen if I shoot 16 fps with 180 degree shutter speed?

Thanks

Vale
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#13 David Mullen ASC

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Posted 16 July 2005 - 01:09 AM

The only way to not get ANY roll bar when shooting an NTSC CRT monitor is:

Shoot at 29.97 fps / 180 degree shutter. Use a film-video sync box to phase the camera to the monitor.

That's it!

Otherwise, shoot an LCD screen and not get a roll bar at most speeds, if not all.

The other method of not getting a roll bar with a CRT monitor is to hire a 24 fps video playback company. They will bring in a special 24 fps monitor (actually 23.976 fps) and converted tapes of the footage you give them on tape. You will need a film-video sync box to phase the camera to the monitor and roll at 23.976 fps. Your shutter can be 180 degrees.

Shooting a regular NTSC CRT monitor at 23.976 fps with a 144 degree shutter and a film-video sync box to phase the camera and monitor will only allow you to get a frozen line instead of a thick roll bar.

At 16 fps, you'd need a shutter angle of 96 degrees to get 1/60th of a second to make the thick roll bar into a thin one, and a film-video sync box to adjust the frame rate until it stopped moving, but you couldn't get rid of it. This is just my calculation -- I have no experience shooting an NTSC monitor at 16 fps.
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#14 Christopher Wedding

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Posted 16 July 2005 - 12:15 PM

Exactly what is the formula you use to determine the shutter angle based on FPS?
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#15 Christopher Wedding

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Posted 16 July 2005 - 12:21 PM

When putting a nylon behind the lens, do you simply stretch the nylon so that it is taut as you mount the lens?
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#16 David Mullen ASC

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Posted 17 July 2005 - 02:34 AM

Well, you want a 1/60th of a second shutter speed (or maybe 1/59.94 to be more exact, I'm not sure if it matters doing that versus adjusting the frame rate for that difference between 30 fps and 29.97 fps that an NTSC monitor runs at.)

If 360/180 X 24 = 48, all of this under a "1" as in "1/48th" for the shutter speed at 24 fps with a 180 degree shutter, then you can figure out that:

360/Shutter Angle x frame rate = 60 (as in 1/60th of a second.)

So if you know the frame rate, then the same formula becomes:

360(frame rate)/60 = Shutter Angle needed to get 1/60th of a second

But just as shooting at 24 fps with a 144 degree shutter angle gets you a 1/60th of a shutter speed, which then reduces the SIZE of the roll bar from a thick band to a thin line, which won't stop rolling until you adjust you speed to 23.976 fps, then shooting a 16 fps with a 96 degree shutter angle, also getting 1/60th of a second, should also only reduce the size of the roll bar from a thick band to a thin one. I think the speed would have to be adjusted to 15.982 fps more or less to stop the line from rolling (I think you must multiply the speed by .00111 and then subtract that from the speed to get the difference that NTSC runs.) Anyway, there's still a line in the image, or maybe two.

I'm just guessing here, having never tried to shoot an NTSC monitor at 16 fps.

Honestly, fake it with an LCD monitor and you'll be a lot happier...
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#17 michael brierley

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Posted 17 July 2005 - 03:17 PM

With regards to the stocking. Christian Dior #10 Denier used to be the favorite stocking of the older (Brit) DP's. My loader and I roll a thin strip of Blue Tak around the back of the lens, and pull it tight, stretched over the back element/glass, and I would check it every time we did a lens change. I think we compensated about 1/3 of a stop for the net.
Very important to keep checking the tautness of the stocking.

mb
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#18 Manu Anand

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Posted 23 July 2005 - 10:38 PM

Maybe this is inappropriate in the 35mm forum and should be in video but since we are talking about netting behind the lens
Found this on the net a while back ...ive never used it but having struggled with nets on video lenses with blue tack etc to keep them taut this seemed like an interesting solution.

http://shop.store.ya...lies/iring.html

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