ICEINSPACE
Most Read Articles
Moon Phase
CURRENT MOON Waxing Crescent
39.2%
The Sun Now
Time Zones
Sydney*
8:40 am
Perth
5:40 am
Auckland*
10:40 am
New York
4:40 pm
Paris
10:40 pm
GMT
9:40 pm




Go Back   IceInSpace > Beginners Start Here > Beginners Talk

Reply
 
Thread Tools Rating: Thread Rating: 8 votes, 3.63 average.
  #21  
Old 16-12-2005, 10:35 PM
Miaplacidus's Avatar
Miaplacidus (Brian)
He used to cut the grass.

Miaplacidus is offline
 
Join Date: Jul 2005
Location: Hobart
Posts: 1,227
Quote:
Originally Posted by bono

Can anyone suggest for me a $500 equivalent telescope (maybe from Andrews) to your 80 mm F6.25 (500 mm FL) short tube achromatic refractor (William Optics Megrez II SD) ?

I was about to get a DOB, but I see it is still a little too big for my liking.
Hi bono,

I'm not sure who to recommend for a refractor. I'd probably watch the buy and sell forum. There was a nice Nighthawk for sale there recently, and things like that come up every so often.

Naturally you've got to expect that a refractor isn't going to show you as much deep sky or even plantary stuff as a dob. The Wow-to-Sigh Ratio for a beginner is almost always highest with a dob (and usually by quite a margin). Still, a newt isn't for everyone, and nor is a dob. And Starkler is right: the weight and bulk advantage of a 6 inch dob over an 8 inch is hardly ever worth it when compared to the loss of aperture.

Anyway, happy hunting. (I still think about upgrading my Megrez, so if I'm going to sell it I'll let you know.)

Cheers,

Brian.
Reply With Quote
  #22  
Old 18-01-2006, 10:02 PM
Noidea's Avatar
Noidea
Keen Newbie

Noidea is offline
 
Join Date: Jan 2006
Location: Castle Hill, Sydney
Posts: 48
Thanks for the article

Great article Brian, I enjoyed reading it.


Cheers Paul!
Reply With Quote
  #23  
Old 09-01-2007, 02:49 PM
BLiTZWiNG (Trent)
Certified n00b

BLiTZWiNG is offline
 
Join Date: Jan 2005
Location: Beachmere, QLD
Posts: 277
I just read it. Great article. I'm definitely considering buying a smaller scope than my 8" GSO dob for transporting around. (ie this McNaught comet, the west side of my house is obscured by a hill, houses and very tall gums). I also want something that allows me to track planets a little easier. When I bought the dob I wanted to look at everything, and I still do. As an amatuer amatuer, I don't think dobs are very good for planet tracking. If you do get a planet lined up though, they sure look great!

I do however have to wonder what secrets the above posters are hiding with respect to comfortably moving an 8" dob! All throughout the article the mantra of trying to keep the beginner interested is repeated, but if you imply to a beginner that carting around an 8" dob is as simple as carrying around a laptop, baby jesus is gonna whine like a ... baby. Sure some people will get over it quick, but I didn't. My scope has sat unused in the corner of my office for the last 2 years because its such a pain to move. Every time I think of using it, baby jesus cries and the sigh factor comes into play.

I never bothered trying to stick it in the car, Im pretty sure it wont fit, and I'm scared that it will get damaged because I don't have any kind of case to put it in (yes I still have the foam it came in, and no I haven't built a case for it using the foam because I suck at building stuff and I'm good at accidentally breaking stuff).
Reply With Quote
  #24  
Old 07-08-2007, 09:45 AM
Topher's Avatar
Topher
Stargazer since breakfast

Topher is offline
 
Join Date: Aug 2007
Location: Canberra
Posts: 19
Help with Terminology

Hi all,

Just need some help with terminology. I have checked out Iceman's Glossary of Terms (by the way, thanks for that Iceman) but it doesn't have the term I am after.

