When discussing focal ratio it is also necessary to discuss magnification. Contrary to popular belief magnification is the least important factor in purchasing a telescope. The reason is because the more you magnify an object the dimmer and more blurry i t becomes. If you have superb optics on your telescope the greatest useful magnification you will get is about 40-50 times per inch of aperture. But, in reality you probably will get nowhere near that much magnification with a good image because of bad seeing which is a disturbance caused by hot and cold air meeting in the atmosphere that will make your image blur and deform at high power.
Dobsonian mounts are mounts for Newtonian reflectors that are altazimuth in design.
They are extremely stable because they are very low to the ground and they are made of wood. They have bearings made of nylon or teflon which allows it to move in altitu de or azimuth very smoothly. The greatest quality of the Dobsonian mount is that it is very inexpensive, works well and it can even be made easily at home. Standard altazimuth mounts are used mostly on refractors. They work like the Dobsonian mount but they are much less stable.