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Topic: Calculating Image Size Based on Distance & Throw Ratio
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Joined: Dec 29, 2016
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Hi All,

I have a question regarding calculating the image size based on the projector distance and the throw ratio, in the projector BenQ MH530, the specs in metrics are like this:

Throw Dist (m): 1.1 - 9.8
Image Size(cm): 76 - 762
Throw Ratio(D:W): 1.47:1 - 1.62:1

However when using the projector calculator and setting the distance to 1.1(m) then image size is like this:
Width: 71 cm
Height: 40 cm

So the image size in calculator doesn't match the numbers (76 - 762) mentioned in the specs section, am i missing something? What can i do to calculate the image size considering i already have the distance known and using the throw ratio if possible.

Any help is much appreciated.
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Joined: Mar 28, 2005
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The listed image size is generally provided by the manufacturer as a size in which you will get good focus within. So, 76cm to 762cm of DIAGONAL zoom range with sharp focus is what the manufacturer allows for.

If you havea 71cm width, then with the BenQ MH530 you listed, you have an image diagonal of 81cm which would be within focus.

The zoom range is extrmely limited on that projector.

Take the screen width you want, call it 1m. If you have a screen that is 1m wide, then the throw distance (lens to screen) that the projector must be between is 1.47m and 1.62m lens to screen.

http://www.projectorcentral.com/BenQ-MH530-projection-calculator-pro.htm

If you know the screen size you are hoping to achieve, and you know the throw distance you want to use, then you should use the 'Projectors Database' function of the website and put in your information.

So, if you have a 4m lens to screen distance, and want a 304cm diagonal screen (120 inches). Then have a $500 to $3,000 budget range, and want at least 4000 lumens...

http://www.projectorcentral.com/projectors.cfm?g=1&hide=0&st=1&mfg=&p=500&p=3000&w_m=&r=&br=4000&br=10000&ll=<g=&t=&db=&dt=&c=&ar=Wide+%2816%3A9-10%29&dvi=&wr=&pjl_m=&pjw_m=&pjh_m=&td_m=4&is_m=304&i=d&oop=2&sort=pop&sz=15

You can adjust your parameters as necessary.

Or, provide more specifics about your wants and needs here, and I will give you a few potential recommendations.
AV Integrated - Theater, whole house audio, and technology consultation during the build and installation process in the Washington, DC metropolitan area.
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Joined: Dec 29, 2016
Posts: 3
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Thank you so much for the clarification, so i understand that the specs provided by the manufacturer are more like suggested ranges of work and are not necessarily linked mathematically, meaning those numbers do not generate each other exactly through some sort of equation.

The reason i asked this question is that i am really new to this and planning on using the projector mainly for 3D projection mapping purposes for small and medium size events, mainly indoor marketing and wedding related events, and was looking for a projector that would work reasonably in multiple scenarios that varies in distance.

The projector calculator is really helpful but it doesn't help much in giving a perspective of what a certain projector would do in reality in a certain scenario, so i tried to replicate the projector's behavior in 3D software and so far was able to achieve the correct image size based on certain distance, projection angle and aspect ratio, the only problem is that i had to find the angle manually and i found that i could calculate it based on distance and screen width, i can set a fixed distance but i still need the image width (i don't have a specific width), so i thought maybe i can calculate the image width from the projector's specs based on its known min/max distance and min/max throw ratio but i couldn't do so as i specified in my original question.

I am trying this approach in multiple projectors and it really helps in putting them in perspective visually, it is just that it takes long time to simulate each projector because i have to find the angle manually by eye and testing instead of doing it based on calculation which is faster and more accurate.
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Quote (Anas on Dec 29, 2016 9:03 AM):
Thank you so much for the clarification, so i understand that the specs provided by the manufacturer are more like suggested ranges of work and are not necessarily linked mathematically, meaning those numbers do not generate each other exactly through some sort of equation.

Image size is often an exact number. If a manufacturer says it can make an image from 40 to 300 inches in diagonal, then if you want a 320 inch or a 30 inch screen, that's the wrong projector.

The math is entirely in the throw ratio. It is typically expressed as a range, to accommodate for the zoom lens on most projectors. So, 1.3-1.6 throw ratio is a pure math equation. It is the distance from the lens to screen based upon the width of the image. So, for a 10 foot wide screen, you would have the lens 13 to 16 feet from the screen (or anywhere between).

Quote (Anas on Dec 29, 2016 9:03 AM):
The reason i asked this question is that i am really new to this and planning on using the projector mainly for 3D projection mapping purposes for small and medium size events, mainly indoor marketing and wedding related events, and was looking for a projector that would work reasonably in multiple scenarios that varies in distance.

You need to determine then, what screen size you want to work with and at what distances you want to work with. A projector with greater zoom range, like some of the Epson models may be ideal as they have more flexibility in placement. A projector with a zoom lens that offers more than 2x zoom (rare) will give you more flexibility. So, the Epson 5030 may be a better choice, but you won't have a ton of brightness, and you will still need to determine placement carefully.

Quote (Anas on Dec 29, 2016 9:03 AM):
The projector calculator is really helpful but it doesn't help much in giving a perspective of what a certain projector would do in reality in a certain scenario, so i tried to replicate the projector's behavior in 3D software and so far was able to achieve the correct image size based on certain distance, projection angle and aspect ratio, the only problem is that i had to find the angle manually and i found that i could calculate it based on distance and screen width, i can set a fixed distance but i still need the image width (i don't have a specific width), so i thought maybe i can calculate the image width from the projector's specs based on its known min/max distance and min/max throw ratio but i couldn't do so as i specified in my original question.

If you know the distance the projector will be from the object, then the calculator will show you the image size exactly.

For example:
http://www.projectorcentral.com/Epson-PowerLite_Home_Cinema_5030UB-projection-calculator-pro.htm

If you set the Throw Distance to 500 cm, you can click the radio button that says "DIAGONAL RANGE" and you will see that you will get an image diagonal between 200 cm and 428 cm from 500 cm throw.

Quote (Anas on Dec 29, 2016 9:03 AM):
I am trying this approach in multiple projectors and it really helps in putting them in perspective visually, it is just that it takes long time to simulate each projector because i have to find the angle manually by eye and testing instead of doing it based on calculation which is faster and more accurate.

The problem I'm hearing in this is that you don't seem to know your throw distance or image size. Since these are the actual items which matter the most you seem to be guessing at things which really is impractical.

You need to know the image size you want to create. You also need to know the throw distance you would like to have. If you are mapping onto something, you need to know the depth of what you will be mapping onto. Depth of field will be limited on the focus of these projectors, so off-plane images will be more and more out of focus as you move from the center of focus.

I would typically try to work with the projector as far from the object as possible, but depending on the size I want to work with, I would be going for as much brightness as possible.

Perhaps something more like the Epson 1440 which doesn't have the zoom range of the 5030, but has far more real world brightness to work with.

At this point though, you don't necessarily need angles, you need sizes and distances and real numbers to work with. You also need to know that as the projector gets closer, and you zoom out, you will have less and less depth of field to work with and will have a shallower plane to work within.

3D mapping is best achieved with longer throw lenses if there is greater depth to what is projected upon.
AV Integrated - Theater, whole house audio, and technology consultation during the build and installation process in the Washington, DC metropolitan area.
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Joined: Dec 29, 2016
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Thank you so much for your thorough explanation, and you are correct, i really don't have specific distance/image size, i was trying to compare multiple projectors that has 3000 lumens and above with 1080 resolution and see which one has the largest image size, i will try to find specific numbers that would help find the right projector.
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