improving your telescope

**I have a telescope already. How can I improve it cheaply?**

* If you already have a cheap refracting telescope on a tripod, there are a few ways to improve this setup without spending too much money.
   * **Eyepieces:** First of all, if you have an eyepiece which has the prefix H, SR, or R before the number ("H20" or "SR4" for example), you have some of the worst eyepieces ever made. Three-element Kellner (or "modified achromat") eyepieces are cheap but useful and you can get some decent quality replacements for 10-20 dollars each. Plossls are a step up as they use four-element lenses, and Gold-Line type eyepieces are cheap options for high-power, high field of view eyepieces. Some people spend hundreds of dollars per eyepiece, but this is not necessary. **You can only upgrade eyepieces if your eyepieces have 1.25" barrels.** If they use 0.965" barrels, your telescope may not even be worth spending any more money on--it's a sign of being incredibly cheap, and to do so you'll need a special 0.965-1.25" adapter diagonal.
   * **Choosing Eyepieces**: If you're building up a brand new set of eyepieces, you may want to choose magnifications suitable for your scope. The number written on the barrel of the eyepiece is the focal length in millimeters. A lot of cheap sets sell based on magnification instead of the more relevant aperture size. The formula *Magnification = Focal Length of Telescope / Focal Length of Eyepiece* is useful. The maximum magnification you can reasonably use in a telescope is determined by its aperture. You can get no more than about 50x magnification per inch of aperture. (or about 2x mag per millimeter of aperture). On most telescopes, the focal length and the aperture diameter in millimeters are written on the telescope tube somewhere. If not, you may have to find the manual or look up the model online to find this information. The minimum magnification is given by 3.6x mag per inch of aperture. If you overpower or underpower the scope, you'll get a low quality image. Low power eyepieces are
      * If you can get just one eyepiece replacement: choose an eyepiece which would result in a low or medium magnification.
      * If you can get just two eyepiece replacements: choose a medium-power and a low-power eyepiece.
      * If you can get three: get high, medium, and low powers.
   * **Barlow lenses:** Barlow lenses are used to increase the focal length of the telescope and thus increase the magnification when used with a given eyepiece. They're usually 2x, but cheap sets often include 3x or even 5x barlows--entirely unnecessarily. Very expensive Barlows can be very useful, but the odds are the Barlow you got with your cheap beginner set was included just to get to whatever absurdly high magnification number was written on the box. The Barlows included with cheap sets might as well have the optical quality of a beer bottle. Don't use the Barlow that came with your cheap telescope if you want a good optical quality. An expensive Barlow is a good investment, but this is a guide for *cheap* astronomy.
   * **Diagonal**: A lot of refractor telescopes have a removable diagonal adapter to make the viewing angle more comfortable. These will either use a flat mirror, or an image-erecting set of prisms. In cheap telescopes, this may be such low quality that it's not worth using it. Ideally, the diagonal won't affect the image in any way. So if you remove the diagonal and just place the eyepiece in straight through, and the image looks better, then you might want to either keep the diagonal out, or buy a higher quality replacement.
   * **Tripod**: There's not a whole lot that can be done if the tripod is wobbly or if the mount is unbalanced. But you could try to put counterweights hanging down on the tripod to force the center of mass down, or put counterweights onto the optical tube if it's out of balance.
   * **Is it worth it?** If you have a very cheap telescope, upgrading its components to make it useful might end up being more expensive than just buying a better telescope. If you are working out the budget for these changes and you end up with a price over 100 dollars, getting a 100-200 dollar tabletop Dobsonian with the same money might be a better deal.
* If you already have a decent telescope but want to upgrade it cheaply:
   * Goldline eyepieces are cheap, high-field-of-view, high-magnification eyepieces that many amateur astronomers recommend. Use the magnification formulas above to determine which eyepieces your telescope can use. Goldlines are sold by many different brands, some sold without the characteristic gold bevel. Read [this review on telescopicwatch](https://telescopicwatch.com/goldline-eyepieces/) for more info.
   * Get a Barlow lens for about 50-60 dollars. It will double the magnification of your eyepieces, and assuming there's no overlap, it will double the number of magnifications your eyepiece set has.