8" VS 10" Dobsonian

[DRCORTEX (Lance)]

Hi People,

I've been reading, and reading, and reading for a few weeks now, weeding out those scopes which are simply trash ( Ebay ), or out of my league right now ( Meades with Goto's ).

Basically, as many people have put it "I get my best bang for buck with one of these 8 or 10 Guan Shengs.

As people have already said, the Guan Sheng models look like great value for the money, so that is where I am headed. Andrews is only 15 minutes from my place.

Now to the questions, assuming I do go ahead and purchase a telescope ( I've been using binos for a month or so )

a) Will I be able to either replace my mount with a computerised version later, or upgrade the mount itself ? I would like to take a shot at astrophotography one day

b) Should I purchase a collimator when I purchase the scope, and should it be a cheshire or laser version ?

c) Which way do I go - 8 or 10" - is there really that much more light gathering power in comparison to the price ?

d) Is what I get with my first purchase sufficient - should I look at an extra eyepiece or two ? and what about a barlow ?

e) I wear glasses and suffer from astigmatism - could this be a problem ?

f) Could someone give me the dimensions and wieght for the 8 and 10" models - I need to determine whether I could fit them in my little Hyundai Accent ( fortunately the back seats fold down ). Can the scope be easily damaged by repeated trips in a vehicle ?

g) The binos I use arn't really that crash, they cost me some $65 and are 50X7's - with all the light pollution, they give an ok view of the moon, and I can definitely get some colour resolution from Mars and Saturn, plus can make out some nebulae. How much more would I actually be able to view from an 8 or 10". Would the light pollution living with so many street lights, etc, make viewing from home not worth the effort ?.

Anyway, thats about it for now. Hope I havn't simply bored you all totears with the same questions that other newbies ask.

Regards,

Neo ( As in Neo Cortex - not the one from the Matrix )

[hogly52 (Graeme)]

Hi and Neo, ,

You've come to the right place to have all your questions answered and I know there are the people here who will answer them all for you. Some I could answer myself, but I'll leave it to the more knowledgeable IIS members.

Good to see you on board, I'm sure you'll learn a lot while here.


Graeme

[Striker (Tony)]

10"....just for the fact your not bending over as much....not good for the back.

[iceman (Mike)]

HI Neo!

Welcome to the forum! How did you hear about us?

Great to see you've done your research.. i'll answer a few questions now and i'm sure others will provide more answers.

a) Yes and yes. You can buy an EQ6 or similar motorised/computerised mount (looking at $1500+) and put the newtonian OTA on it for tracking and astrophotography. For simple tracking and simple astrophotography, you can also use an EQ platform while still keeping the convenience of a dobsonian base.

b) Yes, definitely. Get the cheshire/sight tube combo. But you can also simply use a film cannister with a small hole drilled in it.

c) Aperture wins, always. The 10" is worth the extra.

d) The eyepieces that come with the scope will get you buy, but it won't be long before you'll want some extra eyepieces (better quality ones) and also a 2x barlow. Budget at least $500 for eyepiece/barlow upgrades in the next few months.

e) No, it's no problem. But if you need glasses to observe then your eyepiece choices mean factoring eye relief as a higher priority. You'll need eyepieces with more eye relief so that they are comfortable to use and you can see the whole FOV while wearing glasses.

f) I think they're on the GSO website, someone else will provide a link. The scope won't get damaged by transportation as long as you secure it properly (don't let it roll about the back ). But collimation can be knocked out in the car, so you will need to learn to collimate and check it regularly.

g) The binos will still get some use occassionally - they'll be fine in combination with your scope. And even in light polluted skies you will see a MAJOR (and I mean, major!) difference between the binos and a 10" scope. Binos are great for widefield scanning of the milky way, but they just don't compare to what you'll see on planets, the moon and deep space objects through a 10" telescope.

I'd also recommend getting to a local observing group and looking through some similar telescopes before taking the plunge. You'll get a much better feel for what you're getting, and what you'll be able to see.

Also, it would be great if you could come to IISAC at the end of the month - there'll be tonnes of people to help you spend some money and loads of telescopes to look through.

Good luck and keep asking questions!

[Truscott]

I have heard of Andrews on this forum before, who, what and where is he ?? P.S Love the smiliely options!

