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Author Topic: Formula for throw... screen aspect
Dan Chilton
Expert Film Handler

Posts: 191
From: Springfield, MO
Registered: Mar 2004


 - posted 04-18-2004 04:22 PM      Profile for Dan Chilton   Author's Homepage   Email Dan Chilton   Send New Private Message       Edit/Delete Post 
Does anyone know if there's a formula for calculating the size of your projection dependent upon the projector's distance from the screen? I realize that the size of the projection would vary, depending on the format of the film (flat, scope, and otherwise), so I'm just looking for a ballpark estimate... formula. Thanks!

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99


 - posted 04-18-2004 04:26 PM      Profile for Brad Miller   Author's Homepage   Email Brad Miller       Edit/Delete Post 
The Lens Calculator program at the bottom of the manuals page is super simple to use and will suit your present need fine.

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Dan Chilton
Expert Film Handler

Posts: 191
From: Springfield, MO
Registered: Mar 2004


 - posted 04-18-2004 04:40 PM      Profile for Dan Chilton   Author's Homepage   Email Dan Chilton   Send New Private Message       Edit/Delete Post 
Thanks Brad!

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Lindsay Morris
Expert Film Handler

Posts: 233
From: Darlington, WA, Australia
Registered: Sep 2002


 - posted 04-19-2004 03:52 AM      Profile for Lindsay Morris   Email Lindsay Morris   Send New Private Message       Edit/Delete Post 
There area couple of formulae that I use from time to time that might be of help if you are not close to the computer and can do a couple of simple maths calcs. A calculator also helps to quickly whack it all out.

Throw = Image width divided by Frame width multiplied by lens focal length.

In USA you seem to prefer inches and footsies so use Feet & decimals of inches to apply to the formula.

EG A Screen width of 14 feet, frame width = 0.825 inches and focal length = 5 inches produces a throw of 84.8 feet.

That basic formula can be shuffled about to give you any other unknown if you know the other 3 variables.

Screen image size = Throw multiplied by frame width, divided by focal length.

Focal length reqd = Throw multiplied by frame width, divided by picture width.

The only exception is when you are sorting out scope or anamorphic sizes as that factor (usually 2) plays merry hell with the WIDTH calcs but has NO effect on HEIGHT calcs. (You can use the height of frame and height of screen in place of width if you so desire).
In the example above the screen size would be 28 feet due to the scope lens spreading the image by a factor of 2 horizontally.... so you have to think about what you are trying to do when it comes to scope images.
There is often small errors of just how much a certain scope lens will spread the image.. some seem to have more spread/squeeze than others even from the same maker at least the ones I have had to deal with have such as B&L,Prominar and even a Moller.. not played about with an Isco as yet. Probably not much of a problem with a single machine but if you are running changeovers you can often see the slight shift on each change.
But if the screen is masked one would never see it but in a DI or an outdoor that is a different story. I ran a Moller and a B&L in the initial setup I started up with and the B&L had more spread than the Moller so I had to have the aperture plate slightly smaller on the machine using the B&L lens. (There can be quite a bit of adjustment to be had by carefully adjusting plate dimensions. Overdoing it can leave you with DTS codes visible on the LHS and editing flashes top and bottom on scope prints if you take the height to far up... as I found out trying to fill the screen totally).

I much prefer to use ALL metric when using the formula as it is SO much easier.
EG Frame width in mm's and focal lengths (as most lens seem to be branded in mm's rather than inches nowadays) and the throw in metres and decimals of that.
To me a throw figure of 33.65m is much easier to fiddle about with than trying to get a decimal measurement of feet and inches... what the hell is 100' 9".... 100.75' but you have to think about it a bit... well at least I do now.
Much rather have metric measurements it all just drops into place so easily.
Lindsay

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000


 - posted 04-19-2004 10:10 AM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
I am all for the US adopting metric units of measurement (International System of Units). Yet I recognize that there are some "die hards" who still cling to "English" units of measurement (including my wife [Roll Eyes] ).

http://lamar.colostate.edu/~hillger/

quote:
The U.S. Metric Association (USMA), Inc., with headquarters in Northridge CA, is a national non-profit organization, founded in 1916. It advocates U.S. conversion to the International System of Units which is known by the abbreviation SI (ess-eye). SI is also called the modern metric system. The process of changing measurement units to the metric system (i.e. SI) is called metric transition or metrication.

