This is topic Formula for throw... screen aspect in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.


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Posted by Dan Chilton (Member # 2288) on 04-18-2004, 04:22 PM:
 
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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Posted by Brad Miller (Member # 2) on 04-18-2004, 04:26 PM:
 
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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Posted by Dan Chilton (Member # 2288) on 04-18-2004, 04:40 PM:
 
Thanks Brad!
 

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Posted by Lindsay Morris (Member # 1430) on 04-19-2004, 03:52 AM:
 
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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Posted by John Pytlak (Member # 331) on 04-19-2004, 10:10 AM:
 
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 ).

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

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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.

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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.

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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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Posted by Scott Norwood (Member # 30) on 04-19-2004, 10:18 AM:
 
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').

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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Posted by John Pytlak (Member # 331) on 04-19-2004, 10:40 AM:
 
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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Posted by Steve Guttag (Member # 268) on 04-19-2004, 12:09 PM:
 
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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Posted by Bill Enos (Member # 440) on 04-19-2004, 04:32 PM:
 
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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Posted by Daryl C. W. O'Shea (Member # 1303) on 04-19-2004, 04:48 PM:
 

quote: Steve

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...I've yet to year shot film referred to as "meterage"

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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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Posted by Martin Brooks (Member # 1269) on 04-20-2004, 07:47 PM:
 
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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Posted by John Pytlak (Member # 331) on 04-21-2004, 08:36 AM:
 
Here are some websites that claim metrification is a foreign conspiracy:

http://www.freedom2measure.org/

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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".

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http://www.metricsucks.com/ (humor)

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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.

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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.

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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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