Article: Part 2 - What's Wrong with each of my Scopes

[iceman]

Hi all.

Brian (Miaplacidus) has written a fantastic 2-part article for beginners.. this is the second part. It's well worth a read.

You can access the article from the Projects, Articles and DIY (http://www.iceinspace.com.au/?projects) section of the site, or directly from the link below:

Part Two: What's Wrong with each of my Scopes (http://www.iceinspace.com.au/index.php?id=63,261,0,0,1,0)

Thanks to Brian for writing such a comprehensive and complete article to help out the beginners.

[slice of heaven]

And again, Brilliant!!! :thumbsup:

[davidpretorius]

Again, fantastic!!!

[chunkylad]

What a great read!!! Ireally enjoyed both the content and the writing style. Congrats Brian;well done.

[Hitchhiker]

Parts I & II should be required reading for all beginners!

Well done, Brian.

[33South]

Great stuff, I could relate to the ETX105 bit.

[fringe_dweller]

I tips me hat, sir :thumbsup: :thumbsup: ...so in conclusion dobbies rule! (if you are on a budget) cant repeat that message too much methinks

[G00GS]

:2thumbs:

[rmcpb]

Read both articles. All I can say is thanx, I learnt heaps :)

[Miaplacidus]

Thanks for your positive comments, guys. (Now I'll just wait for the lawsuits to pour in.)

Seriously, reading over these articles again, I feel I was a bit harsh on both the ETX and the Megrez. I probably use the Megrez far more than any other scope at the moment. And I DO actually have a list of the SAOs of nearly every interesting double star south of declination +50 (I've even used an Excel scatter chart to turn it into a sort of star chart), so suddenly I find that the ETX has increased my potential observing opportunities to include even nights with a full moon. (Both these preferences probably reflect where I live. When you practise astronomy in cloudy Hobart, you have to maximize every opportunity you can!)

Anyway, guys, get stuck in. Aren't you all going to leap to the defence of your respective telescopes (and start denigrating all the others)? Else, where is the fun in writing the articles???!!!!

Cheers,

Brian.

[davidpretorius]

brian, how can it be attacked????

as you say, nothing is perfect, and yet most guys will not tell the noobie what is wrong with their scopes.

you have pointed out what is wrong. so unless you have made it up, then you can't be attacked.

if you had simply said a dob is best and left it at that, then "gloves are off".

but no, you have written a very very good article.

now all ou have to do is bring that to our little launceston get together.

actually, i am trying to organise a tassie IIS star camp in the next few years. I drove down the huon valley on business on tuesday, over to rokeby and then up thru cambridge. lots of nice dark sky sites. any tips??? from ross to campbelltown looked lovely and flat 360 degrees. Great lakes?????

[gaa_ian]

Brian, well done, Great article's lots of laughs, mixed with good advice for the beginner.

[bono]

Many thanks for the time taken to write this very useful article.

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.

thanks
Jono

[davidpretorius]

coming to melb to see bono and his mates late march!!

8" dob easy to carry!!! 6" even easier.

i would be interested to know what "too big" is for you?

[bono]

Actually a 6" DOB would be right in size. I am all for size and portability, durability, maintainability and versatility (terrestrial viewing?). I'm looking to nurture my beginner enthusiasm for now (quantity over quality I guess).

I'm having my sights set on the april fools concert David. Spent an unfruitful 2 hours trying to get arena tickets for the sydney ticks.

[davidpretorius]

6" or 8" dob gets ticks on:
size
portability
durability
maintainability

but for terrestrial viewing you would need a right angled finder which i think now comes with most dobs. mine does not so it the view is upside down and back the front.

also i would think a dob too close to the ground to be any good for terrestrial. a refractor on a tripod would be heaps better here!

as they say, have a look through them both and get it clear in your mind!

u2:
we spent 1 hour ringing and got tickets for melbourne, but with the damn comm games are on and accomodation in melb is sky high. got a mate in the city where i can crash!

[iceman]

bono, where abouts in Sydney are you?

Your best bet would be to come to one of our Sydney or Central Coast meetups and look through some telescopes yourself!

We're having one at Kulnura tomorrow night. Don't forget the Lostock AstroCamp in January as well, would be a great place for beginners to learn the ropes.

[iceman]

I don't think the last part is correct Dave.. that is, dobs rarely (if ever) come with right angle diagonal (I assume you mean diagonal instead of finder?).

Reflectors aren't really meant for terrestrial viewing, though of course they can be used that way if you like looking at upside down trees :)

[davidpretorius]

spot on mike, that is exactly what i meant, sorry bono

[Starkler]

I believe the size of the 6 and 8 inchers with respect to tube length and base size is the same for both, with the 6 being a little lighter. If cost isnt a concern go for the 8 if you decide on this type of scope.