This site contains information on the SI metric system and information on the status of metric transition (metrication) in the United States. Information is also available on USMA's accomplishments, activities, and resources, as well as links to non-commercial Websites with additional metric system information.

Conversions between unit systems are a poor way to learn the metric system, and conversion factors can make the metric system look complicated. Therefore we do not support or directly link to any unit conversion utilities. However, conversion utilities are available through some of the non-USMA metric sites in the links section near the bottom of this page.


http://www.pueblo.gsa.gov/cic_text/misc/usmetric/metric.htm

quote:
The United States is now the only industrialized country in the world that does not use the metric system as its predominant system of measurement.

Most Americans think that our involvement with metric measurement is relatively new. In fact, the United States has been increasing its use of metric units for many years, and the pace has accelerated in the past three decades. In the early 1800s, the U.S. Coast and Geodetic Survey (the government's surveying and map-making agency) used meter and kilogram standards brought from France. In 1866, Congress authorized the use of the metric system in this country and supplied each state with a set of standard metric weights and measures.


Link to US NIST metric website:

http://ts.nist.gov/ts/htdocs/200/202/mpo_home.htm

The movie industry is especially bi-polar: e.g., 35mm film projection speed is usually stated as feet per minute.

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Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99


 - posted 04-19-2004 10:18 AM      Profile for Scott Norwood   Author's Homepage   Email Scott Norwood   Send New Private Message       Edit/Delete Post 
I always thought it was odd that film is sold in metric widths (8mm, 16mm, 35mm, 65mm, 70mm) and Imperial lengths (100', 200', 400', 1000', 2000'). [Smile]

One thing that does get annoying is when a theatre upgrades from old lenses (focal lengths measured in inches) to new ones (focal lengths measured in millimeters[res]) and then finds that the image size is slightly off (because the focal length increments are different and exact matches are usually impossible).

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000


 - posted 04-19-2004 10:40 AM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
Actually, 35mm movie film originated when W.K.L. Dickson first ordered film from Kodak. Kodak made a 2-3/4 inch wide film for still cameras. When slit in half, it was 1-3/8 (1.375) inches wide, which is 34.925 mm. The first SMPE Standard in 1917 showed a width of 1.375 inches, not 35mm. I think 35mm became the nominal width when Leica in pre-war Germany adopted motion picture film for its first 35mm still cameras.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999


 - posted 04-19-2004 12:09 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
Heck, even the Metric countries of the world...the refer to the "footage" of the film...I've yet to year shot film referred to as "meterage"

Steve

P.S. I too would advocate the switch to SI units for the USA. Back in college, of my professors speculated that the 1/4-20 screw is what was stopping it all...it was too prevasive as the most popular thread pitch for a fastener. Yet most cars, American included, use metric fasteners now.

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Bill Enos
Film God

Posts: 2081
From: Richmond, Virginia, USA
Registered: Apr 2000


 - posted 04-19-2004 04:32 PM      Profile for Bill Enos   Email Bill Enos   Send New Private Message       Edit/Delete Post 
I just took a look at all the domestically made stuff I've bought in the last few months, including some furniture. All the hex fittings are metric. I think I read recently that even Harley Davidson has gone metric, even on the non V-Rod models. A number of years ago there was a major metrication effort, what happened?

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Daryl C. W. O'Shea
Film God

Posts: 3977
From: Midland Ontario Canada (where Panavision & IMAX lenses come from)
Registered: Jun 2002


 - posted 04-19-2004 04:48 PM      Profile for Daryl C. W. O'Shea   Author's Homepage   Email Daryl C. W. O'Shea   Send New Private Message       Edit/Delete Post 
quote: Steve
...I've yet to year shot film referred to as "meterage"
I've had a studio booking employee ask me "how many metres of the film is damaged" when I called to reject a reel. I just replied, "512 feet, where are you from?"

