Projector Throw - Check for me

[Lara]

I just wanted to check my calculations for this projector setup.

Image Width = Throw Distance/Lens Value
[is this formula correct?]

Throw Distance = 3327.5mm

Projector Lens is:
http://www.wedgwood-group.com/sanyo_lns-w31a_short_zoom_projector_lens.htm
Throw Ratio: 1.3 - 1.8:1

3327.5/1.3 = 2559.62mm

Image width: 2.56m
[Is width measured horizontally or diagonally here?]

Thanks so much

Lara x

[lowRes]

hi!

unfortunately i'm always messing those calculations too..
one way i've used to solve them is using the calculator applet at projectorcentral (http://www.projectorcentral.com) .

hope it helps u!

* )
r_x

[spaceman]

with a throw distance of 33.27 meters your image will be:
18.47*13.87 m with 1.8 ratio to 23.76*17.82 with 1.4 ratio

lenght of picture=distance/throw ratio
hight of picture=lenght*(3/4)

you can do the opposite
distance=lenght of picture*throw ratio

[Lara]

Hmm.. thanks lowres, but I'm adding a lens to the projector so can't use projector central.

Ah right I do understand your calculations now Spaceman wooo hoo

Are we definitely right?? People please check em and lemme know

[syzygy]

spacemans calculations look right, apart from a throw distance of 3327.5mm (laras calculations) is not the same as a throw distance of 33.27 m

since 1m = 1000mm, 3327.5mm is about 3.33m


also, spaceman used 1.4 as the minimum throw ratio for the lens, but lara gave it as 1.3

I get the following results:

maximum projection:

width = 3327.5 / 1.3 = 2559.6mm (2.56m)
height = 2559.6 * 3/4 = 1919.7mm (1.92m)

minimum projection:

width = 3327.5 / 1.8 = 1848.6mm (1.85m)
height = 1848.6 * 3/4 = 1386.45mm (1.39m)

[solly]

Don't forget to take into consideration the angle and keystone effect which could change your calculations dramatically, unless you want to be exactly in front of your screen.
Solo

[syzygy]

good point solly.

Its hard to take keystone into account exactly, but a rule of thumb that I tend to use is to measure the throw distance to the nearest part of the projection when doing keystoned images.

Digital keystoning reduces the projection size at the end with the longer throw distance, usually leaving the other end unaffected. Some do mess with the other end too though, so when using keystoning, its wise to operate in the middle of the zoom range of the lens, to have some leeway for adjustment.

[spaceman]

oops.... :o
(havn't used metric in a while)

how did you get such precise measurement btw?, is that autocad or converted from imperial?

[sleepytom]

keystoning shouldn't make much practical diference to throw distance.
keystone correction should only be used to correct small errors - projectors with interchangable lens systems normaly also have lens shift which can be used to change the H/V position of the image relitive to the projector.

if the mesurements are converted from imperial check if they are in feet and inches or architectural measurements (feet and 10ths of feet!)

its allways best to get into the space and measure it yourself first if possible - also bear in mind that the lens of the projector will be nearer the screen than the rigging point (with small projectors this is not too bad but with bigger ones it can push your image over the edge of the screen)

a V4 can be used to mask / shrink the image if you can't get the right lens!!