Author Topic: Did you know of these different types of telescopes? (Thread from a beginner to  (Read 98 times)


  • Active Astronomer
  • ***
  • Posts: 118
  • Activity:
  • Reputation: +0/-0
    • View Profile

this is meant to be a beginner thread from a beginner to a beginner as I am pretty sure that everyone else already knows about these. I thought I would just share with new people what I found on my journey of just picking a telescope good for my own needs (still on-going at the time of writing).

3 main types of telescopes:

1.) Refractors: These are lense-based telescopes. Depending on quality of the telescope these contain anything between 2 and 6. Simple refractors suffer "purple-fringing" surround especially bright subjects (ak chromatic abberations) which are the result of different colors of the light spectrum being bent to different degrees. To fight this symptom, higher quality lenses were developed. Telescopes that have these lenses are called achromatic telescopes. More sophisticated setups contain various concave and convex lenses to focus different colors into one focal point again. These sorts of telescopes are called apochromatic telescopes. Because these telescopes contain many lenses with many surfaces, that each have to be finely crafted, they are the most expensive. Prices increase quickly...and for these telescopes it is not too uncommon to see prices as high as 10K for a moderately sized siystem (5-6").

To get started though, one does not need to pay exorbitant amounts. Here are a few (mostly achromatic) telescopes:

- 102mm Achromatic Refractor: 4" telescope with good wide field of vision. I have seen sale prices as low as $399 for the OTA only.
- 127mm Achromatic Refractor: 5" telescope with better light capture then the model above. Normal prices are around $599.

I have read many good reviews. Good price for quality achieved. Of course, at these prices you are not going to fully eliminate purple-finging, but it should not be very noticeable with these achromats. Bigger sizes are also available, but they, in my opinion start getting unwieldly large. Smaller sizes are going to be cheaper of course, but for those you will be limited to brighter objects (such as planets, and the really brightest and biggest nebulas and DSOs)

2.) Reflectors: These are "mirror-based" telescopes. Instead of lenses, mirrors are used to bundle the light. They are MUCH cheaper because, instead of polishing 4-12 surfaces, one only needs to do a good job on the primary mirror (1 surface). It's common wisdom that in terms of bang for the bug, this is where you will likely find it. I personally have been exploring 5" newtonians on a Go-To mount, and found that basically, the OTA is the same piece of equipment in each of them. Examples below:

- Celestron Skyprodigy 130:
- Celstron 130 SLT: The link to this is actually a review meaning to show that despite the concerns below, people can be happy with these sorts of systems.
- Orion Starseeker IV 130:

People on these forums will quickly point out that there are several issues with these scopes. Despite great optics of the mirror, these scopes come on very undermounted tripods - at least the Skyprodigy and SLT system. I can attest to that as I looked at the tripods for the first 2 models. I have yet to see the Starseeker IV tripod. It appears to be more solid and might be acceptable actually. The other piece I WAS able to confirm though is that the Celestron telescopes mentioned above have a plasticy looking focuser piece.
People on the forum say that these focusers will prevent great accuracy at higher (~200x) magnifications. Again, I have not been able to confirm this for the Orion model.

When I was in 2 different stores, I found it kind of interesting: Newtonians below 6" were made in the cheapest possible way. Most were afflicted by the above type problem. I could not find well-built telescopes below 6". If the community or searcher did find Newtonians of this sort do point it out! What I found instead was that 6" somehow represents the magic boundary for for well-built Newtonians with solid tripods (of course, one buy tripod/mount and ota separately but somehow this is less cost effective). I don't know why that is, but one outstanding example I think is the below:

- Celestron Advanced VX 6" Newtonian: Comes with the well-built Celestron VX GoTo EQ mount (by itself this costs $799 when not on sale), and Celestron's 6" Newtonian (by itself $299). You will save $100 when you buy the bundle as the bundle cost is $899 when not onsale.
- Celestron XLT 150 OTA: This is the telescope only. Great optics. Great mechanics, too! You will notice 150mm = 6" roughly.

3.) Catadioptric telescopes use both (a corrector) lense and a mirror. In terms of pricing, it is common wisdom that these are between reflectors and refractors in terms of price. This is also where it gets a bit more complicated. There are 2 common types of catadioptric telescopes. The so-called "Cassagrain" design uses a corrector lense in the front, a primary mirror in the back, and a secondary mirror in the front where the corrector is to reflect the light back to the back of the telescope. This light-folding pattern leads to very compact OTAs.The 2 flavors are Schmidt-Cassegrain and Maksutov-Cassegrain. The main difference between these 2 scopes are that in the case of the mak telescope, the corrector is a meniscus type lense, and the secondary mirror is just the silvered central part of the meniscus lense. It is said that the smaller obstruction in mak telescopes leads to better contrast at the cost of more magnication/but smaller fields of view. Walking into a telescope store, and online, the potential buyer will quickly come across the Celestron NexStar or Evolution Series. These are the models I looked at from a very beginnery point of view. Obviously, the more money you have the larger you would want to go (up to 8" in my opinion). I will only list the Nexstar versions here as they are more cost-effective. But if you like very techie products with things such as local wifi, phone and tablet control features etc, look to the Evolution series. Be aware though these features will likely cost you at least $200 more compared to an equivalently sized Nextstar model.

Celestron Series (below are the models I was mostly considering for costs and portability):
- Celestron Nexstar 4SE
- Celestron Nexstar 5SE
- Celestron Nexstar 6SE

Orion sells Maks:
- Orion Starseeker IV 127mm

There is some discussion going on as to the FoVs of these telescopes. Fact: The FoVs will be narrower than comparable Newtonains or refractors. This is the reason why all these systems mostly come on computerized mounts: with narrow FoVs, a new beginner would quickly lose patience finding objects without computer help. The open question is: With computer aid, are narrow fields of visions a drawback. There is a different thread for this discussion. In this thread, I am just raising this as a point the potential buyer should be aware of.

In my search what I found most surprising was that there are other variants as well, things like: Maksutov-Newtonian, or Schmidt-Newtonian. You will guess from the name that these scopes are essentially newtonian telescopes with either the Schmidt or Mak version of a corrector. Their main advantages are that these plates can correct for "aspherical abberations" very well - something standard, larger Newtonians are prone to. An example of that sort of scope can be found below:

- 152 Comet Hunter Maksutov-Newtonian: 6" OTA. Cost when not on sale $699. You will need to buy a solid tripod/mount to go with this OTA. Since I want a GoTo mount, I would have to consider the VX mount which runs another $799. For a beginner, I feel that this is pushing the outer boundaries of initial costs. The upside is that this scope + proper mount would last a long time.

I will end this post by pointing out that in addition to the scope, one should plan in a budget to buy at least 1-2 additional good quality eye pieces and a barlow lense. This last statemen in itself could be a whole new chapter of discussion. But since this post is already pretty long, I will keep it short and end it here.

Anyway, this is not the end-all, be-all guide, but perhaps this sharing of what I have found so far will be useful to other new community members also on the hunt for the holy scope :-)