[aad_Dira]

thank you really very much again!

Originally Posted by mental4astro

The other thing that governs the comfort of viewing the moon and planets is that they can be really bright, especially the moon. If you only get one filter, I would suggest a polarising filter set. These are two polarising filters that you then use to vary the amount of light getting through. When I do view the moon, this is what I use.

There is an astro retailer here in Sydney that sells these polarising filters for $19 each. Purchasing two will make this polarising filter set. Look in the heading of "Guan Sheng" towards the end of the page is the filter selection:

http://andrewscom.com.au/site-section-10.htm

Under the "General Accessories" is a selection of inexpensive colour filters. The link to the Lumicon filters is not intended as an advertisement for them, but to show you what the various filters are designed to do and what they will help show.

so, do you mean that the variable polraizing filters is the best for a beginner? and what is the good amount of light reducing for me? is 1 to 40% good? most of the filters i have found have this amount light reducing.

A scope of the size you are looking at, 3 or 4", is still good for DSO's in the city. I live in Sydney, so my sky too is very light polluted. I started with only a 2" scope, and learnt how to make the most of things with it. I often observe with my 5" scope from home, not just with the17.5" as the 5" is really quick to set up. Open clusters, globular clusters, and bright nebulae are still observable, even from Jeddah City, . There is even a number of galaxies too that are within the range of scope you are looking at, from a city observing site.

you are really "refreshing" me. but there is another point, that is you are observing in Sydney from a southern sky, but i am here observing from a northern one. i don`t know how much it is different, but here i think that the brightest nebula is Orion nebula, so, other than it and Andromeda and its staellites, i don`t think that there is a nebulae or galaxies less than 8+ mag in our sky, at least very few.

The main thing is to try to shield the site you are observing from, from strong direct lighting, like street lights and the neighbours flood lights. This alone will improve things imensely. This will reduce stray light affecting the optics and help to preserve you night vision as much as possible. A good stable mount is another to dampen quickly vibrations.

thank you for this information. i can note how much this is useful because usually when i look to the sky and the is a direct light next to me, i can`t see anything before i shield it by my hand (and when i do that i can see many stars). but i has not thought before about doing this with the telescope..

The only filters that will help with DSO's are those designed for nebulae. But because they are very selective in the spectrum they let through, they are not useful for anything else, like galaxies or clusters, as they glow across the entire range of the light spectrum. In the city, these filters do help a great deal with viewing nebulae. They can actually make a real difference in see them or not, and even identifying things like planetary nebulae from the background glow. And yes they can be expensive, but it is something then you can save money for.

but, the nebulae is a faint object, and the filter will reduces more of its valuable light, why it is still good for the city observations? and even your saying that "They can actually make a real difference in see them or not".

You say that your eyesight might not be the best, that is not a problem. That is why I mentioned this example. My 40 year old eyes are not as good as a 17 year old's, but as I said, it is experience, .

that was just a joke! .

There is one other thing I can suggest, that is using a pair of binoculars when you are using your scope. These will allow you to see stars that light pollution rubs out when you are trying to find your way around the sky with star charts. The best thing is that it should not be hard to get your hands on a cheap second hand pair. I use mine every time in Sydney, and from a dark site, they make for beautiful wide field telescopes. The 'classic' astronomical size is 7X50mm.

i already have a binocular, but it is not useful with nebulae, just for stars.

Is there an astronomy club near you? They might hold regular viewing gatherings where new comers would be welcome to look through the various instruments. This will help give you an idea of what different scope sizes offer, and what good quality accessories can do. You might even be able to find a scope that someone might be selling. The folks there will be able to help answer the many questions you will have too.

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there is just a near unactive astronomical society in my city, so this is not very possible.