A beginner's guide to cassegrain telescopes

A blog on the universe and the cosmos above and the nature of it determined by great scientists.

Cassegrain telescopes are specially designed telescopes which were first made in 1672. These telescopes have both concave and convex mirrors. These telescopes work on the simple laws of reflection in which the light is reflected by both the mirrors and then reaches the eyepiece.

• Cassegrain telescopes and how they work
  
• Usage
• Schmidt - Cassegrain & Maksutov Cassegrain Telescope (MAK)
• Buyer's guide

Cassegrain Telescopes :

                      Cassegrain telescopes are one of the 2 main types of reflecting telescopes that we use. Reflecting telescopes are the type of telescopes that use concave mirrors to reflect the incoming light and give u a clear picture of the skies. By using concave mirrors, these types of telescopes overcome the difficulties of size and mainly colour errors.

Construction of Cassegrain telescope :

The mechanics of cassegrain telescopes

[ Zoom in if you can't see ]

                    So the above diagram is a diagrammatic representation of how a cassegrain telescope works. If you see closely you'll find that the construction is unique. The Cassegrain telescope uses both concave and convex mirrors. For your ready reference, Concave mirrors are the ones which are curved inwards and away from incident light rays, while the Convex mirrors are the ones which are curved in the direction of light, that is outwards

                    In Cassegrain telescopes, the light rays coming first hit the Concave mirrors, and as mentioned above the concave mirrors are curved inwards due to which the incoming light gets reflected. These concave mirrors are adjusted to a specific angle such that the light reflected straight falls on the concave mirror. The reflection of light is denoted by arrows in the above diagram.

                    After the light hits the concave mirror, it gets reflected inwards towards the eye piece. This happens because convex mirrors are curved outwards as mentioned above and thus when light hits its surface, it is reflected inwards. Even the convex mirror is positioned in specific angles such that the light reflected moves in the direction of the eye piece. Once the light hits the eye piece you can view the clear magnified image of the sky.

Advantages of using Cassegrain / reflecting telescopes : As described above, these telescopes use mirrors instead of lenses for reflecting the incoming light. As said above, these telescopes use large mirrors to reflect the light giving you a much larger and clearer picture. Also large mirrors are easier to make and hence less costly as compared to large lenses, making cassegrain telescopes cheaper. These telescopes are designed such that you don't face any colour distortion. These types of telescopes have a very high magnifying capability such as to you can even see the milky way in the night sky.

                   These telescopes are comparatively easier to mount up and set in as compared to the refracting telescopes. There is a tutorial below in the usage section if you want to learn how to set and mount these telescopes. So if interested then scroll down to the usage section.

Usage :

                    Like all other telescopes, the most obvious use you are going to make of this Cassegrain telescope is sky watching. So if you are using it for sky watching then below are 5 useful tips for your :-

1. Setting up : The first thing you need to learn after buying a Cassegrain telescope is to mount it up. There are various important parts of this telescope that you need to fit in properly in order to get a clear picture of the sky.

2. Cleaning : You need to take care of the telescope parts while maintaining and cleaning the telescope. Especially if you have not used the telescope in a while, then you are bound to notice dust settling on top of it and you may consider cleaning your cassegrain telescope.

                    In such situations or in fact at any time if you are cleaning the telescope, then it is advisable to use a lens cleaning cloth which you would probably get while purchasing the telescope. You should not use any kinds of gels or cleaning liquids on the telescope even in your wildest dream. If you do so then there is a very high chance that the telescope may get damaged and result into degraded quality of viewing.

3. Mounting and positioning : You always have to mount this telescope perfectly and carefully as we discussed above. Now even the positioning is an important factor. Positioning the telescope's axis at the northern celestial pole can help. If you are having a modern version of the Cassegrain telescope, then it may have degree wise rotational feature which you can set up at the northern celestial pole.

