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telescope. When using a camera, however, you should always wear
corrective lenses to ensure the sharpest possible focus. If you have
astigmatism, corrective lenses must be worn at all times.
Weather conditions
You will be amazed at how quickly seeing conditions change, and what
effect they have on observations! The sky may be clear, but seeing can be
so bad that Jupiter or Saturn might look like they are underwater, and even
low magnification views are not in focus. The next night (or the next hour!)
those same planets will look perfectly focused in your highest magnification
eyepiece and all because the seeing conditions improved.
Before you set up your telescope for a night of observing, get in the habit of
taking a few moments to look up and check the conditions:
• Are the skies clear or are there passing clouds? Knowing there are
clouds in the area helps you understand why an object you are gazing
at suddenly disappears.
• Hazy skies, fog, and mist can also make it difficult to focus when
viewing terrestrially. The amount of detail seen under these conditions
is greatly reduced. Also, when photographing under these conditions,
the processed film may come out a little grainier than normal with
lower contrast and underexposed.
• Are the stars twinkling? If so, are they steady overhead, or do they
twinkle from horizon to horizon? Most of the time, stars overhead are
steady, and the twinkling increases as you move towards the horizon
due to the increased atmosphere. If stars are twinkling overhead, you
have “poor seeing”, but if they are steady almost to the horizon, then
grab your scope and get set up, because the seeing is especially
good, and who knows how long it will last!
• Is it windy? A slight breeze can help keep dew at bay, but too much
wind can degrade seeing conditions and make observing
uncomfortable.
• Is it especially humid out? Is dew already forming on surfaces? Dew
is not a deal-breaker unless it gets so heavy that all of your optics are
affected.
Dealing with dew
Here are a few options:
• Dew Shield: These optical tube extensions fit over the front end of
the telescope and delay the ability for dew to form on the optics.
You can buy flexible dew shields that wrap around your telescope’s
outer diameter and will lie flat when not in use or flexible heated
dew shields that will raise the dew point of the surface to keep dew
away. Choose a dew shield that is made to fit your telescope, or
measure the outside diameter of the telescope and buy according to
those dimensions.
• Dew Strips: Dew heaters, or dew strips, are thin strips of a thick
material that have heater elements running along their length. They
wrap around the outermost edge of the telescope tube, stay put
thanks to Velcro, and plug into a hand controller, which allows you to
adjust the amount of heat applied to the surface. Dew Controllers
often are capable of handling more than one heater, so you can
have one for your telescope, one for your finder, or any other number
of accessories. Keep in mind that dew heaters and their controllers
require DC power, so when considering them, think about how they
will be powered.
• Hairdryer: Many people use a hairdryer to blow away the dew. If you
choose this method, keep in mind that you always want to use the
LEAST amount of heat required to do the job. Overheating your
mirror will only cause distortions of your image until the glass returns
to ambient, and then the blow dryer is needed again. This is why
most people use heater strips made for the purpose. They can be set
to provide just enough heat to do the job, and only around the
perimeter of the mirror, limiting the amount of heat distortion they
cause.
Prepare your stuff in advance
Whether you are driving to a dark-sky location or are observing in your
backyard, it makes sense to make sure you collect everything you will need
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