Got my first telescope! - an 8 inch GSO dobsonian

[Mountain_Wanderer]

Hi everyone,

Today I finally took the plunge and bought my first telescope! Finally, after years of thinking about it I finally have one!

I got a Guan Sheng Optical (GSO) GS-680 8" ASDX 200mm x 1200mm Dobsonian.

Purchased from Andrews Communications who were very helpful.

Features:
- Solid tube
- 8" primary mirror
- 1200mm focal length
- Focal ratio of F6
- Resolving power: 0.58 arc seconds
- Limiting magnitude 14.0
- Right angle correct image 8x50mm finderscope
- 2" dual-speed Crayford style microfocuser with 10:1 fine focusing
- 2" to 1.25" adaptor
- fan

Eyepieces (1.25" fully multi-coated plossl):
- GSO 9mm
- GSO 15mm
- GSO 25mm

It came with a bonus moon filter, which should come in handy on nights such as tonight!

I also got a Canon DSLR camera adaptor, Cheshire collimator and Skywatcher observing chair. This is in addition to the Andrews 11x70mm Binoculars and Skywatcher LED red light which I already have. Nice!

The scope is still in the box and I'm just about to unpack the beast! Awesome.

Just a few questions, if anyone can help?
- What magnifications will I get with each of the eyepieces?
- What are the Fields of View with each of the eyepieces?

It would be awesome to hear from anyone who has one of these scopes.

Clear skies!
MW

[raymo]

Congrats. First thing, have you verified with Andrews that that model has sufficient back focus to allow prime focus photography with your DSLR?
Many Newtonians don't.
Your mags will be 48x with the 25mm, 80x with the 15mm, and 133x
with the 9mm. The mag is simply the scope's focal length [1200mm]
divided by the focal length of the eyepiece , 9. 15, or 25mm in your case.
The field of view will depend on your eyepieces, as different eyepieces have different apparent fields of view, ranging from about 40 to 100
degrees.
raymo

[hobbit]

i believe magnification is telescope focal length divided by eyepiece focal length. Don't know about field of view

[Renato1]

Assuming that you have GSO Superplossls, they have a field of 52 degrees.

So the field of view you see through a telescope is 52 divided by the magnification.

So as your 25mm eyepiece gives 48X magnification,the field of view is 52/48= 1.08333 degrees = 1 degree 5 minutes

and you have an exit pupil of 25/ focal ratio = 25/6 = 4.17mm

Regards,
Renato

[Mountain_Wanderer]

awesome advice. thanks for this.

To update, unpacking is now complete. A few points to note.

- There are no assembly instructions. However Andrews printed me off a set before I left the shop.
- The handle you attach to the base to use to carry the thing around popped out of its screw sockets the first time I tried yanking the handle. I'll have to get some long bolts with nuts to fasten it better.
- The fan comes with no batteries (you need 8 AA batteries)
- The advertisement on the Andrews website for the eyepieces says it comes with GSO 9, 15 and 25mm eyepieces. However, what was provided in the box was GSO 6, 9, 15 and a 30mm Super View. Very odd. As I am a newbie, can anyone tell me if this is a good or bad result?
- I also got an additional moon filter in the box (the Andrews guys also gave me one over the counter)
- Overall, the base appears to move well, all parts have been provided, the tube is on good condition etc.


Hopefully I'll take this scope outside in the next day or so to get first light :)

[Mountain_Wanderer]

Quick question, can I stand the tube on its end without the base? If so can I stand it on the end with the collimating screws or will that damage the primary mirror?

[rustigsmed]

Hi MW,

Congrats on the new purchase! that will last you for a long time!
I wouldn't worry too much about the 30mm it will give a wider view and in a dob that's handy as you don't need to nudge it as often.
you may not be able to reach focus with a dslr, but someone on here should be able to help point you in the right direction of what modifications you can do to make it happen. It might be a case of moving the mirror up by replacing the screws with longer ones.

