If you own a telescope, you must know what is a Barlow lens. It’s invented by Peter Barlow (1776-1862), an English writer on pure and applied mathematics. Barlow lens is a concave lens which is place between the primary mirror of telescope and eyepiece to increase the magnification of the eyepiece which is currently used.
A 2X Barlow lens is widely found in the market. It doubles the magnification of your eyepieces, thus it’ll double your collections of eyepieces. It saves your money! When you choose your Barlow lens, you must select the Barlow lens which is same with your eyepieces in barrel sizes. For my LX90, it uses the 1.25″ format of barrel size.
If you can manage to buy a Barlow lens with better coating, go for it! It’s because if the light transmission of the Barlow lens is bad, increasing the magnification just doesn’t worth it.
Where to put the Barlow lens? It’s quite simple to use the Barlow lens indeed. First, install the eyepiece holder. Afterthat, drop in the Barlow lens and following by the eyepiece. Then, you got it!
Finally, this article has entered the last episode! I myself love the catadioptrics the most because it’s considered lighter than most of the others. One of the reason is they are always mounted on altazimuth mount instead of equatorial mount which is heavy since it has to be equipped with counter-weight. 
Catadioptrics use a combination of mirrors and lenses to fold the light and form an image. Catadioptrics are the most popular type of instrument, with the most modern design, marketed throughout the world in apertures of 3.5 inches and larger. There are two popular designs of these mirror and lens hybrids, i.e. the Schmidt-Cassegrain(right top) and the Maksutov-Cassegrain(left down). I myself own a Schmidt-Cassegrain. 
Let’s start the introduction of both types of telescopes! 
Continue reading ‘Select Your First Telescope (Episode IV: Catadioptrics)’
Reflectors usually use a concave, parabolic primary mirror to collect and focus incoming light onto a flat secondary mirror that in turn reflects the image out of an opening at the side of the main tube, into an eyepiece for viewing.
The easiest way to identify a reflector is by looking at the location of its eyepiece holder. It’s always near the top of the telescope itself.
Let’s look at the advantages and disadvantages now. 
Reflector
Advantages
Lower cost per inch of aperture than refractors and catadioptrics because mirrors can be produced at less cost than lenses in refractors in medium to large apertures
Reasonably compact and portable
Excellent for faint, deep-sky objects, such as remote galaxies, nebulae and star clusters, because of their larger apertures
Deliver very bright images with few optical aberrations.
Disadvantages
Not suitable for terrestrial observation
Slight light loss due to obstruction from the secondary mirror
Tomorrow, I will write about my favourite, the catadioptrics as well as the conclusions of these episodes!
I have mentioned that there are mainly 3 types of telescopes. They are refractors, reflectors and catadioptrics. I am going to tell what are the advantages and disadvanges of them. I hope you can make up your mind after reading this article. 
By the way, the long contents made up my mind to divide this post into total of 4 episode. Sorry for the inconvenience caused. 
I am going to list out the advantages and disadvantages of refractor now.
Refractor
Advantages
Simplicity of design contributes to ease of use and reliability
Require little or no maintenance
Excellent for lunar, planetary and binary star observing, especially in larger apertures
Good for distant terrestrial viewing
Offer high-contrast images with no secondary mirror or diagonal obstruction
Render good color in achromatic designs and excellent in apochromatic, fluorite and ED designs
Sealed optical tube reduces image-degrading air currents and protects optics
Have permanently mounted and aligned objective lenses
Disadvantages
More expensive per inch of aperture than reflector or catadioptrics designs
Heavier, longer and bulkier than equivalent-aperture reflectors and catadioptrics
Cost and bulk factors limit the maximum practical aperture size
Not very suitable to view small and faint deep-sky objects(DSO) because of the limitations of practical aperture.
Let’s continue the list of reflector tomorrow.
Today, I am going to write an article of Select Your First Telescope. I am going to divide them into two parts. This episode will tell you what you should take caution of the specification of the telescope.
It is really confusing for us to choose a telescope. There are mainly three types of telescopes which are widely sold. They are refractor, reflector and catadioptric. The telescope shown at the right is a Meade 8″ LX90(catadioptric).
Continue reading ‘Select Your First Telescope (Episode I)’
Yesterday, there was a special celestial event! I am sorry that I didn’t tell you all about this event. It’s the Pleiades occultation!. At first, let me tell you what is a occultation. Before I start, let me show you a photo of the Moon eclipses the Pleiades.
An occultation in Astronomy is always linked with Moon. If I say the moon will occult Mars, it is meant that the Moon will eclipse the Mars. Let’s say an “eclipse” of the Mars. What about an Orion (a constellation) occultation? It is the Moon eclipses the Orion. So, do you get it?
What does the occultation offer to the astronomers? In the old days and nowadays, occultation helps astronomers to divide a binary star. Astronomers also spotted that the Moon doesn’t have any air. If it has an atmosphere, stars will be dimmed when the Moon moves near them.
Let’s back to the main topic. The occultation of Pleiades was happened from 9.30pm to 12.30pm (PST or GMT+8). I was planning to observe this amazing event but sadly, the sky was cloudy. Anyway, I found a photo gallery with 6 pictures of Pleiades occultation. Let’s enjoy them!
Gallery of The Moon Eclipses The Pleiades
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