# Thread: How Can I Calculate Lens Needed for Projection

1. Hello,

I have an image that I want to project. The lens needs to be situated a foot away from the image and I want the image to be projected clearly on a wall about 10 ft. away. How can I calculate what type of lens or combination of lenses I need?

I wasn't able to attach an image of a diagram, but I'll try again later.

Thank you

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4. Originally Posted by ArtScience
Hello,

I have an image that I want to project. The lens needs to be situated a foot away from the image and I want the image to be projected clearly on a wall about 10 ft. away. How can I calculate what type of lens or combination of lenses I need?

I wasn't able to attach an image of a diagram, but I'll try again later.

Thank you
It all depends on how big you want the image.

https://www.boundless.com/physics/textbooks/boundless-physics-textbook/geometric-optics-24/lenses-170/the-lensmaker-s-equation-615-4333/

n in this case is known. And you can determine f depending on the material and the 3 meters of distance and 30cm.

R1 is dependent on the distance of the object from the lens, which needs to be calculated. Use the 30 cm you know for this.

R2 will help you make a certain magnification sharp at a particular distance. You will also need to calculate this one.

You could make a lens assuming R1 = R2.. You would need to rewrite the formula and get something like this.

This is the formula when using a lens.

So to calculate the focal point of a lens. 1/30 + 1/300 = 1/27 ... Focal point would be at 27 cm. You would have a 10 x size increase of your image.

If you want a different size image, you would need to play with the more difficult formula above. One that i have never used myself before..
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