Jump to content


Photo

Ground glass markings wrong = the lab had to zoom 10%


  • Please log in to reply
15 replies to this topic

#1 Hans Engstrom

Hans Engstrom
  • Basic Members
  • PipPipPip
  • 195 posts
  • 1st Assistant Camera
  • Sweden

Posted 21 February 2008 - 11:45 AM

Did some tests on a SR3 yesterday and today the lab called me and said that they had to zoom in 10% on the negative for the framingchart (1.78), throwing away negative on the sides. They also mentioned that some previous productions using the same camera kit experienced the same problem. The thing is that I was at the lab yesterday and viewed some of the footage, registration test and so on and they didn´t say anything about the framing chart. I thought everything was ok so now I´m 1000km away from the rental company as shooting starts monday. I do have a backup camera and will hopefully get the result on the framing chart for that camera tomorrow. Is the problem as simple that the groundglass markings are wrong or could there be a more serious problem? I have no access to the cameras right now but later this weekend I will try switching groundglass to see if the "framing changes".
  • 0

#2 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19769 posts
  • Cinematographer
  • Los Angeles

Posted 21 February 2008 - 12:35 PM

I suspect the problem is not that the groundglass is "wrong" but someone is misunderstanding what the markings represent.

If the 1.78 markings are for composing for 16x9 broadcast... then they would be 10% inside the negative, to compensate for overscan on monitors -- in order words, the markings are showing you the 16x9 "TV safe" area.

Which is fine, because you probably should be composing within that safe area -- but any scanning and transfers should be using the full negative width, not cropping to match your 16x9 framelines because then the 10% cutoff for some monitors will be inside the area that you've already cropped by 10%.

In other words, either you should have shot a framing chart with a larger 16x9 area that extended to the sides of the negative, with smaller corner marks to show the 10% 16x9 TV safe area (and even though you compose for the inside 16x9 area, you should protect for the larger 16x9 area) or they should just ignore your framing chart and transfer as much of the Super-16 negative as fits in 16x9.

And you should check to see if the groundglass really is showing 16x9 TV broadcast area or the slightly larger 1.78 within 1.68 full aperture.

Remember that the Super-16 negative is 1.68 : 1, so some cropping top & bottom is necessary if you want a full-frame 16x9 transfer.

Truth is that I've always found most Super-16 groundglass markings to be a confusing mix of boxes and corner marks and shaded areas, etc. It's hard to tell what is outside the negative, what is full aperture, and what is TV, other than to assume that the smallest boxes are for TV.
  • 0

#3 John Sprung

John Sprung
  • Sustaining Members
  • 4635 posts
  • Other

Posted 21 February 2008 - 02:12 PM

Actually there are four possible rectangles here.

The biggest is the camera aperture.

"TV Transmitted" is the region that the telecine is supposed to scan. It's usually about 0.008" - 0.010" inside the camera aperture on each edge in the limiting direction, with the other being whatever it has to be to make the desired aspect ratio.

"Safe Action" is 5% smaller than TV Trans, and "Safe Title" is 10% smaller than TV Trans. These are relics of 1950's voltage regulation problems with CRT's. May we all live to see them disappear.

When you shoot a framing chart, be sure it says on it which rectangle(s) you mean it to represent, and which camera body it's from. Charts are an excellent idea, because they zero out a lot of errors and show the telecine colorist the same frame lines you see in the finder. But they can be a two edged sword. A sloppy chart, say one that's tilted in frame, will take some guesswork to set up to. If the top is narrower than the bottom, the colorist will split the difference, and probably not split it exactly the same way for each day's dailies. You should shoot a chart on each body, and shoot a new one if you ever R&R the ground glass.

One of the top TV commercial DP's has a special ground glass that makes his operators compose for a much smaller region on the neg than TV Safe Action. After the spot is cut together, he goes back to telecine, and makes a new transfer of the whole thing, using the extra image to tweak his compositions, much like a still photographer working in a darkroom. You can do interesting things when you have more dollars per frame than even the biggest tentpole features....



