Yes, the image from a projector can be made smaller or larger using the zoom dial if the projector supports zoom function. You may also make the image smaller by moving the projector physically closer to the screen. You may also make the image larger by placing the image further away from the screen.
If you do move your projector physically too close, or too far away; you may experience the image to be blurry as it will be out of focus based on the spec for the projector lens.
For ideal positioning of your projector based on the projector model, please refer to our easy to use Optoma Projector Distance Calculator tool online. One way to use the Projector distance calculator is to simply know either the screen diagonal size or the screen width and height of the projector screen you purchased (using a tape measure to measure the distance helps with achieving more accurate values). Choose your projector model, installation type and aspect ratio. Then simply enter in the screen values you know in their respective fields and press enter on your keyboard. The calculated result will show up on "Projector screen distance" field which will indicate to you the ideal recommended distance for where the projector should be installed away from your screen. Please note that this projector screen distance is based on the distance from the projector lens to the screen.