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[mad4mars]

hi to everyone this is my first post and looking forward to all of your help and getting to know you.

basically i have just bought a seben reflector newtonian 150 x 750 x 1400
and i am so suprised how hard it all seems declinatiom screws being parallel with the polar axis , celestial north,lattitude ,i have just ordered a book "turn left at orion's belt",
can anybody help me with all these meanings and how to set the telescope or is it just point and look i really havent got a clue,any tips will be met with such gratitude,
coz i really am lost in space

regards

[Michael Steen]

I've been looking online at reviews of Seben (a company I'd never heard of). Did you buy this on e-bay? Did you read a lot of reviews of this and other scopes before you purchased?
A good company should have sent you pretty extensive documentation about using the equatorial mount and aligning the polar axis. Did you get it?
"Turn Left at Orion" is a fine book for finding objects in space, but it has nothing in it about using and adjusting a telescope.
By the way, what do the numbers 150, 750, and 1400 mean? If they are magnifications, you can forget about the last two. It's never going to happen.
Please write back with more detail, and I'm sure some people here will be more than happy to give you a hand.

[mad4mars]

hi there thanks for the reply
yes i got it from e bay but did a bit of looking before i bought it yes i do regret not buyying the celestron that was advertised next to this one i have been in contact with seben and they claim to have sold these world wide and i asked them for charts or software but they dont sell it.
as for the book i emailed a few company's and they recomended orion's belt,it becoming quite clear that people will sell you crap to make money.

info is a short tube newtonian equatorial reflector telescope
d = 150mm f = 750mm and f = 1400 ????????????????

regards

[admin]

Hey Mad4Mars,
sorry to hear about that.

have you seen anything through your seben reflector newtonian?

cheers

[mad4mars]

hi there
yes last night we had a good clear moon so i gave it a go and it was really clean and clear i used the plossl 25mm af 40 deg but failed to use the barlow x2 lens again it could be that i am new to this and will get better in time and with help from people in the forum i have just downloaded google earth 4.3 which has helped and was hoping this book i bought may help but it seems it dont tell you how to set it up ie assention declination again any help would be great or would it be easier to get a new scope that wil suit me more
trust me i aint stupid but i dont take things in quick by reading im better with verbal info .
again thanks to you all who have replied this is a great forum

[Carlos_dfc]

Hi

Yes, 'Turn Left at Orion' is probably THE best book for a beginner, to show you where to find a good selection of stuff to get you started - it also shows what you can expect to actually see through the telescope, and explains exactly what it is you are seeing.
[Registered users can see links. ]
Along with 'Turn Left' - I also always recommend a book called 'NightWatch' by Terence ****inson to beginners.
[Registered users can see links. ]
This book has a few all-sky charts in it, but where it really excels, is it's explanations of how to actually align, and use a telescope. Also with explanations of telescope terms, eyepieces, binoculars, mounts, and all other kinds of equipment.

As for your own telescope Mad4Mars, Yes, Seben aren't the greatest, but it's down to your own personal preference whether you want to spend more on a better scope.
What I can tell you is what those figures mean:
d=150
That's the diameter of the main mirror, in mm
This is the all-important specification of any telescope, usually referred to as the 'aperture'. It governs how much light the telescope gathers, and also the upper limit of the telescope's resolution. 150mm equates to 6"
What you have, is a 6" Newtonian reflector
f=750, f=1400
These are focal lengths - the focal length of a telescope is the figure you need, if you want to calculate what magnification you are using.
You simply divide the focal length of the telescope, by the figure on the side of the eyepiece (this is also the eyepiece's focal length)
Have a look into the focuser of your telescope - you will see that there is a lens down in the bottom of that tube - that lens is basically a barlow (yes, I know you may also have an extra barlow, but that lens in the bottom of the focuser tube is also a barlow.
In your telescope, the main mirror has a focal length of 750mm, and that barlow boosts it's effective focal length to 1400mm.
This is because Seben use 'spherical' primary mirrors (because a spherical primary is FAR cheaper than a 'parabolic' mirror) Spherical mirrors perform very poorly at short focal lengths (750mm is quite short for a 6" scope), so they boost the focal length to 1400mm (that lens in the focuser tube), in order to avoid the optical aberrations you'd get from a 150/f750 spherical on it's own.

