If you observe under light polluted skies, this accessory can really help to "punch " thru that and give the view you would have with binoculars. They are also very helpful with hunting down those solitary objects that are not around a star or other known bright object.
Some recommendations here:
Be sure to get the widest aperture possible, the more light the better. 50mm is recommended.
And with low Magnification - like binoculars, this will aid in seeing a wider field of view and neighboring objects to the target.
And with Finders you can get two configurations for viewing, either "Straight Thru" or with a Diagonal (right angle view of its eyepiece). You can view more comfortably with a diagonal, and If you are using Charts, then get a Correct Image type diagonal will really make life easy, since a regular diagonal will give you a mirrored image and you will have to keep thinking as to which way to move the scope to go where the chart says to go.
A finder with a Reticle Eyepiece is very helpful too. An illuminated type even more, if you can afford that, since this is usually a very expensive option.
Finally, if you have both, a Telrad (or DOT/Laser) and Finder, then it is:
1. Locate the area in the sky with the Telrad.
2. Move to the Finder to find and center the target.
3. Move to the Focuser to focus the eyepiece.
There is so much to say about this accessory category, that one could write books on the subject. The following is an attempt to note some of the significant factors, but by no means does this cover it all. In addition to this content, do some research on the internet or at your library to know more.
So, your telescope has to have an eyepiece to function, and you need to match what the telescope is good at, to what the eyepiece is good at, and with what you need and like to see.
First, there many designs, brands and types of Eyepieces to choose from and in a very wide range of cost, and with barrel sizes matching that of your scopes focuser:
It is possible to buy an adapter that will let you use a small diameter barrel eyepiece in a larger diameter barrel.
Besides the design and types, all eyepieces are identified by focal length, again in millimeters, not in power (but of course on cheap scopes, all you hear about is power).
Large value in focal length will yield low magnification power (which could a 40mm or 32mm). This size is used not only for locating and centering the object, but is also useful for wide field objects, such as big open star clusters and wide Nebula's or Galaxies, such as the Andromeda Galaxy..
A medium value (say, 24 to 12mm) is fine for most common sized objects, but usually don't cut it for Planets or very tiny objects such Planetary Nebulas.
For those, you will need a very small value in focal length (such as 9 to 3mm).
But again, to select the best eyepiece for your telescope, you need to know what your scope can do and what it is best for viewing at, and you need to see what is left in your wallet, because this option is, well, kind of like another telescope, it has optical lens, to truly bring the object "sighted" in focus.
If you bought a scope new or used, you usually will get an eyepiece or two with the scope, and that will save you some cost. If not, plan to spend some more, because for most, you will need more than one or two eyepieces to be satisfied with your telescope. Over time, you will likely have a collection of eyepieces, to use your scope to see all types of objects, and that would mean several sizes of focal length, such as having a 40, 25, 12, or a 6mm, in your accessories box. Just bear this in mind.
So, how do you determine magnification?
It is your telescope's focal length (in millimeters) divided by eyepiece focal length (in millimeters).
If you don't know your telescopes focal length, then look it up in the manual (it should be there) or on the manufacturers website. It could be in inches, and if you must first convert those units to millimeters (basic math here).
As an example, a typical 8 inch reflector or dobsonian that has a focal ratio of f/6 is 48 inches in focal length, or 1219 mm (approx). For that scope's focal length, a 40mm would then yield 30 magnification power (approx), a 25 mm would yield a 49 magnification power (approx), and a 12mm would yield a bit more than double of that, or 102 magnification power, and so forth. As you can see, most usually select eyepieces that yield a step of say twice the amount of magnification for each eyepiece size step (or reduction) would give you a nice step or tier in magnification to see various objects for your scope.
Now, once you have your initial eyepiece sizes planned out for your scope, then some other factors and options you need to think of:
Do you wear glasses? If so, then look for long “Eye Relief” eyepieces (15mm or more), especially with high magnification eyepieces. This will save on eye-strain, and having to push your eye right into the eyepiece, sometimes to the point of bumping the telescope off the target. The downside, these may take a bit of adjustment to get use too.
If you do any study of eyepieces, you will find there are all kind of "designs", such as Kellners, Orthoscopic, Plossls, Naglers, etc.. If you are just getting started, the Plossl design is the most popular now for starter scopes, but the eye relief varies with the focal length, and is very short with the 12mm or less..
Wide-field eyepieces are becoming more popular and affordable. This can enhance the view, if your telescope works with it. Low cost eyepieces are usually around 40 degrees in their (apparent) field of view (or FOV), mid cost eyepieces are now moving up and providing 50 to 60 degrees, and then it goes beyond that with eyepieces that have cost that are exponential too. For most, 40 to 60 degrees of FOV are just fine. Again, be sure to listen to David Fullers "The Basics of Telescopes" video on the eyepiece's Apparent Field of View (AFOV) and its relationship to the "Telescopic Field of View" (TFOV).