I am refering to Part 2 of Brian's article on first telescopes. In the Bino section he refers to
"Also, if you have a lot of floaters, binocular viewing is a godsend." What is a floater?

Hope someone can help!

Chris
Reply With Quote
  #25  
Old 07-08-2007, 10:32 AM
erick's Avatar
erick (Eric)
Starcatcher

erick is offline
 
Join Date: Dec 2006
Location: Haifa, Israel
Posts: 8,439
Quote:
Originally Posted by Topher View Post
........What is a floater?

Hope someone can help!

Chris

In the eye. Try this, Chris:-

http://en.wikipedia.org/wiki/Eye_floater
Reply With Quote
  #26  
Old 07-08-2007, 10:41 AM
Topher's Avatar
Topher
Stargazer since breakfast

Topher is offline
 
Join Date: Aug 2007
Location: Canberra
Posts: 19
Thanks erick
Reply With Quote
  #27  
Old 08-08-2007, 09:07 PM
Hagar (Doug)
Registered User

Hagar is offline
 
Join Date: Oct 2006
Location: Australia
Posts: 4,645
Sad But True

Great article that I can relate to. The scopes were a little larger in my case but the end result is somewhat similar.
An ED80 from Skywatcher (love this little scope) and an 8" SCT. Both mounted happilly on an HEQ5 goto mount. They allow me to take happy snaps and also great visuals as well. I wish you had written this article a couple of years back before I made a significant down payment on Bintel's business and a significant increase in Ebays funding.
I am now very satisfied but have a wife who just doesn't understand the ways of the universe, at least when compared to our bank account.

Really great articles. (love these litle critters)
Reply With Quote
  #28  
Old 13-08-2007, 10:05 AM
Topher's Avatar
Topher
Stargazer since breakfast

Topher is offline
 
Join Date: Aug 2007
Location: Canberra
Posts: 19
With Much Appreciation

I really have to say that this thread (and and the Part 1 thread as well) have been most helpful.

As I am sure you are all aware, this hobby is not simple or complex, just simply complex. But with people such as Brian, who have been there and done that, making all (more correctly most, eh.. some) mistakes for me, it does make what could be a complex issue almost an everyday occurance.

I now feel confident that I can now go out and window shop for a telescope that will suit me just perfect! Seriously, I am not daunted by the prospect of buying a telescope for the first time, thanks to this thread and it's companion. Now if there was only a way for me to control my urge to buy the Rolls Royce instead of a Toyota, I would be a happy chappy.

Thanks Brian for an informative article!

Chris
Reply With Quote
  #29  
Old 26-12-2007, 08:41 PM
i c with 1eye's Avatar
i c with 1eye (Rob)
OMG! Its full of stars.

i c with 1eye is offline
 
Join Date: Dec 2007
Location: Sydney
Posts: 8
You have been unfair to the megrez, as I have one of the older J and G optics one, 480mm x 80mm f6 sd. I found that the choice of eyepiece will give a
blue fringe to the moon
Reply With Quote
  #30  
Old 26-12-2007, 10:29 PM
Miaplacidus's Avatar
Miaplacidus (Brian)
He used to cut the grass.

Miaplacidus is offline
 
Join Date: Jul 2005
Location: Hobart
Posts: 1,227
Quote:
Originally Posted by i c with 1eye View Post
You have been unfair to the megrez, as I have one of the older J and G optics one, 480mm x 80mm f6 sd. I found that the choice of eyepiece will give a
blue fringe to the moon
Indubitably unfair, as you say. Mea culpa. A great little scope, which I used a lot.

Still, having upgraded to the F6.9 fluorite doublet the improvement in chromatic aberration is striking nonetheless, and I see that William Optics ended up including a fringe killer filter in their package, so I guess sufficient numbers of people thought it was annoying enough to prompt the change. But CA is one of those things that troubles some people more than others. What can I say? YMMV, perhaps?

