Saturday, April 26, 2014

Celestron 70az: What can you expect to see?

When someone buys a new telescope his first question is what i can see with it. The second is what is the highest zoom i can achieve. Although the maximum zoom can be an attractive measurement when buying a new telescope, the buyer should focus on the aperture size: how much light i can gather? This is the main difference from theoretical to practical highest zoom.

So, what can you expect to see with this telescope?

During the tests i did, the average seeing conditions with medium-low light pollution. These two factors can really improve your experience or.. to destroy it. In my place i would categorize the light pollution in class 5, based on Bortle 's scale. I also tried to improve the lenses by blackening the edges, as i described in earlier post.

A quick note here before discussing my personal views on the topic. Planets and stars have different brightness that we call it apparent magnitude. Lower the number is, brighter the stellar object is. The practical limit of the telescope is around 10 as it is expected by a 70mm telescope. Here is a list of famous stars and planets:

Apparent Magnitude of celestial objects Source: ESA
Apparent Magnitude of celestial objects Source: ESA

To calculate the achieving magnification of the telescope we use this equation: 

magnification = focal length telescope / focal length eyepiece

In our case the telescope has 900mm length, thus we always divide this number by the length of the eyepiece. Here is a table describing the achieved magnification (zoom) in combination with a barlow and some comments from personal experience. 

Tube Length (mm)
Eyepiece
Barlow ( 1X – 2X)
Zoom
Comments
900
32
1
28,13
Wide view, best for star gazing
900
32
2
56,25
Good for star gazing and big planets
900
20
1
45
Wide view, good for star gazing.
900
20
2
90
Lot of light. Stars and planets.
900
15
1
60
Good for star gazing, less light than 20mm
900
15
2
120
Loosing a lot in contrast, but acceptable
900
10
1
90
Less light, but acceptable for stars
900
10
2
180
Telescope limit, bright planets only
900
6
1
150
Telescope limit, bright planets only
900
6
2
300
Unacceptable, even during the day

In short: if you want to use the telescope for star gazing you should use magnification up to 100. For planets, you can go up to 180x, but you are going to loose a lot in terms of brightness. Anything more is unacceptable! In the future, i will make calculations what are you loosing in terms of brightness.

Friday, April 18, 2014

Improving the Celestron 70az

Recently i was looking to buy a second smaller telescope, ideal for traveling. I concluded on Celestrron Travel scope 70 that has the best value for money. During my research about the quality and the characteristics of the scope, i  came up to a page that was commenting how to improve the quality of the scope.

Here are some thoughts about my scope:

- The quality of the tube is slightly better, but still it has some issues.
- You also have some bolts inside the tube, but not  many as the travelscope.
- Collimation is an issue also here. You should use a collimator to fix this. However, in my case i wanted to avoid buying anything new.
- Lenses are not blackened (neither in eyepieces)

Collimation without tools:

Collimation is usually not an important issue in refractor telescopes compared with the reflector, but it can improve the views and the experience of star gazing. You have to disassemble the telescope without caution. Take care the lenses!

The easiest way to fix the collimation issue was to focus on a bright point (star or something small) with 10mm eyepiece or less and adjust the lenses. In my case the problem was on the ring that keeps the two lenses together (the objective lens). The ring was too tight screwed, i relaxed it a bit and the viewing quality was improved.

Lenses blackening 

The second step of improvement was the blackening of the edges of lenses. Astromaster telescopes are not expensive telescopes, thus you should not expect good premium lenses. The  first step was to disassemble the tube and remove the lenses:

Lenses of the Astromaster 70 before blackening.
Lenses of the Astromaster 70 before blackening.


The second step is to paint black the edges. Note that you have to paint even the small space between different edges, or else you will still have some light scattering around. Note the next picture:

Painting black the edges of the lenses. You have to completely black the lenses because some light will scatter around.
Painting black the edges of the lenses. You have to completely black the lenses because some light will scatter around.


After finishing the painting we have to put them back in the tube. Note that is extremely important that you keep the parts in the right order and also facing the right way, or you are risking damage to the glass.

After blackening the lenses of my telescopes.
After blackening the lenses of my telescopes.

After finishing with the tube's lenses you can move on on the eyepieces. Unfortunately, you can't disassemble most of the eyepieces, but you can disassemble the 20mm bundled with the telescope. Again, here you must be careful with the dissemble to avoid  damaging the lenses:


Parts of the 20mm eyepiece coming with the Astromaster telescope. You can blacken the two lenses.
Parts of the 20mm eyepiece coming with the Astromaster telescope. You can blacken the two lenses.


Then, you should pack everything and you should test everything during the day before actual live testing on the night. It is not easy to 'debug' the lenses in the night without light. I suggest to test lenses with a different part each time. For example, you can use your favorite unmodified eyepiece with modified telescope tube to test the result:


Celestron Astromaster with 2X magnifier and 30mm eyepiece.
Celestron Astromaster with 2X magnifier and 30mm eyepiece.

Happy star gazing!!



Monday, April 14, 2014

First steps in astronomy



This post is dedicated to one of my hobbies: astronomy. When i was little kid i was getting inspired from the stars, the planets, and space in general. Later i found my self reading late in night about light speed and time paradoxes. So, last year i said, ok why not looking at the stars using telescopes? Telescopes are not so expensive (small ones) and there is plenty of information on the net to start playing with them.

