DIY Screen Curve Calculator (Aussie Bob) - AVS Forum | Home Theater Discussions And Reviews
DIY Constant Height > DIY Screen Curve Calculator (Aussie Bob)
mtbdudex's Avatar mtbdudex 05:02 AM 02-08-2009
[edit 3-28-2011]
Tony sent me email Fri 3/25 asking his excel file be removed, "Aussie Bob's Omni-CIH", it had 909 views.
I'm not sure what happened, but I am honoring his request.

Prior thread:
Tony gave "ok", I attach it for download.
File is at bottom of this 1st post, after Tony's comments.
Mod - can you make this a sticky thread?


From: Tony D
Sent: Tuesday, February 03, 2009 3:06 AM
To: R, Mike
Subject: Re: fwd to others or you prefer not? RE: Spreadsheet


Nice to hear from you. Distribute away. As long as they have an idea of where it originally came from it saves me a lot of work.

I'd like to see your extensions. Mine were a bit clunky.




From: R, Mike
Sent: Monday, February 02, 2009 10:14 AM
To: 'Tony D'
Subject: fwd to others or you prefer not? RE: Spreadsheet


How are you?

A few guys on AVS forum have recently inquired to your spreadsheet, I've NOT fwd to them because it's not my IP (Intellectual property), are you OK if I privately email them?
Or is there some other reason I should be aware of? I'll respect your wishes.

I used it for my DIY screen and added some calculations to the bottom to help calculate the different distances to the screen for making standing support blocks.
I was going to post that in my Build thread for others usage.

Michael R P.E.

From: Tony D []
Sent: Thursday, January 10, 2008 6:59 PM
To: R, Mike
Subject: Spreadsheet


Herewith the spreadsheet...

For the pincushion and curvature spreadsheet, make sure you select "Home Theatre" (1) from the System Box. Enter "1" for "Home Theater" in cell B25.

If you're familiar with either the SOLVER or the GOAL_SEEK functions of Excel, you can start out with the pincushion and, say, screen height and then work back to the throw distance (or vice versa if you have the throw distance). I've used these functions to verify that the calculations work (and they do seem to).

Dont forget: throw length is from the projector lens, not the anamorphic lens.

The calculator was actually originally written to calculate screen curvature. Pincushion was part of the solution, so I included that formally in the results box.


You'll also notice a multi-colored box adjacent to the results area. It's an experimental formula I'm trying out to calculate anticipated pincushion percentage directly from just the Throw Ratio. So far it's given pretty accurate results, but raising the TR to the power of 1.9-something-something, needs a sophisticated calculator anyway. The alternative formula is simpler, but less accurate, particularly down the low TR end of the scale. Ignore both if you want to, the figure given in the calculator proper is the most accurate


Get-one-free-get-another-one-free Dept.: I've also sent as "Sheet #2" my spreadsheet for calculating the tilt and yaw angles to which you'll need to set your anamorphic lens if the projector is installed off-axis from the screen's centre point.

You'd be amazed the difference getting these angles right can make to screen geometry, especially if your projector is mounted significantly off-centre to the screen. Trying to get these angles correct by trial and error is frustrating. You get one end right and the other end drifts out. You get the tilt right and the yaw goes off-centre. Maddening!

You need a good starting point. The angles calculated by this tilt and yaw angle spreadsheet are just the ticket for this. Hint: you can usually get away with calculating the tilt and then getting the yaw right by eye. Sometimes when projectors are installed substantially off center-screen - left or right by more than a foot - the angles change a little as there's a keystone effect (despite offsettable projector lenses) which stretches the picture horizontally more than you can easily predict. The tilt, however, remains pretty accurate.

Advantages when you get your angles right:

1. Best focus across the screen
2. Minimize Pincushion
3. Maximize image symmetry

... quite important, in my book, and a lot of HT fans suffer from these without realising what they're missing out on by not having the accurate angles set for their lens.


TONY D (aka Aussie Bob),

GetGray's Avatar GetGray 08:33 AM 03-01-2011
Note: I've seen people referred to this thread a few times lately. Note that there is a newer version. I don't have permission to share though, sorry.
mtbdudex's Avatar mtbdudex 10:36 AM 11-02-2012
I've PM'd Tony and got his ok to post, here is the DIY Screen Curve Calculator file again.
Aussie Bob's Omni-CIH 12k .zip file
brwsaw's Avatar brwsaw 11:27 PM 11-01-2013
What do I need to do to open a zip file on an andriod device?
mtbdudex's Avatar mtbdudex 01:46 PM 11-03-2013
Originally Posted by brwsaw View Post

What do I need to do to open a zip file on an andriod device?
Winzip un-archive app to excel compatible reader app. Search in your android store.
Better yet, do it instead on laptop/desktop to really grasp the information.

There are formulas, etc, not sure if those work on your device.
Do you have access to computer?

Via my 32GB iPhone4 using Tapatalk
brwsaw's Avatar brwsaw 05:34 PM 11-03-2013
Will try it at work.
My PC at home is NFG. Somehow I got locked out of my own PC.
armstrr's Avatar armstrr 07:19 PM 01-02-2014
anyone know how to calculate the distance from the chord to the curve at various points along the chord? other than the middle smile.gif

i started to tape some grid paper together to make a 1/10scale drawing...but it will still be a lot of grid paper!
mtbdudex's Avatar mtbdudex 05:23 AM 01-03-2014
Originally Posted by armstrr View Post

anyone know how to calculate the distance from the chord to the curve at various points along the chord? other than the middle smile.gif

i started to tape some grid paper together to make a 1/10scale drawing...but it will still be a lot of grid paper!

It's kinda buried in my build thread,
Download the excel file in that post, the tab "Pincushion & Screen Curvature" I added my trig 101 to the bottom of it:
paper and pencil

input into excel file

Post pictures of your build in your thread!
armstrr's Avatar armstrr 12:55 PM 01-03-2014
I have just sent this as a challenge to some math-foo has been exchanged for the off chance they succumb... Can you help me calculate a few depth measurements along the chord?
mtbdudex's Avatar mtbdudex 01:21 PM 01-03-2014
What? Revoke your DIY card!! eek.gif
Use this, it's on the web, free.
Can calculate area, arc length,chord length, height and perimeter of circular segment by radius and angle.

armstrr's Avatar armstrr 01:32 PM 01-03-2014
This torus all most made me turn it in in 2004!
armstrr's Avatar armstrr 01:39 PM 01-03-2014
How the find the angle! Then I'm set