[acropolite (Phil)]

Welcome Neo,
ditto what mike said, basically there's no substitute for aperture and the GS dobs certainly represent the most bangs for your buck on offer. Regarding astigmatism, one eyepiece manufacturer, Televue, offers correction lenses for some of their eyepieces. TV eyepieces (and products in general) don't come cheap but are excellent quality. Here's a link to the televue site describing the DIOPTRX™ eyepieces. http://www.televue.com/engine/page.asp?ID=259 If you have the money it would be well worth going for quality eyepieces right from the beginning as you will find after a very short period of time that eyepiece selection is of primary importance.

[ballaratdragons (Ken)]

Originally Posted by Truscott

I have heard of Andrews on this forum before, who, what and where is he ??

Andrews are at www.andrewscom.com.au.
They are mainly a Ham Radio enthusiast store but he bulk orders telescopes and binoculars so he can give a better price than the usual telescope shops. They are not really into 'pre-sale' preparation. You get it in the box it left Taiwan in. But the prices are good.

I have only heard of one scope that didn't turn up as ordered. It had mirror damage.

Originally Posted by DRCORTEX

f) Could someone give me the dimensions and wieght for the 8 and 10" models - I need to determine whether I could fit them in my little Hyundai Accent ( fortunately the back seats fold down ).

Yep! Here is the site with all the dimensions, weights etc of ALL the GS Models. Hope it helps. Just scroll down to the size you want to know about. http://www.telescope-service.com/dob...iansstart.html

And if you can't afford, or transport, the 12" go the 10". Size does make a big difference. There is quite a big difference in Mirror area between an 8" and 10".

And yes, you will see an amazing difference between binoculars and a 10" Dob!!!!

I have recently placed my 12" Dob onto an EQ mount with Tracking. Buying a Dob doesn't mean you are stuck with using it as a Dob. Good luck Neo.

[mickoking]

G'day Neo,


You'll be on a winner with a 250mm Dob. Thousands of deep sky (and solar system) object's will be visible many showing breathtaking detail. As for eyepieces get the best you can resonably affoard. Also I personally dont rate barlows its just more glass between the object and your eye and are a bit awkward to use with an un-driven Dob.

I hope I have been of help

[ballaratdragons (Ken)]

Oh, and another thing Neo, make sure when you order your scope get the one with the 'Crayford Focuser'. It is about $100 extra (I think) but most definately worth it!!!!

[jjjnettie (Jeanette)]

Hi Neo,
I've got astigmatism as well and find my 2" GSO eye piece that came with my scope
( a 10" dob from Andrews ) most comfortable to use when wearing glasses. Otherwise I take them off to look through the 1 1/4 ".

[Reg Johnson]

Hello, Ive recently bought a 12" dob and im just beginning to realise that I should have bought better eypieces to start with (instead of the generic ones supplied) it has great light grasp at 60x and 100x but on planets can only just hang in there at 166x but nearly useless at 375x (I thought I needed high power for planets) this at 2am , so the sky was dark
enough, Ive never seen any detail at all on Mars which was disapointing , and am reluctant to spend
$250 - $350 on an eyepiece that might show detail.

[janoskiss (Steve H)]

As an 8" owner for the past 12 months I can wholeheartedly recommend you get the 10", which is the max aperture in this design that is still comfortably transportable in a sedan or hatchback.

[mickoking]

Originally Posted by Reg Johnson

Hello, Ive recently bought a 12" dob and im just beginning to realise that I should have bought better eypieces to start with (instead of the generic ones supplied) it has great light grasp at 60x and 100x but on planets can only just hang in there at 166x but nearly useless at 375x (I thought I needed high power for planets) this at 2am , so the sky was dark
enough, Ive never seen any detail at all on Mars which was disapointing , and am reluctant to spend
$250 - $350 on an eyepiece that might show detail.

Could be the tube currents ruining your view of the planets at higher magnification. I very rarely get good high magnification views thru my 250mm Dob even though it has a theoretical max magnification of x500.

[Reg Johnson]

Thanks mickoking , it actually was very windy so it could have been the problem. also ive been looking at some of the reviews , and one that interested me was on the series 500 plossel......use it as a door stop.

I'm going to save my pennies.

Thanks for the reply

[iceman (Mike)]

Reg,

Due to seeing conditions, transparency, thermal currents in your tube and not having your mirror at ambient temperature, it's actually very rare that you'll use an eyepiece that gives you magnifications of 200x or over.

It's not so much the type of eyepiece (series 500 or a nagler) that limit your view of detail on the planets, it's those factors described above that are the major influence.

