Please excuse my yelling on the forum. I am trying to place emphasis in certain areas and I can't figure out how to underline nor use italics. First let me state the following: THE BEST TELESCOPE IS THE ONE THAT GETS USED. A telescope may have superior optics, light gathering, image and everything else, but if it is nothing more than a museum piece, or a coat hangar, it is useless. You should make telescopes that you feel like getting out at a moments notice and using. Now, in answer to your question, there are reasons for making telescopes with different focal lengths. Here are some of them: 1. Portability. Generally, a shorter focal ratio telescope is a more portable telescope. Like everything else, here is one of the points that you need to weigh against others. Folding an optical path will introduce optical errors as easily as making a short focal ratio telescope. See my opening comment. 2. Image quality. Generally, a longer focal ratio will yield a better AND more pleasing image. There will not be as many optical errors in it, and it is easier to fabricate. 3. Photography. As discussed before, a short focal ratio will give you a shorter exposure time FOR EXTENDED OBJECTS. 4. Optical Design. Some optical designs require longer focal ratios. For example, a doublet refractor made with standard optical glass needs to have a long focal ratio to reduce secondary color. (The blue haze around an image) Folded designs many times are long focus because the image plane and eyepiece are a long ways away from the secondary. This requires the secondary to also be curved. 5. Image Size. Many observing requirements dictate a large image size. This forces a long focal length. Solar telescopes come to mind here. One of the most pleasing solar telescopes I have seen consists of nothing more than a 4” f150 lens. This gives an image size of 5-1/4”. The advantage is that there is never a concentration of the sun’s energy, and everything runs very cool. 6. Special Requirements. Some optical devices, such as h-alpha and other interference filters, will not accept large light cones. In this case, a long focal ratio is required for the filter to work properly. If the light cone is too steep (too large of an angle) the filter will not have the narrow bandpass needed to see only one wavelength. 7. Appearance. Some people just like the looks of a long refractor. It looks more like what people have seen all their lives, and has an “antique” look to it. A telescope sticking way up in the air will attract a bunch of attention at a public star party. Well, there is a long answer to your question. It really depends on what you are going to do with the scope. Some applications dictate long focal ratios and some need short ones. Brent __________________________________________________ Do you Yahoo!? Yahoo! Tax Center - forms, calculators, tips, more http://taxes.yahoo.com/