Cheers,

Rusty

[raymo]

I think the handle on the base is for carrying the base only, not the
whole thing. The assortment of EPs is not really odd. Both the retailers
and manufacturers change their offerings of accessories from time
to time. The 6mm will be handy for high power viewing when conditions permit, and the 30mm is as good or better for low power sweeping of
the sky.
raymo

[barx1963]

Yes you can, but for storage it is usually best to store the tube horizontally. That reduces dust settling on the mirror. Outside while assembling I wouldn't stand it on its end as it may get dirt in the collimating mechanism. You will notice that the mirror end is pretty open to facilitate airflow, but dust can also get in that way. A simple shower cap can reduce that while storing the scope.
With the eyepieces, that is actually a good result. The 30mm Superview is a very nice widefield eyepiece. I have one and have started using it occasionally in my 20" as an extreme low power eyepiece.
The 6mm will probably only get occasional use as it fairly high power and need good conditions.

Malcolm

[CJ]

Hi. I've got one of these scope too, as have quite a few others on this forum.
Mine came with a 1.25" 25mm Plossl eyepiece instead of the 30mm EP, which I assume is a 2" EP. I have bought a 30mm Superview since and surprisingly to me, on my scope, if I drop it all the way into the focuser, it wont achieve focus. To achieve focus I drop it in about 12mm then clamp it.
I can't get prime focus with my DSLR, a Canon 1000D, but it does focus if I use my cheap 2x Barlow/camera adapter.
http://www.ozscopes.com.au/skywatcher-2x-1-25-single-barlow-lens.html
Must get a good one some day!
Did you get just a T ring for your Canon or T ring plus something to screw it onto?
I found hooking my DSLR up to my scope a frustrating but educational experience!

Cheers

[Monstar]

Hey MW,

Congrats on the new scope after all this time, you've got a winner there!

Let us know how you get on.

[Mountain_Wanderer]

This is awesome!

I just took my scope outside for its first view of the night sky! Awesomeness.

I got Saturn in the low evening sky. Amazing!

The full moon was also a blast - it was so bright it blasted my eye out LOL.

Good times.

[rustigsmed]

Awesome work :thumbsup:

[astro_nutt]

Congrats on your new scope! I started off on a 200mm dob and has provided me with great views of the heavens.
Just a few tips which have been passed down to me.
Firstly, the base is made up from particleboard so a good idea is to smear some silicone over the exposed bits and allow to dry before assembly.
Give the base and outside of the optical tube a go over with some quality car wax.
Cheers!

[Pinwheel]

You now have that condition called "Aperturitus". It's only a matter of time until you need, must have, desire a bigger telescope.

Happened to me this year, It's caught by the "Bigger is better" virus..:lol:

Congratulations on you new Dob!

[astro_nutt]

''Aperturitus'' hit me late last year and I've been happier ever since!

[geolindon]

g day MW,
about 3 months ago i bought my 8" dob from a local member and am enjoying it heaps. the galaxies and nebulae thrill me and a highlight was recently watching (very faint but observable) comet 2013 A1 siding springs near the SMC.
i have dark skies tho tropical/humid.
i found that 2x barlowing my 9mm ep (133x to 266x) was usually beyond the atmospherics so when a 6mm (200x) came up i grabbed it and it now gets used most nights on both planets and DSOs :)
my 9mm 100fov gets the most use with the big fov meaning less nudging/moving the 'scope for more observing.
re lunar brightness; your OTA dust cap may have a removable section like a 50mm finderscope cap, try viewing luna with the dust cap on with only that 50mm section open.
enjoy!! L

[geolindon]

g day MW,
about 3 months ago i bought my 8" dob from a local member and am enjoying it heaps. the galaxies and nebulae thrill me and a highlight was recently watching (very faint but observable) comet 2013 A1 siding springs near the SMC.
i have dark skies tho tropical/humid.
i found that 2x barlowing my 9mm ep (133x to 266x) was usually beyond the atmospherics so when a 6mm (200x) came up i grabbed it and it now gets used most nights on both planets and DSOs :)
my 9mm 100fov gets the most use with the big fov meaning less nudging/moving the 'scope for more observing.
re lunar brightness; your OTA dust cap may have a removable section like a 50mm finderscope cap, try viewing luna with the dust cap on with only that 50mm section open.
enjoy!! L

[adi]

so did you make your DOB work with DSLR? are you able to capture images? as far as i know DOB's are not good when it comes to imaging. there is astrograph series for that. may be you could shed some light on this. i am also newbie in this area and considering to buy Dob or Astrograph. entry level are costing around 2000$. i hope i can make decent imaging setup within 1000$ to start with and i can add motor drive or make it go-to later stage.