In my 10" dob, my main planetary eyepiece will be (soon to be purchased) a 6 or 7mm eyepiece, which will give me 208x on steady nights. When the seeing is not good, I can only use a 9mm, which only gives me 138x.

On above average nights, I'll be hoping to use a 5mm which will give me 250x. So you can see that it's just not possible to use high magnification on the planets 99 nights out of 100.

So while a better eyepiece will help you see detail when the seeing is good (better contrast, light transmission, colour reproduction, edge performance), don't try and push the magnification too high, as all you'll get is a wobbly blurry bubble.

Also don't forget that Mars is shrinking fast, less than 11" now and it's very difficult to see detail on something so small. You should try Saturn, rising around midnight and high enough to view by around 2am. On a steady night you'll see the cassini division almost all the way around, banding on the globe, it's an awesome sight.

And don't forget our nearest neighbour, the moon! Plenty of fine detail to see on the moon and can be observed at different times throughout the month so it's always convenient (except at full moon!)

Hope i've helped!

[davidpretorius]

Originally Posted by Reg Johnson

was on the series 500 plossel......use it as a door stop.

i also remember at the november star camp, ken said he hardly ever used his 6.5mm eyepiece in his 12" which gives him 230x. We chucked it in his scope anyway and due to the major factors ie mirror the same temp as ambient and the seeing was 9/10, then out popped the cassini division and 5 or 6 moons of saturn from memory.

Do not confuse external factors with poor optics. I have mainly series 500 and have been using for 6 months. I am now moving on up, but I believe I will always class them as "good", it is just that i am ready for "better" r "best"

The series 500 are fine as a beginner's eyepiece. It is just that for the higher powers 6.5mm to 12mm, you need a cooled mirror (<1 degree difference) and good to great seeing.

I have a 5mm vixen at the moment ( aprox $200) and it also will not work well if the conditions are not right!

[davidpretorius]

Hi Neo!

as the guys have said, go the highest diameter you can afford, carry and transport.

I have a 10" dob and have just bought a dob driver, so it is now computerized. So i have tracking and "goto". Very easy to install for me and enjoyed the project.

I also believe i will get a heavy duty EQ mount down the track.

So yes, it is a very versatile telescope.

The eyepieces will be fine to start with, but the 6.5mm if you get that will be very vard to look thru with glasses. The vixen range look very promising as they have lovely eye relief and if you are looking at higher power eyepieces (ie <12mm), i would recommend them

[DRCORTEX (Lance)]

Hi People,

Thanks for the info. Gives me that bit more info I need before my purchase. I think I'll hold out another month and attend one night of the upcoming viewing camp, to serve as a further buying guide. I'm sure there will be a few people there with both the telescopes I am looking at, and you never know, I may bite the bullet, and crash the credit card for something better if I see it.

In the meantime, I'll take a look at the forum re the viewing camp for details of where, when and how much.

Regards,

Neo ( Lance )

[janoskiss (Steve H)]

Make sure the mirror's got a cooling fan. Makes a big difference in how high a magnification the scope will support; even on my 8" Dob. 200x is usually not a problem and more often than not I go well over that from suburban back yard. At 1200m+ altitude I can consistently get 300x or more out of the scope. Before I fitted the fan I could rarely go over 150x. Jupiter and Saturn look amazing at high magnifications.

[ving (David)]

Originally Posted by Reg Johnson

Thanks mickoking , it actually was very windy so it could have been the problem. also ive been looking at some of the reviews , and one that interested me was on the series 500 plossel......use it as a door stop.

I'm going to save my pennies.

Thanks for the reply

actually it depends on seeing. I have a 6.5mm series 500 EP and during good seeing I have seen plenty of detail on planets.

Neo: I have a gso 8" which i have mounted on a EQ. I kept the round thingies on the side of the optical tube so i could mount it back on the dob base to... makes it all very versatile
heres a link to a pic.
http://img.photobucket.com/albums/v4...attachment.jpg
it all comes down to what your budget is tho. if you can aford a 10" with all the bits and pieces you need to go along with it then et that, if not then you may have to go down a size
when i bought my 8" it was the price of the current 10"

but either the 8" or 10" will let ou see heaps when the seeing is good

another alternative is the gs660 eq mounted 8" on the andrews site. or maybe you want a refractor? i'd go a short tube one from AOE on an eq mount... aoe.com.au