All the best, and have a cool Yule.

Regards,

Brian.
Reply With Quote
  #31  
Old 22-08-2009, 08:52 PM
Blackant's Avatar
Blackant (Ant)
Tassie Telescope Gnome

Blackant is offline
 
Join Date: Jun 2009
Location: Tasmania
Posts: 64
Thumbs up

Hi Brian,

I just wanted to say thanks for the two beginner telescope articles, they've really helped me choose my first telescope. I've fallen in and out of love with astronomy since I was a kid, and I've spent most of my time using binoculars.

A while ago I inherited a 114mm Skyrover on an equatorial mount off my uncle (he didn't like it either ) and what I though was good fortune actually nearly turned me off the whole hobby.

For me the sigh factor was huge, and I ended up putting it in the roof space and going back to using my binoculars. After reading your article, and getting a good tax return, it inspired me to give a telescope another go.

Not surprisingly it's an 8" Dobsonian from Bintel, and it is perfect for me. My mates call me Ant for a reason; I'm 165 cm tall and weigh 60 kilograms. I have no trouble carrying it in two trips over the child safety gate in the spare room, past kids, dogs and down the stairs to my backyard. With the fan it takes next to no time to cool down, and when the lens caps come off, the glorious sites that it reveals in my dark Huon Valley skies is truly awe inspiring

Kind regards

Ant
Reply With Quote
  #32  
Old 23-08-2009, 08:55 AM
Miaplacidus's Avatar
Miaplacidus (Brian)
He used to cut the grass.

Miaplacidus is offline
 
Join Date: Jul 2005
Location: Hobart
Posts: 1,227
Congrats, Ant. I feel confident you'll enjoy the scope. You've got lovely dark skies in the Huon. Almost criminal not to have a telescope there.
Cheers,
Brian.
Reply With Quote
  #33  
Old 23-08-2009, 09:50 AM
BLiTZWiNG (Trent)
Certified n00b

BLiTZWiNG is offline
 
Join Date: Jan 2005
Location: Beachmere, QLD
Posts: 277
I'm impressed that you're able to go outside at night in Tasmania! I was a Victorian when I wrote the post above, and it was cold enough there to stop me staying outside for long!
Reply With Quote
  #34  
Old 23-08-2009, 05:27 PM
Blackant's Avatar
Blackant (Ant)
Tassie Telescope Gnome

Blackant is offline
 
Join Date: Jun 2009
Location: Tasmania
Posts: 64
Quote:
Originally Posted by BLiTZWiNG View Post
I'm impressed that you're able to go outside at night in Tasmania! I was a Victorian when I wrote the post above, and it was cold enough there to stop me staying outside for long!
The trick is to dress like a polar explorer. Beanie, thick polartec jacket and on occasions thermal underwear .

The other night I staggered inside after a couple of hours so bundled up that my own dog didn't recognize me. At least I know she's a good guard dog now, unfortunately she woke the whole house up barking and bailing me up into a corner, she didn't calm down till I put my denver chair down, took off my beanie and jacket

Regards

Ant
Reply With Quote
  #35  
Old 17-09-2009, 03:00 PM
Dunx. (Duncan)
Registered User

Dunx. is offline
 
Join Date: Sep 2009
Location: Glen Alpine
Posts: 14
Hello Everyone!

My first post.. I'll start off by saying thank you already for the extensive wealth of information I have been provided with from this forum.

I'll be purchasing an 8" dob very soon and I have a question related from something Brian stated in his article.

Why do dobs have problems looking into the zenith? I would have assumed that given the design of the OTS and the nature of the dob mount it would have no problem pointing directly up.

Can anyone please explain to me why this is a problem?

Thank you!

Edit: I also forgot to add that I read both articles and think they are brilliant thank you for the posts Brian!