-- J.S.
  • 0

#4 Hans Engstrom

Hans Engstrom
  • Basic Members
  • PipPipPip
  • 195 posts
  • 1st Assistant Camera
  • Sweden

Posted 21 February 2008 - 05:50 PM

Thanks for the replies! This particular groundglass only have one rectangle marked 1.78 and the area outside is shaded thats why I think it´s strange. I taped up the lines on a wall and marked the corners with arrows. The lines on the groundglass matched the taped lines to 99% and the corners to 100%. I had the center of the lens (40mm) positioned in the middle of the rectangle to avoid a skewed perspective. I will make some calls tomorrow and see if I can get hold of another groundglass as I know the one in the 2nd camera have the same type of markings (it will be interesting to hear from the lab tomorrow on that one). I got this job in the last minute so I have been working day and night this week including a 1000km drive to get everything together so you can imagine how I felt when I got the call today.
  • 0

#5 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19769 posts
  • Cinematographer
  • Los Angeles

Posted 21 February 2008 - 06:36 PM

Look at the original negative of the framing chart with your own eyes and see how much inside the negative it is. Of course, if the telecine folks aren't lying, then somehow it may be an odd groundglass. I'd compare it to another groundglass.
  • 0

#6 Chris Keth

Chris Keth
  • Sustaining Members
  • 4427 posts
  • 1st Assistant Camera
  • Los Angeles

Posted 21 February 2008 - 09:36 PM

That sounds an awful lot like it's a "1.78 HDTV transmitted area" glass and they are zooming in on the transmitted area.

Does your glass look like the one on page 87 or 88 of the Arri format guide?

Edited by Chris Keth, 21 February 2008 - 09:36 PM.

  • 0

#7 Phil Savoie

Phil Savoie
  • Sustaining Members
  • 94 posts
  • Cinematographer
  • Montana / Wales

Posted 21 February 2008 - 11:54 PM

Great post about how key it is to be accurate with the framing chart John. Like you I shoot one for each camera body, clearly labeling them with the camera info and even placing arrows on the frame line I'd like the telecine Op to crop to. I wonder are you and David shooting the ground glass? By that I mean I shoot it's image not just a framing chart. This way I give the telecine Op a framing chart that doubles as a ground-glass chart for me to insure the Op lines up where I want him to. I set the camera up about 7 feet from a wall, with an 85mm or zoom and shine a Surefire directly in the viewfinder so that it projects the GG image on the wall. Next we tape up a blank piece of white paper and with a sharpie we trace the GG makings, and add the camera info and Telecine line-up with clear labels and arrows. Then we shoot the chart as well as grey cards/scale, color chips and slate the can. I do this with the first roll of every new shoot or lab run or with any new camera. Because I often shoot 3 perf and I'm usually out on location shooting when the first batch goes to the lab this Telecine leader has worked a treat.
  • 0

#8 Chris Keth

Chris Keth
  • Sustaining Members
  • 4427 posts
  • 1st Assistant Camera
  • Los Angeles

Posted 22 February 2008 - 12:35 AM

I set the camera up about 7 feet from a wall, with an 85mm or zoom and shine a Surefire directly in the viewfinder so that it projects the GG image on the wall. Next we tape up a blank piece of white paper and with a sharpie we trace the GG makings, and add the camera info and Telecine line-up with clear labels and arrows.


I'm glad to hear that someone else does it that way. I started doing it and get strange looks when I do it sometimes, but it works like a charm.
  • 0

#9 John Sprung

John Sprung
  • Sustaining Members
  • 4635 posts
  • Other

Posted 22 February 2008 - 01:13 PM

I set the camera up about 7 feet from a wall, with an 85mm or zoom and shine a Surefire directly in the viewfinder so that it projects the GG image on the wall. Next we tape up a blank piece of white paper and with a sharpie we trace the GG makings, and add the camera info and Telecine line-up with clear labels and arrows.

Our guys usually just set up a Panavision chart on a C-stand and line up on it using a zoom lens. Your method is better.




-- J.S.
  • 0

#10 Chris Walters

Chris Walters
  • Basic Members
  • PipPip
  • 82 posts
  • Cinematographer
  • Los Angeles

Posted 22 February 2008 - 08:02 PM

Our guys usually just set up a Panavision chart on a C-stand and line up on it using a zoom lens. Your method is better.




-- J.S.

Maybe this is the cheap and dirty way to do it, but when there is down time or a huge lighting set up, I have just locked off the camera and made tape marks on a wall or on foam core/bead board and run off a few frames.. thats how I've see it done and how i've been doing since.


Chris Walters
  • 0

#11 Chris Keth

Chris Keth
  • Sustaining Members
  • 4427 posts
  • 1st Assistant Camera
  • Los Angeles

Posted 22 February 2008 - 09:05 PM

Maybe this is the cheap and dirty way to do it, but when there is down time or a huge lighting set up, I have just locked off the camera and made tape marks on a wall or on foam core/bead board and run off a few frames.. thats how I've see it done and how i've been doing since.