There are Par-Focal types of eye-pieces. Normally, when you change an eyepiece out for another in your focuser, you have to re-adjust the focus. Par-focals are designed so that you don't have to adjust the focus, saving you time, and for some, a bit of nuisance (who get tired of re-focusing). But you will pay more for this feature,
Then there are specialty eyepieces that are made just for specific object study, such as Planetary, in which case many consider one or two eyepieces from TMBs, which are considered to have set standard in this department. If you are "focused" at a specific type of sky object to view or study, then research an eyepiece that fits your field of study.
And when shopping, you will find that manufacturers have "series" of different types of eyepieces. After years of use, some scopes owners prefer to have just one of these series/type (design) eyepieces alone.
To bottom line it, it is recommended to start slow in acquiring and spending on eyepieces. Take your time, as you get to know your telescope, you need to know your eyepieces too. So, get just a few first, say 3 of them, to try them out first.
In addition, it is highly recommended to attend a local star party, before purchasing more eyepieces. There you ask and see what other scope owners are using and take a look thru their eyepieces, and if you know the person, you could ask if he could put his eyepiece in your telescope for you to see what effect that eyepiece will have. Most other amateur astronomers want to share the view and will usually help you out. You don't know till you try and try on different objects. This is something over time you will get the hang of and figure out what works for you.
There are many more aspects that would be of benefit to know here. So, give yourself some time for study on this (other) investment. Remember, this is a hobby where you learn something as you are having fun. More articles and videos with greater depth of discussion can be found everywhere on this subject: from books, to magazines, and all over the internet. In addition to David Fuller's videos, Orion's resource center has both articles and in the videos on the subject; search thru their index. Wikipedia is always there. And from a quick hunt on the web, you can find several amateur astronomers who have done a great job in covering the topic, usually with text and photos: one such page we found is by Robin Wilkey and his Robin's Eyepiece Guide (Page) that is currently on the Swindon (England) Astronomy club page ["well done" Robin].
Another accessory for an accessory. A Barlow can double the magnification of a given, matching size, eyepiece. Sooooo, yes, you can save some money here on the number of eyepieces in your box by having a Barlow (accessory) that will double the magnification of a given eyepiece, and basically eliminating the need for an eyepiece of that "magnification" step.
Most Barlows provide 2 or more times of an increase in magnification (noted as 2X or 3X, typically), and they come in the same barrel sizes as eyepieces.
They increase the length of the eyepiece end beyond the focuser, but there are short barrel Barlow's available now.
They add more lenses in the optical path and thus there maybe some light loss when using a Barlow, but for most scopes this is very miniscule.
Again, shop around and look'n'see first on these. Most scope owners usually end up picking and keeping one of these in their "bag of tricks".
Filters can really help your view of those faint fuzzy objects, such as Nebula objects, especially in light polluted skies.
There are basically just a few categories to know about:
For a very good, broad discussion video on the topic, see another short (astronomy-motivating) video on Filters by Orion Telescopes.
If you like to study the moon, a Lunar filter will really help with viewing when the moon becomes bright, which is usually any day of its phase when it is greater than a crescent shape.
In addition, ASEM member John Duchek has an great explanation on how color filters can be used for enhancing the view of the moon within his page "Color Filter Study 2011". Be sure to take a look at his images there.
Other Recommended Observing Aids
While it is usually recommended to have a pair of this before you get a telescope, some don't have them yet. And why are Binoculars considered an "aid" to a telescope?, because:
Sometimes you just cannot see those wide field objects with a telescope.
The haze or light pollution in the atmosphere is such that it is hard to get your bearings as to where to start to looking.
And if you have a GoTo mount that requires alignment, sometimes that same case with finding the alignment stars.
All in all, most amateur astronomers recommend having pair on hand when viewing with a scope.
And if you haven't shop or study whats out there, well, yes, you need to do some digging on these too. Again, there's lots of resources to find on the topic of Binoculars, such as that on Wikipedia and the Orion Telescopes resource page, that has both an article and short video on the topic.
Red Lighting and Dark Adaptation
Red lights or lamps are a must when using your scope and any other accessory while viewing in the dark, such as charts or books. Using red-light helps with dark adaptation of your eyesight to the night sky, and to keep that way. Something that is really needed to be able to see those faint fuzzies. Orion Telescopes speaks to this point quite well in their article page here.
If you don't own a red-light, most are common at Astronomy stores, but you can make one yourself, by using a simple white flashlight and rubber-banding over a few layers of red clear Saran-wrap over the end of your favorite flash light, or pick up a sheet of Rubylith film from an Art supply store and cut to fit a piece to place within the light bulb cap end.
In addition, if you are at a star party, it is courteous to use a red light when setting up or tearing down, if others are still viewing with their telescopes in the dark.
And when tearing down, some have found that head-lamps (small LED type lamps that have an elastic band and can fit around your head), that include a red-light mode are just great for this, because they keep your hands-free to picking up and transporting your gear. Such lamps can be found at hardware or sports stores.
Collimation and a Collimator
Collimation of a Newtonian reflector, or Dobsonian, telescope is simply the process of making sure your mirrors and focuser are properly aligned. And if they are not aligned, you will start to wonder why the views of objects, under good skies, are just not as good as they should be. Sometimes this is true with a brand new scope that was shipped a long distance, and very common if you transport your reflector around frequently, which can receive lots of "bumps" along the way that can slightly loosen the screws or bolts that hold the mirrors in their proper orientation. This process is explained very well in a video tutorial at Andy Shot Glass website and in a Sky and Telescope website article, and involves adjusting your diagonal mirror and primary to correct alignment to your focuser and to each other.