Last edited by Dunx.; 17-09-2009 at 03:05 PM. Reason: Recognition
Reply With Quote
  #36  
Old 17-09-2009, 03:28 PM
erick's Avatar
erick (Eric)
Starcatcher

erick is offline
 
Join Date: Dec 2006
Location: Haifa, Israel
Posts: 8,439
Hi Duncan

You are right, They have no trouble pointing to the zenith or close. The problem is moving them in the azimuth direction when you have them pointing there! When the scope is at low elevation, you just push away from you or pull towards you to move in azimuth. When it is pointing almost vertically, you lose your mechanical advantage of the OTA as a "lever" in the azimuth direction. Tracking an object at the zenith, as the earth turns beneath your feet, can be difficult at first.

This is called the infamous "dob hole".

Three solutions:-

1. Lazy way - Go and have a long cup of coffee until the object of interest moves 10-15 deg past the zenith

2. Unsophisticated way - Prop up one side of the ground board with, say, a brick. Now the real zenith is no longer in the scope's "dob hole". Remove the brick when done with the zenith.

3. Sophisticated way - Moving in the azimuth direction means rotating the scope around its vertical axis. When the OTA is almost vertical, using it as a lever doesn't work any more - you cannot push/pull, you have to rotate it. Keep your left hand on the top of the OTA to move in altitude direction and reach down with you right hand and grab one edge of the base and rotate the base to the left or right to get the azimuth movement. I find that on an 8" GSO with a smooth movement (Ebony Star laminate fitted) there was plenty of mechanical advantage at the edge of the base to move the scope smoothly in azimuth. On the 12", if I wanted to keep my eye at the eyepiece, I think I struggle to reach the base - but I had other bits sticking up that were connected to the base that I could grab hold of and use to rotate the base.

Yours in "dob-hood"
Eric
Reply With Quote
  #37  
Old 17-09-2009, 05:12 PM
Dunx. (Duncan)
Registered User

Dunx. is offline
 
Join Date: Sep 2009
Location: Glen Alpine
Posts: 14
Quote:
Originally Posted by erick View Post
Hi Duncan

You are right, They have no trouble pointing to the zenith or close. The problem is moving them in the azimuth direction when you have them pointing there! When the scope is at low elevation, you just push away from you or pull towards you to move in azimuth. When it is pointing almost vertically, you lose your mechanical advantage of the OTA as a "lever" in the azimuth direction. Tracking an object at the zenith, as the earth turns beneath your feet, can be difficult at first.

This is called the infamous "dob hole".

Three solutions:-

1. Lazy way - Go and have a long cup of coffee until the object of interest moves 10-15 deg past the zenith

2. Unsophisticated way - Prop up one side of the ground board with, say, a brick. Now the real zenith is no longer in the scope's "dob hole". Remove the brick when done with the zenith.

3. Sophisticated way - Moving in the azimuth direction means rotating the scope around its vertical axis. When the OTA is almost vertical, using it as a lever doesn't work any more - you cannot push/pull, you have to rotate it. Keep your left hand on the top of the OTA to move in altitude direction and reach down with you right hand and grab one edge of the base and rotate the base to the left or right to get the azimuth movement. I find that on an 8" GSO with a smooth movement (Ebony Star laminate fitted) there was plenty of mechanical advantage at the edge of the base to move the scope smoothly in azimuth. On the 12", if I wanted to keep my eye at the eyepiece, I think I struggle to reach the base - but I had other bits sticking up that were connected to the base that I could grab hold of and use to rotate the base.

Yours in "dob-hood"
Eric
Ahhh, Thanks erick.

After giving it some thought, I assumed it might have something to do with the maneuverability of the tube in all different directions when it's upright. Thanks for shedding light on that, I was fearing it couldn't point upright for a reason like it's mount only allowed it to swing 80 degrees, not the full 90.

