Building my first Telescope

[Nitin]

Hello guys,

I am a beginner on a tight budget (~10,000 Rupees).

Initially I was looking for my first scope (a reflector) ~114/130 mm primary, but my budget limited my choices to not-so-stable EQ1 mounts.

So, after spending a lot of time on how a Dobsonian is built, I am thinking on making one myself with 150mm mirror.

Please help me decide on below choices available at a retailer nearby:

1. 150 mm Fl. = 750 mm

2. 150 mm Fl. = 1000 mm

3. 150 mm Fl. = 1200 mm

Also planning to buy at least 2 eye-pieces and a Barlow, please suggest the matching ones.

[nmoushon]

I've never built a scope before but from what i've heard and read that the faster f/ratio the harder it is to make the mirrors. Now with that said I know people make F/5 Dobs all the time so opt #1 is very doable and is a common choice thats out there. Though me personally I think I would lean a bit towards opt #2 just for the extra bit of FL. F/6.7 isnt that much slower than F/5 and I think would work great. The FL isnt to long to give you a very narrow FoV (depending on EP of course) but is long enough to help give some detail to some of the smaller objects out there. So for opt#2 I would also pair it with a nice wide EP in the 25-32mm range and then one a bit higher mag about 15-20mm on top of a 2x barlow. This would give you 4 possible mags that are spaced out evenly enough to give you options to view with. Just my thoughts though.

[dweller25]

The 750mm is an F/5 and is designed more for imaging it will require a larger secondary than the rest.

The 1000mm is an F6.7 and would be a good all rounder (deep sky and planets)

The 1200mm is an F/8 and is ideal for the planets as it requires the smallest secondary thus giving the least obstruction and the most contrast.

For the eyepieces you need to give more info about the type of observing you do and which of the focal lengths you select.....

[Nitin]

nmoushon, thanks for reply.

First a clarification, I am purchasing the ready mirror, and the cost is not varying much between the three options.

Secondly, I see Orion and Skywatcher have F/8. Should I follow that as a reference ? And can you also give EP options for this one.

[crashtestdummy]

I would go down the 8" 1200mm route but surely the skywatcher 200p can't be much more than making one?

[Nitin]

dweller25, thanks for helping out.

I am not into imaging. But yes, interested in deep-sky objects.

Please suggest some EPs for option 2 & 3

[dweller25]

For the 1000mm - a 20mm eyepiece plus a x2 barlow giving x50 and x100

For the 1200mm - a 25mm eyepiece plus a x2 barlow giving x48 and x96

[Nitin]

I would go down the 8" 1200mm route but surely the skywatcher 200p can't be much more than making one?

I started with a budget of 10K, and this build will cross 15K for sure.

Talking about skywatcher 8" 1200, thats 38K here, and for build option, 18K for mirror alone.

And BTW, this is my first build attempt. If I like building it this time, I will go a step forward and do the grounding myself next time.

[dweller25]

Nitin - there is a lot of info on the internet to assist you in building the scope, good luck and we want to see pictures of the finished scope.......

[nmoushon]

Definately look around to see if their are any astronomy clubs near you. Even if you have to travel a bit for a weekend get together it will be well worth it. You will find a lot of help.

[Nitin]

Thanks for helping guys.

And yes I am constantly looking at the online resources.

But the things slowing me down will be getting the Mirror. The retailer I mentioned above is 1000 km away.

Can't just order online and wait, will have to go there with a set of questions on the items.

Any advice on the quality of the primary and secondary mirrors ?

He does mention 1/6 wave with the mirrors. Is that good enough ?

I will share the pictures of the scope when its done.

[Schorhr]

Specifications are one thing, reality the other ;-)

With the 1200mm focal length the quality is most likely to be best, parabolization errors will not be as disastrous as with a f/5 mirror.

If you can get a large drain tube at the hardware store, you could get it built cheaply. But usually the six and eight inch dobsonians are so cheap building only makes sense if you can get the optics really cheaply. 

See pictures in this german forum http://www.astrotreff-deep-sky.de/ATDS_postst8886p2_Anfanger-braucht-Hilfe-Spiegelteleskop-Selbstbau.aspx .

As you seem to be on a budget, get a 30mm, 10mm Plössl (15/10€) and a 2x achromatic barlow (€13) for example. Seben erfle or plössl are rather inexpensive, sometimes those cost twice as much or more. I am not sure what's available here...

If all fails you can surely get used 10 and 25mm eyepieces verrrry cheaply to get you started, as those are sold with a lot of telescope sets from skywatcher. Those are not great but better then toy telescope plastic eyepiece.

The 66 degree widefield eyepieces are more common though and start at around 24€ if you order them in china including world wide shipping. You could get the 20mm and 6mm or the 20mm and 9mm plus a barlow.