Film-Tech Forum ARCHIVE: Checking Aspect Ratios By Eye

This is topic Checking Aspect Ratios By Eye in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=001289

Posted by John Pytlak (Member # 331) on 08-11-2000, 02:39 PM:

An easy way of determining the aspect ratio being used in a theatre (when checking up on the competition) is probably right in your wallet or purse (at least if you live in the USA)!

A Federal Reserve Note (paper money in the USA) has an aspect ratio which is very close to the 2.39:1 "scope" aspect ratio specified by standard SMPTE 195.

A regular 2 x 3.5 inch US business card has an aspect ratio of 1.75:1, just slightly less wide than the 1.85:1 ratio specified in SMPTE 195.

So as you sit waiting for the movie to start, bored by the screen ads, pull out a dollar bill or a business card to check the aspect ratio outlined by the screen masking.

BTW, a good way to estimate the width of the screen is to count ceiling tiles near the screen. In the US, many tiles are 2 x 4 feet in size, so you can quickly calculate the width of the screen by counting tiles. I've also learned to pace out the width of a screen, knowing that my "standard" pace is 3 feet long.

Let's just say that I've gotten some strange looks from other members of the audience, as I hold up dollar bills, and pace off the screen width.

For those who need to know, the viewing distance specified in SMPTE 196M is 3 screen heights, with an allowed range of 2 to 4 screen heights. I prefer to sit at 2 screen heights (e.g., 40 feet from a 20 x 48 foot screen).

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

Posted by Evans A Criswell (Member # 381) on 08-11-2000, 03:20 PM:

John,

I find that the "Movie Facts" brochures that many theatres have in the lobby for the taking, are a good way to check a scope screen for the correct aspect ratio. It's an 8.5 by 11 paper folded in thirds to make a 3.67 by 8.5, which is 2.31:1 . I often pick one of these up before entering the auditorium if I am often suspicious of the particular theatre's screen aspect ratios. If the aspect ratio is less wide than the brochure, I align the left edge of the brochure with the screen's left edge and make a small rip where the right of the screen ends in relation to the brochure. I then measure to the rip later to determine the aspect ratio. One time, I found that the aspect ratio of a flat film in one auditorium was 2.07:1 .

I actually made an aspect ratio card last year.

The following quotes are from my "What to Look for in Theatres" document:

"An aspect ratio card is easy to make:

1. Get a rectangular piece of thin cardboard or stiff paper that is at least 2.39 times as wide as it is high. A piece that is 3 to 5 inches in height will work well.
2. Measure the height of the rectangle(preferably with a ruler with millimeters, trying to be accurate to the tenth of a millimeter, which is overkill).
3. Multiply the height measurement by 2.39 and trim the card to this width.
4. Multiply the height measurement by 1.85, and measure that distance out from the left edge of the card and draw a vertical line there, and make a fold there.
5. Now you have a card which is 2.39:1 when unfolded and 1.85:1 when folded.
6. As a "deluxe feature", you may wish to measure out 2.00 times the card height and draw a vertical line there, and if you really get carried away with this, make lines for all of the tenths, such as 1.60, 1.70, 1.80, 1.90, 2.00, 2.10, 2.20, and 2.30. Label them if you do this. Make the 2.00:1 line heavier if you make a lot of lines, since some theatres have 2.00:1 screens, and doing so will help nab them."

"If people look at you funny or ask you what you're doing, use this opportunity to educate them on the difference in the "flat" and "scope" release print formats. If they still think you're weird, well, after the movie, you'll probably never see them again, anyway, so who cares? If you have read this far into this document, you're pretty weird anyway, and are probably used to dealing with strange reactions."

(end of document quotes)

That document is at http://home.hiwaay.net/~criswell/theatre/static_subpages/things_to_look_for /things_to_look_for.html .

I've been using screen tiles to measure screens. I have found that to get accurate measurements, it is best to actually walk from side to side so that you're looking directly at the screen edge without parallax so that you can see exactly where the screen edge would hit on the ceiling if extended vertically. Do this for both and when you get really good, you can consistently know the screen width to within 6 inches if standard 2x4 or 2x2 ceiling tiles are present. Auditorium width and length can be measured using the tiles as well.

Note: It is best to use that "aspect ratio card", movie facts brochure, or dollar bill from as far back in the auditoium as you can get. I have found that using it near the front of the auditorium often gives a slightly different "reading".

Posted by Scott Norwood (Member # 30) on 08-11-2000, 03:31 PM:

Of course, just because the aspect ratio is correct does not mean that the image is cropped properly. The right way to tell is to run a loop of RP-40 test film. This is expensive. A loop of SMPTE "clock-sweep" leader has the 1.85 top and bottom limits marked (they are defined by the top and bottom edges of the smaller circle), which works reasonably well. Scope cropping can often be determined by the cue mark placement, though some labs put the cues farther in than others.

