Using a Camera Camera: a frustrating infernal contraption which captures your soul in a little box <grin>. If you will only use the telescope visually, use Zero for the variable "Additional Height for Camera". If you will be using a camera, enter the amount of additional height for the focal plane above the focal plane used for eyepieces. This is usually about 2 inches for 35 mm Single Lens Reflex cameras. You should also add any height required for an off-axis guider. This is usually three quarters to one inch. This will increase the probability of vignetting the light cone, because a larger conic section will have to fit through the focuser and other parts of the telescope to reach the focal plane. For this reason, a telescope designed for camera use should have the lowest and widest possible focuser. The size of the diagonal mirror should also be taken into account. A larger diagonal may be required to accommodate the 100% zone desired. This will decrease contrast and block more light from the primary mirror. A telescope should be designed for either visual or photographic work if possible, although a dual purpose scope can be built with some compromises. See Illumination Size.