My own 6" reflector ('SkyWatcher' brand) has a 750mm focal length, but has a parabolic primary mirror, which can perform well at such a short focal length - and so it doesn't have that little lens inside the focuser.
I do however, own a telescope of the same design as yours (spherical mirror, with barlow built into the focuser) - Mine is a Celestron 114mm f/500, boosted to 1000mm with that little lens.

This 'barlowed spherical' design does perform reasonably well at low magnifications (under 80x) - but as you go up the magnification, more aberrations become apparant around the outside of the field of view - also, at high powers, they become VERY difficult to get a sharp focus - this is becasue the design produces a very narrow field depth, which is also quite heavily curved.
The narrow field depth means that even the tiniest movement of the focuser will make a HUGE difference to the focus, so at high powers you may well be racking the focuser in and out several times, trying to find best focus.
And the heavily curved field means that when you get the centre of what you can see nicely focused, the edge of the field will be out of focus, then if you try to focus the edge of the field, you will throw the centre out of focus.
Rather than getting frustrated with this - If you have a scope of this design, it's far better that you accept it's limitations from the start, and don't try to push it beyond, say, 100x

Mad4mars - Using your 25mm eyepiece, you will be getting 56x magnification.
1400 / 25 = 56
If you add the barlow into that, you will be at 112x (the 2x barlow effectively doubles the magnification)
112x is a bit too much power for this design, so you will find that it becomes difficult to focus.
Did you get other eyepieces? - that scope USUALLY has something like a 12.5mm, 6mm or 4mm - if so, your other eyepieces probably also push the scope beyond 100x
1400 / 12.5 = 112x
1400 / 6 = 233x
1400 / 4 = 350x
Not only are these powers beyond the capability of a 'barlowed spherical' primary, the upper ones are also beyond the limitations that the atmosphere often puts on your viewing.
Most astronomers view deep sky objects between about 30x and 100x, and only really push further for close-ups of the Moon and planets, or for splitting tight double-stars - and most of the time, the atmosphere makes the image go all 'wobbly' when you start going much above 150x
I tend to view planets usually between about 180x and 250x, depending on atmospherics.
I have viewed planets at 300x a few times, with a very high quality telescope - BUT, only on very rare occasions is the atmosphere stable enough to do it.

If you want - you could try removing the little lens from the focuser, and see if the telescope is still able to focus your eyepieces.
If it does - you might find that the scope is more versatile like that.
With that lens removed, assuming you can still get focus, the 25mm eyepiece would give you 30x, and some of your other eyepieces might become usable.
Worth trying out - but make sure you can replace that little lens if the telescope won't focus when used at 750mm. (Careful not to break it if it doesn't unscrew easily)

I removed the little lens from my 114mm scope that I mentioned earlier - it now has a very short focal length of 500mm, and is good as a portable deep sky telescope - ideal for viewing my favourite objects - open clusters.
However, I'm under no illusions that it would ever be capable of high powers, and accept that it's only really any good up to about 60x or so.

Welcome to the weird and wonderful world of astronomy and optics.
I know it's a lot to take in, but in time you will come to understand all this stuff

If you do decide to get another scope - and if you decide on a 'Newtonian' or 'Dobsonian' design.....
Look out for the word 'parabolic' or 'paraboloid' reference to the main mirror.
Nearly all quality 'Newts' and 'Dobs' will have a parabolic mirror.

[mad4mars]

wow lol thank you very much for that the "little lens" you speak of what and where is that and yes i have a 6mm lens too.
with that in mind if you had around £500 to spend on a scope i basically want it to use to view the moon take photo's and look at our solar aystem ie saturn vega etc.what would you or anyone recommened

[Carlos_dfc]

Originally Posted by mad4mars

the "little lens" you speak of what and where is that

Remove the eyepiece, and look into the focuser - If it's there, it will be in the focuser tube, or possibly screwed onto the bottom of it.

[mad4mars]

thanks ever so much you have been a great help have you got any recommendations on scopes for that price range

[admin]

Mad4mars,
£500 can get you a good scope. It depends what you want to see. If you like deep space objects a light bucket like a 10" Dobson would be good, but if you want an easy to move scope with electronics (goto etc) then £500 will buy a smaller aperature scope

I am sure Carlos has a few recommendations as he is also in the UK