Posted by John Pytlak (Member # 331) on 08-11-2000, 03:37 PM:

You're correct, Scott. The dollar bill and business card method is simply a way of verifying aspect ratio when you're sitting in the audience, and you forgot to bring along your copy of SMPTE 35-PA (RP40) or Evans' aspect ratio card.

I think people would really notice me if I demanded the theatre show my roll of 35-PA before the movie. I never leave home without it!

Posted by John Gordon (Member # 523) on 08-11-2000, 05:38 PM:

John P.,
I too carry a piece of RP 40, not a roll, just four frames. We all must be weird. I also made an aspect ratio card out of clear flexible plastic. I drew lines on it for 1.37, 1.66, 1.85, 2:1, and 2.40. It works pretty good for a close guestimate as to if the masking is set correctly at least. As mentioned, an image can still be wrong even if it has the correct mathimatical size of say 1.85 because of cropping or over sizing.

Posted by Evans A Criswell (Member # 381) on 08-11-2000, 11:08 PM:

John P. : talking about people looking at you funny when "measuring the screen with a dollar bill", one time I was at the Regal River Oaks Cinema 8 in Decatur and after the show, during the credits, after everyone else in the auditorium left, I walked up the right aisle to the front, aligned myself directly in front of the right edge of the screen, looked up, then walked across the front of the auditorium to the left side and did the same. On my way up the left aisle toward the back auditorium's entrance, I saw two shadows back there. Two staff members were watching me and were puzzled over what I was doing. They finally asked me, "Did you drop something?" to which I replied, "No, I was measuring the screen." Then they looked even more puzzled. It was truly a Kodak moment.

Posted by John Walsh (Member # 168) on 08-11-2000, 11:35 PM:

I think it might be useful to memorize how certain scenes look in THX, DTS, etc snipes and compare them to your "test" theater. Won't work for every case, but could be another tool in your mental tool box.

When I was first learning projection, I helped a tech set up the projector, screen and masking. This tech had ordered 5 lenses to try and see which one fit the best. That's a bad sign, I know, but I was new and couldn't tell. The best one still cropped the image (left/right) by 10%, but the height was OK. Yet, he goes to the masking guy and tells him to drop the top masking down.

I say; "But the height is OK, why crop it, too?"

He says: "It must be a 2.35 ratio image. That's a SMPTE standard. I always go by SMPTE standards."

I thought; well OK, I guess, but it dosen't seem to make sense...

Posted by Evans A Criswell (Member # 381) on 08-12-2000, 04:04 PM:

>I think it might be useful to memorize how
>certain scenes look in THX, DTS, etc snipes
>and compare them to your "test" theater.
>Won't work for every case, but could be
>another tool in your mental tool box.

Ummm, I think I've found that many scenes look much more sharply focused and less cropped in DTS. I misparsed your sentence above the first time I read it, which made it much more humorous than it was intended to be. That nutty comment was based on the misparsing! From the correct parsing: The old DTS trailer used to use the full height of the screen, and made misframings of flat films obvious, and also showed if excessive vertical cropping was occurring. I often notice where the pictures are cut off in trailers and then check to see if the cutoff points are the same when I see the trailer in another theatre (provided it's the same format (flat/scope)). It's no use noting this in movies, unless I know I'm going to see the movie again in the future. I watch most movies only once, but I see many of the trailers multiple times.

Isn't it possible to just calculate the focal length lens needed for a certain screen width a certain distance away from the projector using standard formulas found in almost any physics book (by plugging in 0.825 inches, the width of the screen, and the distance to the screen)? Are there factors that require any trial and error, even if the exact focal length is calculated precisely?

Posted by Gordon McLeod (Member # 33) on 08-12-2000, 05:40 PM:

Yes it is possible to calculate even the amount of keystoning
Schnieders lens calc program makes it far less time consuming but working it out in advance is what seperates the engineers from the rest. That said with reel short focal length lens projector and screen frame locations become real critacle and a few inchs of contractor error and all your calculations are in the round filing cabinet
I usually try to order my lens well into construction so at least the walls are up more accurately than the drawings are and real world measurements can be made

Posted by John Pytlak (Member # 331) on 08-14-2000, 08:21 AM:

Here is a link to the Schneider Theatre Design Pro software:
http://www.schneideroptics.com/theatre/desprodn.html

IscoOptic also has a "Cinema Lens Selector" download available on their site:
http://www.iscooptic.de/english.html

Or, dig out that physics or optics book, and calculate the needed focal length from the basic lens formulae.

Posted by John Walsh (Member # 168) on 08-14-2000, 10:40 AM:

Oh, yes, Evans, the picture always looks better in DTS!

I was just thinking of "standard" snipes you'd see at any theater.

It's true that you could just use the lens formula to figure it out. But, I was trying to think of ways to measure the cropping without a tape measure (in case you forgot it) or if the manager might not like you measuring (like at the DLP demos at some theaters.)

Many theaters are painting their ceiling tiles black, so you might not be able to see the runners, or a theater might not use regular 2x4 tiles, etc. The 5% max allowed by SMPTE is not very much, and if your measurment is little off on the throw and the width......