I too prefer metric when it comes to building things, especially taping threads.

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Martin Brooks
Jedi Master Film Handler

Posts: 900
From: Forest Hills, NY, USA
Registered: May 2002


 - posted 04-20-2004 07:47 PM      Profile for Martin Brooks   Author's Homepage   Email Martin Brooks   Send New Private Message       Edit/Delete Post 
What happened was that we're too stupid to deal with metric units and it became a political issue: that somehow switching to the metric system was akin to letting the UN make decisions for us.

Then schools started backing away from teaching the metric system and instead started teaching only how to do conversions. Then they dropped it completely.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000


 - posted 04-21-2004 08:36 AM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
Here are some websites that claim metrification is a foreign conspiracy: [Roll Eyes]

http://www.freedom2measure.org/

quote:
The imposition of the metric system without recourse to the democratic process is wrong. It is an affront to our basic rights. How we measure is part of our heritage and our way of life. Don't let unelected unaccountable bureaucrats and careless unresponsive legislators sacrifice it under the steamroller of World "harmonization".


http://www.metricsucks.com/ [Wink] [Big Grin] (humor)

quote:
Although the metric system is slowly creeping into US culture, we have stood up to the French more than most other nations. Even though our monetary system is decimal and many stuffy old scientists may prefer the grams and meters, the US luckily retains her independence from the invasive French metric system.
http://www.users.zetnet.co.uk/estatopia/inch.htm

quote:
The world is slowly being forced by governments, civil servants and multi-national industries into adopting the metric measurement system in place of the traditional systems which have been in use for centuries, for millenia in fact. The use of metric units has been legally acceptable in the UK since 1897 and in the USA since 1866 and yet the traditional system prevails in spite of this option. If metric were an improvement on traditional measurements then it would have been universally adopted long ago. The truth is that metric offers no advantages to people in their daily lives and will never be used unless it is forced upon us by criminalising the use of imperial measurement, something which is happening now in the UK and has happened in every other country where metric is used. In fact, the people of other countries have never voluntarily adopted metric, it has always been imposed upon them against their will by politicians and bureaucrats.
http://www.sendbackliberty.us/otherchanges.php

quote:
The metric system is just another example of the French forcing their way of doing things on eveyone else. We think that everyone should go the extra mile and avoid using the metric system. Our allies in the War Against Saddam And Terror, the UK, uses the Pints, Pounds and Ounces, and our enemies, the French, don't. Why should we?

Compulsory metrication is undemocratic. In the USA we are free to do what we like, say what we like, but not measure how we like! Did you ever vote for the metric system? Our American weights and measures are units that we know and use. They are part of our heritage. Metrication will destroy part of our cultural inheritance and also weight us down with a difficult and meaningless system. The metric system is already creeping into the USA right now!


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Alan Haigh
Film Handler

Posts: 45
From: Watford, UK
Registered: Jul 2003


 - posted 04-21-2004 08:48 AM      Profile for Alan Haigh     Send New Private Message       Edit/Delete Post 
They are only measurements - they won't really destroy your culture, you won't let them. The "metric hating" aspect of the UK has been very exaggerated by our "wonderful" tabloid press, who seem to think we are still fighting the second world war. I can still ask for a pound of apples in a shop, and they will give me it. The difference is now that I MUST be able to ask for half a kilo, and their scales must measure kilos. So people from continental Europe aren't confused. To me it is so simple - metric is like counting in tens - you can do all calculations without dividing by 12 or anything, so I prefer it. However an inch (when building) or an ounce (when cooking) is a "sensible" amount of something. One gram of butter is meaningless. So it's sometimes "handy" to work like this. By the way our entire building trade now uses millimetres for measurement. No one has died, and no culture has been lost - they still don't turn up when they say!

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