4. Star trackers : So Star trackers are tracking devices which will help you identifying and focusing on certain celestial objects based on their average appearances. A Start tracker is not necessary but may help you to get a quick glimpse of the perfect celestial body you have been looking out for.

5. Camera : You can also set up a camera to get some great images of the skies above. Though this process is a bit complex and I haven't tried it ever, I suggest you to click here to get a video tutorial for setting up cameras on your telescopes for astrophotography.

Schmidt - Cassegrain [ SCT ] & Maksutov Cassegrain Telescope (MAK) telescope :

                    The Schmidt - Cassegrain telescope is a kind of sub type in the famous Cassegrain telescopes which were first invented in 1672. The name of the other sub type is Maksutov cassegrain Telescope (MAK).

Schmidt Cassegrain telescopes [ SCT ] : The basic Cassegrain Telescope design is the only common thing these 2 sub types of this telescope. The correction plate which makes corrections in the picture produced to give you accuracy is flat in this sub type. Generally this correction plate is the convex mirror in the above diagram. If you closely observe, the convex mirror in the diagram is not flat but it is in
Schmidt Cassegrain telescopes. This type of design allows the opening for light to enter the telescope to widen up due to which you can observe a larger picture.

Maksutov Cassegrain Telescope (MAK) : The above diagram refers to a Maksutov cassegrain Telescope. In such design the convex mirror is curved and also thicker which makes the opening of the light passage of the telescope much smaller as compared to Schmidt Cassegrain telescopes. However on the flip side of the coin, these telescopes provide you with a much sharper and brighter image of the sky. These telescopes are much convenient and cheap as compared to SCT.

Buyer's Guide :

This product by Barska makes it to my top of the list due to its amazing attachments, low price and efficiency.

The only thing that you need to pay attention to is if you are searching for this product on amazon then you may not get it, so follow the link provided below in box to buy it. It is transported and sold by Tanotis which is an Indian origin reliable company.

This telescope is pretty easy to assemble and also for use. It has a refractor of about 400mm and comes with 2 of interchangeable eye pieces.

 This product is very convenient to use and can be used to observe the skies at an unparalleled level. And then with its very low cost which adds up to its value.

Value : 9/10

                   

So this product is a Maksutov Cassegrain Telescope and makes the second position on my list. The reason why it stands out is because of its amazing 1200 mm focal length.

This product comes with a finder scope which is an additional can choose to put on the top of your telescope.

The reason why it is not first on my list is its pricing. Yes it has a very high focal lenght and can help you get an amazing view of the cosmos, the price isn't worth it if you use it casually.

For professional astrophotographers and others who do sky watching as a profession, this telescope is on the top of the ladder.

Value : 8/10

   

                    The image aside is of a Newtonian telescope available on amazon.Its ranking on the third position because it is just back by a finger space when compared to the 2nd product. This one can be used for casual use more than professional.  One advantage is that it comes with a free mobile stand with it. It has got to eye pieces so that you can always keep one for spare use.

Value : 8/10

   

                    The fourth on my list is a Celestron product. This product is very handy and easy to use.

It has certain backdrops as well. As compared to the previous product on our list, this product has 70 mm optics while the other one has 1300 mm. So the view that you will get will differ by an extent.

In the price wise comparison, this product stands out pretty clearly. This product is very cheap but as said above, the quality will differ.

value : 7/10

   

                    Finally on the last position of my list, I am having this another celestron product which is brought to you by Tanotis. This telescope is also a Maksutov Cassegrain Telescope. This product comes in with a steel tripod. It is also equipped with great quality finder scope which you can adjust on you telescope if wished.

The thing which is not common between this telescope and the others, is that this one is computerized. But due to this quality, the price of this product is a skyrocketed one. I searched for several other computerized telescopes but this is the best and the cheapest of them all.

The only reason due to which it lies last on my list is due to its price. The products mentioned in the second and 3rd positions basically satisfy almost all needs of the telescope even if you want to use it for professional purposes and due to this reason this product is at the end of my list.

value : 6/10

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