And when adjusting the primary mirror on a mid-size reflector, usually two people will be needed to properly complete the collimation. If you try this by yourself, you will know, since you cannot reach the adjusting knobs on the back of the primary mirror while looking thru the focuser at the same time. But a LED laser looking eyepiece thing, commonly referred to as a "Collimator", can allow one to collimate the reflector by him or herself in a very short period time. Now there is some technical debate over the accuracy of this tool, especially on large reflectors, but on mid size reflectors, this tool works just fine, and is worth having in your the scope box or bag, along with your other observing tools. A Collimator can be found at most Astronomy supply stores, starting at $50 and going up.
So you live here in Missouri too, eh? Then you will appreciate having some tools to deal with this issue.
Typical types of Dew Fighting Tools are:
Hair-dryer (if you have an AC outlet handy)
Dew Shields - a wrap around - a necessity for refractors or compound scopes, and even Telrads.
Heat Strips (costly) - nice for refractors, finder scopes, or even eyepieces
or all of the above !
See Sky & Telescopes article on Dealing with Dew for photos and more information.
Star Charts and Planispheres
Do you know where to look and what to look for? Well, with a GoTo scope or having a laptop, tablet or smartphone, on hand, yeah, you maybe able to point your scope in the right directions with thse "electronic aids" these days. But, if you don't have any of those devices, or your batteries are shot (oh-no), then good old star charts, books (with charts) and Planisphere's can still be useful, provided you have a red-light handy.
One of the best, nice sized, star charts out there is Sky & Telescope's "Pocket Sky Atlas". See the review of it on CloudyNights Telescope Reviews. This is considered a great resource to have when you are starting, a great back-up, if those electronic devices are just not working.
Remember, if it is paper and you live where the Dew is, then be sure to keep your charts, books, or Planisphere, in a box, bag, or under plastic or vinyl protection.
Planispheres are available in vinyl material, as well, so forget the Dew. The "Night Sky Planisphere" is the most popular, with blue on black, but if your eyes appreciate a darker background, then check out The Miller Planisphere, that is a bit darker with white text on black or blue backgrounds. Both are very affordable, in most stores, and sometimes at hobby stores, and are sometimes made for specific latitudes - so be sure to read the title/description before purchasing.
Maintenance and Protection
Keeps exterior surfaces dry and clean
Especially the optics
Reflector mirrors - may need periodic washing but no more than once a year. Frequent cleaning can affect the life of the mirror's reflective coating. So, be very careful here, do some reading here on this.
For refractors and eyepieces, it is recommended to get a cleaning kit for lenses, but you will hear not everyone agrees with cleaning everything. But if you feel its time, one should use only special wash and rinse. The best solution is to pick up a lens cleaning kit, such as one that is available from ASEM member John Duchek, on his Astronomy Product Page.
Dust Covers and Caps
If your scope and gear was just brought in from under the dew or out in the cold, then be sure to let it all dry out indoors before returning everything to storage in containers or bags.
How to Use your New Telescope
Practice and Patience
A good quote: “The more you look, the more you will see, and the better you will get.
Astronomy is a patient hobby. Don't be in too great a rush. The cosmos will still be there tomorrow.”
Typical 6" reflector
When under good clear skies, the view should yield:
All 110 Messier objects
All of the planets except Pluto.
Saturn's rings are easy.
Moon shadow transits on Jupiter are easy.
Detail on Mars is somewhat harder,
Venus, Mercury, Neptune, and Uranus
Hundreds of named craters on the moon.
When wanting to look at the Sun
Use with a proper filter.
Do not look at the sun without proper filtration!
Be careful here - study up on this and check with those who do it first
Use of Your First Telescope
Start with bright objects
Moon, bright stars and major planets (Jupiter or Saturn)
Use your telescope's lowest power
You should not see any distracting flares or colored halos.
With experience, step up your power (use shorter focal lengths).
Check your new Scope
Keep in mind, perfection is expensive, and that a lot can be seen with less-than-perfect equipment.
Be patient with your new telescope and with yourself.
Practice, like any hobby
Ask for help if you have questions - talk to ASEM or club members
And enjoy the view
If Buying a New Telescope
Read, Study, and Talk to Others
Ask Lots of Questions
Go to a Star Party
Decide How much you can spend
Glass, not plastic, optics is what you want
Local – Creve Coeur Camera has limited stock of low-end Celestron brand telescopes
Do your research on this investment! Go online.
Kick the Tires and Use it!
If concerns, have experienced scope owners check it.
If new, be sure to know warranty and return policy.
Resources to Help You with Your Telescope
Check ASEM and other clubs, and what can they offer you!
Again, continue to read, study, and research the Internet - There is a lots out there
And don't forget about taking your new scope to a Star Party
Again, all of us at ASEM hope this information helps you with your first telescope and the beginning of a life-long and interesting hobby of Astronomy.