Chris Walters


That certainly works but you have to be very sure that the chart is parallel to the film surface to get really accurate marks. The beauty of projecting the groundglass through the eyepiece is that you don't have to worry about how straight or lined-up you are. It all looks square from the camera's perspective. I actually think it's faster than lining up a drawn chart properly anyway.
  • 0

#12 Hans Engstrom

Hans Engstrom
  • Basic Members
  • PipPipPip
  • 195 posts
  • 1st Assistant Camera
  • Sweden

Posted 24 February 2008 - 04:28 AM

After having access to the equipment again I have identified the groundglass (Thanks Chris for the link). I (and the productions before me that had the same "problem") assumed that the area that´s not shaded is the full aperature and that the lines represesents 1.78 transmitted but I was wrong, the non shaded area is the 1.78 transmitted and the lines represents the TV-safe area. I have the one on page 87 and thought I had the one on 88. Thanks all! Of to location now.
  • 0

#13 Chris Keth

Chris Keth
  • Sustaining Members
  • 4427 posts
  • 1st Assistant Camera
  • Los Angeles

Posted 24 February 2008 - 11:49 PM

After having access to the equipment again I have identified the groundglass (Thanks Chris for the link). I (and the productions before me that had the same "problem") assumed that the area that´s not shaded is the full aperature and that the lines represesents 1.78 transmitted but I was wrong, the non shaded area is the 1.78 transmitted and the lines represents the TV-safe area. I have the one on page 87 and thought I had the one on 88. Thanks all! Of to location now.


Glad to hear it's all sorted out. Another mistake you'll never make again. :lol:
  • 0

#14 Hans Engstrom

Hans Engstrom
  • Basic Members
  • PipPipPip
  • 195 posts
  • 1st Assistant Camera
  • Sweden

Posted 01 March 2008 - 01:21 AM

Glad to hear it's all sorted out. Another mistake you'll never make again. :lol:


That´s for sure! I´m back now after the first week of shooting and everything is ok. The temperature has been as low as -20 celsius so after working 10-12 hours days outside it feels good to be back home.
  • 0

#15 Chris Clarke

Chris Clarke
  • Basic Members
  • PipPip
  • 71 posts
  • Cinematographer

Posted 01 March 2008 - 07:40 AM

A focus puller showed me a trick a few years ago with an SR3. Remove the magazine, shine a torch through the gate at the same time as through the eyepiece. Now phase the camera and you'll project your ground glass markings as well as the full aperture (flickering alternately) onto a wall. Makes it very easy to compare what you are actually shooting and how much safe area you've really got.
  • 0

#16 Chris Keth

Chris Keth
  • Sustaining Members
  • 4427 posts
  • 1st Assistant Camera
  • Los Angeles

Posted 01 March 2008 - 02:05 PM

A focus puller showed me a trick a few years ago with an SR3. Remove the magazine, shine a torch through the gate at the same time as through the eyepiece. Now phase the camera and you'll project your ground glass markings as well as the full aperture (flickering alternately) onto a wall. Makes it very easy to compare what you are actually shooting and how much safe area you've really got.


There's one problem there. The light coming through the gate could VERY easily be not perfectly straight on. In fact, it would be difficult to get it right. That would, if I'm thinking about it right, make the full negative area not line up with the groundglass markings.

Perhaps he meant to thread some leader or clear film into the gate and do it? That would make a sort of second groundglass to be projected onto the wall. It would make the direction the light is coming from not matter.
  • 0


Abel Cine

Broadcast Solutions Inc

The Slider

Visual Products

Tai Audio

Ritter Battery

FJS International, LLC

Aerial Filmworks

Metropolis Post

Glidecam

Willys Widgets

rebotnix Technologies

Rig Wheels Passport

Gamma Ray Digital Inc

CineLab

Technodolly

Paralinx LLC

CineTape

Media Blackout - Custom Cables and AKS

Wooden Camera

Opal

FJS International, LLC

Ritter Battery

CineLab

Aerial Filmworks

Glidecam

Technodolly

Visual Products

CineTape

Tai Audio

Willys Widgets

Gamma Ray Digital Inc

Broadcast Solutions Inc

Rig Wheels Passport

The Slider

Media Blackout - Custom Cables and AKS

Metropolis Post

Paralinx LLC

Wooden Camera

rebotnix Technologies

Abel Cine

Opal