I decided to go with a Celestron 70AZ Astromaster. I selected refractor because it has less maintenance compared with the reflectror (in reflector telescopes, everything must be aligned properly and the mirror loses its reflectiveness by time). After using the telescope for a couple of nights i realized that i should have selected the eq version, as it has better tripod. Moreover, sometimes i 'm missing... light: the telescope is very small for deep space objects, such as nebulas or nearby galaxies. The 90eq was more proper in this case.

Among with other parts i bought also a small set of filters and eyepieces, but nothing expensive. Later i bought also a 32mm eyepiece because i wanted to have a winder view of the stars. A moon filter is necessary as it hard to see it through the telescope due to high brightness. In one of my next posts i will describe my first set of eyepieces, and to give you an idea what to expect with this telescope.

UpClose G2 10x50 Porro Binocular
Celestron Upclose G2 10X50 Porro

Apart of that i had one more tool to play with astronomy. Telescopes have really small field of view, starting from 2.5* and going down to 0.9* or less. For this reason i bought a chap set of binoculars: the Celestron Upclose G2 10X50 Porro model. 10 goes for the zoom and 50 goes for the diameter (in mm). Going for bigger binoculars requires the usage of tripod. Even with mine mid-powered  set i had problems, just imagine using some monsters of 12x70.


The last, but not least tool i used was the  sky map of google in my smartphone. It is really help full especially in the first days, that i didn't have any idea on what i was looking. Later i started also using star maps and the Stellarium program to identify the star constellations.

What ever you choose as a first equipment at the beginning you will need only your eyes and... a clean dark sky (not so obvious to find...).

Here is a first picture of moon using my point and shoot camera and the Astromaster 70AZ:

A photo taken using point and shoot camera and the Astromaster 70AZ and 20mm eyepiece.
A photo taken using point and shoot camera and the Astromaster 70AZ and 20mm eyepiece.



Thursday, April 10, 2014

Taxes in Greece as self employed

It has been almost four months that i came back to the beloved Greece. Recently i started working for an UK based company, OnApp. The prospects were good: a good salary combined with the sunshine of south Greece. However, after some time i realized that the taxes where insane high. To get an idea lets assume two people with gross salary 2000 and 3000 euro per month. In both cases you don't need to pay VAT (23% now in Greece) as you provide a service to a company and the company will produce the product to the final customer.

So lets see an example of tax:



Gross Income per year
24000
36000
Technical Chamber of Greece1
-100
-100
Insurance + Retirement
- 2706
- 2706
Tax (26%) without ins + ret
- 21194*0.26 = -5510.44
- 33194*0.26 = -8630.44
Prepay Tax (55%) for next year2
- 5510.66*0.55 = -3030.74
- 8630.44*0.55 = -4746.74
Total After Main Tax
12652.82
19816.82
Solitary tax (1-4 %)3
-6,52
-78,168
After all taxes
12646
19739,39
Tax + overhead
47,03%
45,16%


1. Depending on the employment category. Some categories can ignore it.
2. Only the first year! 
3. 12001 - 20.000,99: 1%, 20001 - 50.000,99: 2%, 50001 - 100.000,99: 3%, 100001 and up: 4%.

So, what is different compared with many other countries: 
  • You prepay the 55% of the tax for the next year. The tax service assumes that you are going to have the same income next year. So, the tax is 1.55X
  • Insurance and retirement is fixed no matter your income. This changes by the year you are self employed.
Another issue that you have is that you have to pay more as you are getting older for the insurance and retirement. You change in category after three years. Here is a table with different categories:

Category
Retirement
Insurance
Unemployment Benefit
Sum per month
1
152.41
58.30
15
225.71
2
186.14
71.20
15
272.34
3
222.20
84.99
15
322.19
4
242.58
92.79
15
350.37
5
279.81
107.03
15
401.84
6
315.59
120.71
15
451.3
7
337.46
129.08
15
481.54
8
364.90
139.57
15
519.47
9
389.55
149.00
15
553.55
10
414.22
158.44
15
587.66
11
438.87
167.87
15
621.74
12
463.52
177.30
15
655.82
13
488.19
186.73
15
689.92
14
512.85
196.16
15
724.01

For example, if you are working for 18 years,  you have to pay 451 per month, in total 5412 per year. This overhead can be really big especially, if your income is not so high. The last, but not least issue, that someone has to encounter is that the laws and tax rules change every year. Thus, it is very hard to have a financial plan for the next two-three years.  On the good side is that you can include expenses and not taxed for them. For example, you can buy a new laptop, a new monitor, or a new phone. If you rent an office you can also put the rent in the expediences and not pay tax for them. Things can be much worse if you open a business: the registration and anual fee of technical chamber increases a lot and you have to prepay 80% of the next year's tax. Furthermore, you have to pay also VAT when you sell products of provide service.

So, if you thinking working in Greece and you got a good offer, please make your calculations before coming. At least they can't tax the sun :).


Update 1: Inserted solitary tax (not sure if this is the proper translation) and some information about the technical Chamber