Message Font: Serif | Sans-Serif
 
UnThreaded | Threaded | Whole Thread (11) | Ignore Thread Prev Thread | Next Thread
Author: TMFOrangeblood Big gold star, 5000 posts Old School Fool CAPS All Star Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: of 1797  
Subject: Telescope talk Date: 2/6/2002 9:19 PM
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 1
jiml8 said: My wife teaches astronomy at an area university, and we have the school's 9 inch reflector set up in our house.

With the new blood in here from Selena's post, this seems a great time to get some advice on a couple of telescopes I'm considering. Below is the text of an email exchange I had with someone who just bought an Orion SkyQuest™ XT8 Dobsonian Reflector:
http://www.telescope.com/cgi-bin/OrionTel.storefront/3c61000700870bd2272180f272880630/Product/View/A302

...but it hasn't been delivered to him yet. If you're interested in this kind of stuff, please read on and feel free to reply with any help. Thanks!


=========
Him - I recently purchased such a scope from Orion Telescopes and Binoculars (www.oriontel.com) based on the recommendation of Ed Ting of www.scopereviews.com and the Sky and Telescope review (http://www.skypub.com/resources/testreports/telescopes/0001sixdobs.html) that rated it best in its category.

Me - I, too, am considering the very telescope you purchased. However, I think I'm leaning toward spending $40 more and buying the Orion SkyView Deluxe 8" EQ Newtonian:
http://www.telescope.com/cgi-bin/OrionTel.storefront/3c5dfe41052b1d92271d80f2728806b4/Product/View/A319

For the extra $40, I would get an 8" scope with an equatorial mount... and I could throw in another $35 and get the AccuTrack Electronic Drive for the mount... which would allow me to do some limited astrophotography, I think. However, I have the following concerns:

1. The SkyView is f/4, compared to your SkyQuest's f/5.9. I know that gives the SkyView a wider field of view (and better for deep sky objects)... but I read in a book that the faster f-ratios aren't as good for planet-viewing as the slower f-ratios, and I can't quite understand why. Also, the book said faster f-ratios (especially under f/6) are far more likely to suffer from comas and will likely need re-collimating every session. Do you have a grasp on any of this, especially the advantages/disadvantages of f/4 vs. f/6?

2. While I am a fairly experienced photographer... I know nothing about astrophotography. For all I know, I'll get the SkyView and find out I really can't take decent pictures after all. I'm only looking to be able to take photos occasionally, and it needn't be anything fancy. But I'd like to know if the SkyView can handle that, even though the web page indicates it can handle some simple photography. (I know the SkyQuest cannot handle astrophotography because of the Dob mount.)

3. I don't understand the shipping charges on the page I linked above. It shows 2nd day shipping for the "reflector" at $100, plus $45 for the tube assembly, plus $20 for an oversize charge! Do we have slower shipping option? I see your scope was supposed to cost $120 2nd day.... plus a $30 oversize charge? Yikes! Are there no Orion dealers around the country? I don't think I'd be able to bring myself to pay $165 for shipping.


Him - I have been reading about scopes for a couple of months now, but I am still a beginner, so please take what I have written below with a large grain of salt. Also, I know nothing about photography and even less about astrophotography.

I myself was considering the equatorial version of the 8" scope, but the impression that I have of the mount is that is not very good for larger loads. My concern was that it would be shaky - which is a real problem visually and worse yet for astrophotography.

Planetary viewing and photography require high magnifications to allow for an image size large enough to display details. A given eyepiece will yield higher magnifications with higher focal ratio scopes. High magnification in a low f/ratio scope may require a Barlow lens, which causes a dimming of the image. As the f/ratio decreases, the curvature of the mirror increases, which causes increased coma. This increased coma is evident in a larger portion of the field of view. Also, low f/ratio scopes are less tolerant of miscollimation and may be more difficult to collimate. After a scope has been set up properly, there is really no visual difference between different f/ratios, except for the coma. Photographically, the camera would probably affect the f/ratio of the total camera/scope system.

The Sky View mount may be unsuitable for long exposure photography, but may be adequate for short exposure shots of the planets. Also, while the Dob cannot track for long exposure shots, you may be able to take very short exposure shots (a couple seconds).

