With life span of population getting longer, more patients need low vision aids. Since modern life involves much more in near work, near magnification for low vision patients is of very importance. There are many methods to determine near magnification power. And there are many low vision devices available. It causes more confusion and misunderstanding. The clinicians interested in low vision are obligated to understand the principles of magnification power. To help low vision patient see the target, the retinal image should be made big enough for visual system to resolve. The size of retinal image is proportionally related to target size and reverse proportionally related to viewing distance. The target size that patient want to see can not be changed. The viewing distance is the only changeable parameter. The shorter the viewing distance, the larger the retinal image. The equivalent viewing distance (EVD) was introduced. EVD is the optical parameter that allows direct comparison between different determining methods and devices. Now the key is how to set a resolution goal for low vision patients. All low vision patients have different goals. Some want to play games. Some want read small prints. Some want to spot read with low speed, and others read for pleasure with high speed. The materials can be rinted in different styles, in different languages, with different colors and different contrast, in addition in different sizes. Reading also involves the discrimination of groups of letters rather than single isolated characters. Thus, word reading may be significantly worse than letter acuity because of the contour interaction effect of adjacent letters (cloudy phenomenon), or may be better because the context effect of meaningful sentences allows the patient to guess some words. To efficiently set a resolution goal for each low vision patient, a comparison method was developed. Ask patients to bring the materials they want to read. Doctor read this material at the distance as far as possible with the speed that patient wants. Record the distance in meter. Find out the comparison ratio of visual acuity (RVA) (measured with word visual acuity charter) between doctor and patient. For example, doctor's visual acuity is 20/20 and patient's 20/100, the RVA will be 5 (20/20 / 20/100). The farthest distance at which doctor can read the material is 0.5 meter. Then EVD will be 0.5 /RVD = 0.1 meter. Now we can prescribe the magnification power for this low vision patient. The following systems provide an EVD of 0.1 meter: 1) a 10 D lens, which focused at 0.1 meter; 2) a 2.5X afocal telescope with a +4 D reading cap to focus for 0.25 meter. This is an image at 0.25 meter magnified 2.5X by the telescope. This is the same as moving the initial object 2.5X closer than 0.25 meter, or 0.25/2.5= 0.1 meter. 3) Video magnifier at 0.5 meter with 5X enlargement: An image enlarged 5X at 0.5 meter is the same as moving the initial object 5X closer than o.5 meter, or .5 meter/5= 0.1 meter.