What 8" Dob to buy ? - Page 3

PCH (Paul) · #41 15-08-2008, 02:48 PM

Quote:

Originally Posted by NeilW

Hi all,

Do you know just what the "adjustable tension" on Andrew's new GSOs is or does, and is it useful?

Thanks

Neil

Hi Neil,

most brands of dobs have some way of implementing this. All it means is you can adjust the 'slackness' of a) the declination angle of the ota, and b) the effort needed to push the scope around in a circle on it's mount.

As an example, the more things you install at the focuser such as heavier eyepieces or a binoviewer (these are terrific

), you'll need to tighten up the declination setting a bit, or the focuser end of your new toy will just hit the deck -

. So yes it is very usefull !!

Hope this helps

NeilW · #42 15-08-2008, 03:13 PM

Thanks Paul, that's very helpful, and it's convinced me to wait a couple of months until Andrews get that model in...

UFO · #43 15-08-2008, 03:15 PM

Quote:

Originally Posted by PCH

Hi Neil,

most brands of dobs have some way of implementing this. All it means is you can adjust the 'slackness' of a) the declination angle of the ota, and b) the effort needed to push the scope around in a circle on it's mount.

As an example, the more things you install at the focuser such as heavier eyepieces or a binoviewer (these are terrific

), you'll need to tighten up the declination setting a bit, or the focuser end of your new toy will just hit the deck -

. So yes it is very usefull !!

Hope this helps

So it is nothing new. Even the old model has one?
I thought it had something to do with reflector adjustment.

And if you like to add red dot finder (designed for paintball rifles):
http://www.dealextreme.com/products.dx/category.910
http://www.dealextreme.com/products.dx/category.914

Fisherman (Mal) · #44 15-08-2008, 04:11 PM

Hi Guys,

Many thanks for all the info and 'the good oil' Eric.

Re The tube vertical and horizontal friction adjustment.

To my knowledge :

The 'GSO' has a spring either side of the tube that pulls it down and against some friction material thus stopping it flopping over...' all very techinical' but I guess it must work! (I beleive they've sold hundreds of them.)

Can someone varify this or have I missed somthing?

The new model (on its way!) has adjustable tension handles to acheive this.

The 'Skywatcher' uses two rotating handles, one either side of it tube mount to adjust this tension. Works well enough...I've tried it.

I can't understand why all of them were'nt designed like this in the first place !

Have a great weekend all -

Tomorrow is good day for fishing,

Mal

erick (Eric) · #45 15-08-2008, 06:00 PM

Quote:

Originally Posted by Fisherman

The 'GSO' has a spring either side of the tube that pulls it down and against some friction material thus stopping it flopping over...' all very techinical' but I guess it must work! (I beleive they've sold hundreds of them.)

Can someone varify this or have I missed somthing?

Mal, the GSO has two plastic trunions either side as the altitude bearings. They are a relatively smooth plastic. When in place, each sits on two small pieces of teflon, fixed to the base, against which they (and therefore the whole tube unit) can rotate so the tube moves in the altitude direction.

The two springs just pull the plastic and teflon harder together, thereby increasing the friction to try and stop an unbalanced tube unit (due to heavy eyepiece) from moving under its top-heavy weight - or vice-versa if a really light eyepiece.

One note, don't leave the finderscope off - its weight is expected to be found there in the design.

Fisherman (Mal) · #46 19-08-2008, 09:27 AM

Hi Erick,

But does it work or is it like so many things we purchase these days, ends up being modified to work as it really should have done in the first place?

A while ago I worked in the wholesale market place. Products we sold came and went. Quite a few times the model before the latest, the one we just sold out of or the one that was lasts years colour and no one now wanted was so much better than the new, you beaut 'priced right' one! When the market place realised that and the retailer stopped selling them we all looked forward to the next 'improved' one with the 'extra bits and pieces' Maybe, just maybe, they might forget how good that old model was and stop comparing !!

Mate, I dont want to get off the subject so tell me what you really think of that mechanism?

Mal

erick (Eric) · #47 19-08-2008, 10:01 AM

In that case Mal, you'd better buy an SDM or an Obsession.

I've had my hands on one or two GSO dobsonians of some age and possibly not great maintenance, and they were a horrible movement to my touch, particularly Az - far too much "stiction". Probably dust and muck got into the base. I move a new one in the showroom and it feels guite good. (But operation out in the cold/wet can be quite different to warm/dry of indoors.)

I preferred to improve mine. I'm a tinkerer. No problem for me that I take something I bought and make it better - I regularly do that. I like getting improved performance out of something I bought for a mediocre price by using a little bit if ingenuity, effort and a few parts.

Fisherman (Mal) · #48 19-08-2008, 11:16 AM

Hi Erick,

thanks for the reply.

As yet I dont know anything about those two scopes but I guess they're probably the 'Roll Royces' on the market and priced acordingly.

I don't mind tinkering myself. It's good fun but at times I've modified things to the extent that I should have really bought the 'other one' in the first place even though it was maybe 20% more expensive.

Mal

erick (Eric) · #49 19-08-2008, 11:32 AM

Yes, SDM - ballpark AUD7,700 for a 15"; Obsession - ballpark USD3295 for a 12.5" (plus shipping). That's what one would pay for very good quality movement in a dob - "off the shelf". That's a big difference compared with the Chinese 12" and 16" dobsonian scopes.

Fisherman (Mal) · #50 19-08-2008, 03:08 PM

Hi Erick,

I thought they would be pricey.
What about floating the base on a 'bath of mercury'.

Sounds weird I know, but I saw this on an antique many moons ago.
(I also beleive the stuffs poisonous so dont lick your fingers !) and where would you get it ?

I'll be happy with a Chinese one !

Mal

Brian W (Brian) · #51 19-08-2008, 10:56 PM

Being the very happy owner of a Meade 8" LightBridge I humbly suggest taking a look at one. Nothing against the others but why limit yourself to two options?
Brian

sikfish · #52 20-08-2008, 12:16 AM

Howdy,

I tried to get the 8" Skywatcher from BTOW who kept telling me it was coming and never did (after me chasing them up a number of times). Also the price they eventually offered was not compeditive. I ended up buying from York and it arrived in a week for $399 delivered and I am very happy. I think the whole thing about buying local is good - but only if the locals get their act together! Anyway just my opinion, it seems we need some competition here in WA.

Mike

Fisherman (Mal) · #53 20-08-2008, 09:14 AM

Hi Sikfish,

Sometimes the isolation of Perth gives the retailer a 'perceived' edge.

It does'nt work that way anymore does it.

From what I have gathered ( 'it may come with this or that, I dont really know' etc) it may not be easy dealing with China.

If you don't mind me asking..... what did you buy fromYork?

Mal

eze · #54 20-08-2008, 10:21 AM

Quote:

Originally Posted by sikfish

Howdy,

I ended up buying from York and it arrived in a week for $399 delivered and I am very happy.

Mike

Hi Mike
What do you end up buying from york? SkyWatcher Dobsonian - SW680 ? How did you get that price including delivery? On the website it is advertized as 499? What kind of focuser did it come with ? Did it include some eyepieces and fan ?

Cheers
Eze

Fisherman (Mal) · #55 20-08-2008, 04:10 PM

eze,

To my knowledge, the 8" 'Skywatcher' doesn't come with a fan?

The GSO does.

An 8" reflector for $399 sounds great.
Please let us know some details ie 'what, when and who" sikfish!

Thanks for your comment Brian W re the 8" Mead Lightbridge.

Must admit Ive not to have looked at that one.

Mal