Thanks again.
Reply With Quote
  #38  
Old 02-10-2009, 08:39 PM
StarGazing (Alex)
Registered User

StarGazing is offline
 
Join Date: Sep 2009
Location: Melbourne, Australia
Posts: 163
Great reading for the novice ......... wish I had this info when I started out a year ago. But like he said the dob is a great starter. Good reconmedation for any one looking into astronomy first up. Its a minefield of marketing that gets us so confused at times.

Clear skyes to all. Alex.
Reply With Quote
  #39  
Old 17-12-2009, 03:28 PM
that_guy (Tony)
Local Korean Millennial

that_guy is offline
 
Join Date: Dec 2009
Location: Gold Coast
Posts: 1,639
Just read the articles, all wonderful and real helpful advice for the noobiest noob around such as my self... If I do buy a 6" dob, then what eye piece should i get with it? and how do track planets with a dob. even though its not recommended?

Thanks,
Tony
Reply With Quote
  #40  
Old 17-12-2009, 05:31 PM
Miaplacidus's Avatar
Miaplacidus (Brian)
He used to cut the grass.

Miaplacidus is offline
 
Join Date: Jul 2005
Location: Hobart
Posts: 1,227
Quote:
Originally Posted by that_guy View Post
Just read the articles, all wonderful and real helpful advice for the noobiest noob around such as my self... If I do buy a 6" dob, then what eye piece should i get with it? and how do track planets with a dob. even though its not recommended?

Thanks,
Tony
Hi Tony,
I think most new dobs nowadays come with a couple of plossl type eyepieces, often appropriately around the 25 mm and 10 mm focal length. These are usually of sufficient quality to give decent enough views. So you really should get started with them before thinking of outlaying a fortune on fancy glass. (I certainly ended up with too many eyepieces, which is a common trap for beginners, owning I'm sure at one point what seemed like one of every imaginable focal length. Since then I've systematically reduced them to, guess what, 30 mm, 10 mm, and a rarely used 5 mm.)

The magnification you will obtain will depend on the focal length of the telescope. Divide the focal length of the telescope by the focal length of the eyepiece, and that is how many times the object is magnified. (You probably already know that.)

People also talk about exit pupil, which is the size of the disk of light that comes out of the eyelens of the eyepiece. I think you can calculate this by dividing the focal ratio of the telescope (which equals focal length of the telescope / aperture) by the focal length of eyepiece (in mm). They say if an eyepiece has an exit pupil bigger than the size of your own pupil (5-7 mm, depending on whether you're old or young, have dark irises or pale), then you are wasting light. This is a technical thing which I strongly suspect was invented to bamboozle beginners and is quite unnecessary for most of us to worry about, especially early on. (Mind you, if the exit pupil is too small, it can be a bit awkward to see properly, and you're more likely to see annoying artifacts like "floaters" and other junk that float about in your eyeball.)

Higher magnification (if the sky's steadiness allows) is preferred if you want to see detail on planets, so the 10 mm eyepiece is for that. Honestly, unless you live in an exceptional climate, shorter focal length eyepieces seldom get much use.

I never meant to imply that it is not recommended to track planets with a dob. As I'm sure you know, all celestial objects will appear to move when viewed through a telescope because of the earth's rotation, and you have to compensate for this by constantly moving the telescope. This is true of all telescopes that don't have a motor drive. You just have to nudge the dob each time the planet is drifting to the edge of the field of view, but it isn't a big deal and is something that is quickly learned.

Welcome aboard, and I hope you enjoy the views.

Merry Christmas, too.

Brian.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 07:40 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Advertisement
OzScopes Authorised Dealer
Advertisement
SkyWatcher 2018 Catalogue
Advertisement
Bintel
Advertisement
FLI Cameras and Imaging Accessories
Advertisement
NexDome Observatories
Advertisement
SkyWatcher Esprit
Advertisement
SkyWatcher WiFi Adaptor
Advertisement
Atik 16200
Advertisement
Lunatico Astronomical
Advertisement
Astronomy and Electronics Centre
Advertisement