Flock It!

Photo of Protostar peel-and-stick flocking paperIf you have a Dobsonian or Newtonian reflector, flocking is a great way to reduce stray light and improve the contrast. What is flocking? It simply means lining or painting the inside of your telescope with something that absorbs light—ideally something that absorbs close to 100% of visible light. Most telescope insides are painted flat black, but that usually doesn’t do a particularly good job of absorbing incident light. If you don’t believe me, look down the inside of your telescope tube in the daylight: is it truly pitch black or just dark gray?

Flocking is particularly helpful in light-polluted environments because there is so much more stray light to eliminate. Think of it this way: if you are in a really, really dark site, flocking doesn’t matter much because there is essentially no stray light. In fact, in really dark skies, you don’t even need a light shroud around a truss-tube telescope—there is just no light to leak into your light path. In contrast, your typical urban or sub-urban environment has plenty of stray light sources: the neighbor’s porch light or bedroom light, the nearby street light, the sky-glow from downtown, and even the light-gray background of the sky itself. If any of this light gets into your eyepiece, it contributes to brightening the background and killing the contrast.

Now flocking is pretty easy and one of the secrets is that you only need to flock relatively small portions of your telescope to get essentially all of the benefits...


A Light Shield for Under $5

Poster board paper light shieldIn urban environments, local lights shining on your telescope can be an even bigger problem than the washed-out skies. Any stray light that finds its way into your telescope tube (or more precisely, into your eyepiece) is a contrast killer, making it even harder to see anything but the brightest objects. While there is little you can do to block general light pollution, you can keep stray light from entering your telescope with a simple tube extension that serves as a light shield.

Poster board paper light shield on 10" DobsonianA tube extension light shield is simply a tube that extends the front of your telescope, making it harder for off-axis light to get into your telescope’s light path. These light shields are particularly effective on Newtonian telescopes because the focuser is too close to the end of the tube on many Newts (especially on many commercial models). Dew shields (such as those commonly used on Cassegrains) also make effective light shields. You can buy dew shields/light shields from various vendors. But you can also make one pretty easily for under $5. All you need is need is some black poster board paper, white glue, and packing tape. It may sound flimsy, but it only needs to stop photons and be stiff enough keep its shape. Here is how I made one for my 10 inch (250mm) Dob …


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