[Miaplacidus]

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.

[Noidea]

Great article Brian, I enjoyed reading it.:thumbsup:


Cheers Paul!

[BLiTZWiNG]

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).

[Topher]

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

[erick]

In the eye. Try this, Chris:-

http://en.wikipedia.org/wiki/Eye_floater

[Topher]

Thanks erick

[Hagar]

:doh: 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.:hi: (love these litle critters)

[Topher]

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!:lol: 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

[i c with 1eye]

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:)

[Miaplacidus]

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.

[Blackant]

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 :lol:) 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 :eyepop::eyepop:

Kind regards

Ant

[Miaplacidus]

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.

[BLiTZWiNG]

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!

[Blackant]

The trick is to dress like a polar explorer. Beanie, thick polartec jacket and on occasions thermal underwear :lol:.

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 :thumbsup:

Regards

Ant

[Dunx.]

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!

[erick]

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 :)

[Dunx.]

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. :)

[StarGazing]

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. :question::question::question:

Clear skyes to all. Alex.

[that_guy]

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

[Miaplacidus]

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.

[that_guy]

Thanks Brian, great advice on the eyepiece and planet tracking. I hold off the eyepiece until I get more seriously into it..

thanks,
Tony

[magado]

I have a 8inch dob.It has been good to usebut of late there is no way I can
focus it It has been collimated it has a Crayford focuser. hoping for some
help.It looks like it wont be long until it goes to the tip
Magado

[AG Hybrid]

A very good essay. Ive been looking for a comprehensive guide like this to the basic pro's and cons of each telescope design in one article, comparing them to each other.

Nice one :)

[Miaplacidus]

I'm sorry to hear you're having difficulties with focusing. Hard to determine over the internet what might be wrong. Is there a club nearby that maybe you could take it to?

Otherwise, perhaps you could provide more details. What eyepieces are you using? How is the image distorted? (Perhaps using it during the day on some distant object on the horizon might provide some clues.)




Ta, Adrian.

[yusufcam]

i remember my first scope from not that long ago, i knew little about it when i purchased it but took the apparent honest advice of the salesperson (who in hindsight sold me exactly what i had unknowingly asked for).

After i bought it and returned home, i did some enthusiastic research on the web and was immediately dismayed to find a plethora of experts pleading grimly "whatever you do make sure someone doesn't sell you one of these things".

"Sheooot, i thought", what have i gotten into.

after several months of encountering such reports i succumbed and ended up getting the recommended beginner scope (the ubiquitious 8" dob, and further down the track, a 102mm F10 refractor). The moment i first used the dob i knew what the advantages of the original telescope, a short tube refractor, where (and coincidentally at the same time found the first astronomy book which sang the virtues of ST refractors, [Phillips Deep Sky])........

Even though i knew i prefer to buy food from a restuarant and take it home to eat. It didn't dawn on me that i would defer to a scope used in our backyard rather than a trek to a remote dark site, light pollution regardless.

Yes, Astronomy is conceptual, (yet, some objects are still beautiful) and that conceptualization extends to our telescopes....

One night (when i had only the ST) i noticed how forlorn i felt when i thought about the "blinding CA and puny magnification" of my ST achro. Then i stopped momentarily and thought what happens if i think about it as being like a set of powerful binoculars (wide field, light, portable), and instantly to my suprise felt absolutely great about them....


I have found that i love the hunt and my urban setting.

Once i've found where things are and are quite familiar with their locations i drag out the dob or F10 (on the balcony) and apply the magnification.

My scopes work as a team of sorts.....

So in the end it took all that time to find out it was right from the beginning (in this case).

Enjoy, why not...

Regards
Col ;)


to look at what each scope does best.

[barry2718]

Excellent advice in the posts here on equipment and pointing the Dob. I had encountered the Dob hole near Zenith and never thought to prop the scopes base on an angle. I have had a similar problem with my Eq mount 4" saxon and had to change to alt az tracking manual tracking near the South celestial pole, so it not just my lack of experience but real problem a design limitation of any scope. Great Articles wish I had found these sooner.

[chucho]

I am new in the use of a telescope, even though I have been reading about astronomy since long ago but nothing like get the real experience in your balcony.

Well I just need it to said thanks even if this was an old article this looks like a good push in the right direction.

[AlexD]

Very helpful - good to have a topic about what's "wrong" with various scopes, very helpful for the beginner!

[idlingdove]

Although written 14 years ago, I suspect this two-part article on scopes for beginners is just as relevant now as it was then.

Excellent advice and information! I learnt a lot. It's always good to hear viewpoints in forums like this one, where one can find an enthusiast's genuine opinion (as opposed to seller's hype and buyer's complaints)...:)

[ArnoldKMB]

Hey. I absolutely agree with you, these topics and comments have really helped me. So tnank you!:):):)