I myself do not understand the shipping charges, but if you are not in a real hurry for your scope don't worry about the 2nd day option. My scope was shipped to Miami via FedEx ground and arrived five business days after the shipping date. The total shipping cost, inclusive of the oversize charge, was approximately $50.00. This standard shipping option was available for selection during the ordering process.

I have not yet received my scope as it has to be shipped from Miami to me. I will be sure to let you know how it works out.


Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Print the post Back To Top
Author: Messier101 One star, 50 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 145 of 1797
Subject: Re: Telescope talk Date: 2/13/2002 5:58 PM
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 1
Here is a link to some very good tutorial info about the different type of scopes and their advanatages and disadvantages:

http://www.astronomics.com/main/howto.asp?n1=1&t1=4&cat%5Fid=4

Things to consider in buying a scope include (IMHO):

1. Aperature - the larger the size the more light collected, the brighter the image.
2. Portability - Do you live in the city or country? The most important factor in what you see when viewing deep sky objects is the amount of light pollution. A smaller scope is more portable and easier to set up at a dark site. This is obviously a trade off between 1 and 2, but can also depend upon the type - Catadioptric is an option where you get more aperature for the total size.
3. Quality - of optics and steadyness of the mount.
4. Computerized or manual - if you are new to astronomy you may want to consider a GOTO scope, especially in the city where it is harder to star hop and find fainter objects.
5. Once you get the scope you will want to start looking at quality eyepieces which can greatly improve your views.

Just a few random thoughts. Email me if you have more questions. I have a Celestron Nexstar 5 which I love - great trade off of size and portability and ease of use.

-KQ



Print the post Back To Top
Author: TMFOrangeblood Big gold star, 5000 posts Old School Fool CAPS All Star Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 146 of 1797
Subject: Re: Telescope talk Date: 2/13/2002 6:12 PM
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
Here is a link to some very good tutorial info about the different type of scopes and their advanatages and disadvantages:
http://www.astronomics.com/main/howto.asp?n1=1&t1=4&cat%5Fid=4


I was about to ask for some replies again, and the appropriately named Messier101 comes through!

Thanks for the link, I'll definitely poke around the site. I suppose at this point I'm trying to decide between the two 8-inchers at the bottom of this page:
http://www.telescope.com/cgi-bin/OrionTel.storefront/3c6a0e05000f5c8a2720c0a80a12060a/Catalog/AE

I'm leaning heavily toward the $529.00 Orion SkyView Deluxe 8 EQ Reflector, because it's more portable, and I'll be able to do some photography through it.

My main questions would involve any advantages/disadvantages of such a "fast" scope (f/4). But for the money, I've not seen anything comparable. (Also, I don't want a GoTo scope at this point... I'd rather learn the sky.)

Jim, do you or you wife have any thoughts?

Thanks again,

orangeblood


Print the post Back To Top
Author: jiml8 Big gold star, 5000 posts Old School Fool Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 147 of 1797
Subject: Re: Telescope talk Date: 2/13/2002 6:56 PM
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
Jim, do you or you wife have any thoughts?

A fast newtonian will give you coma error for off-axis images. How much of a problem this is depends on what you want to do. For deep sky faint images you'll never notice it. Looking at things like open clusters, it will be quite visible. For planetary observations, you will probably want to mask it down.

I think I would pay more attention to the mounts (both scope mount and mirror mount) than anything else (after, of course, selecting aperture). For equal $$ I would probably go smaller aperture to get a better mount. Of course, the ideal is to get the biggest aperture you can (you can always mask it if you need to), but a shakey mount or an unreliable mirror mount will ruin the experience.

The scope we have here is a 9" Schmidt-Cassegrain reflector.

Print the post Back To Top
Author: Messier101 One star, 50 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 148 of 1797
Subject: Re: Telescope talk Date: 2/13/2002 7:37 PM
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 1
My main questions would involve any advantages/disadvantages of such a "fast" scope (f/4). But for the money, I've not seen anything comparable. (Also, I don't want a GoTo scope at this point... I'd rather learn the sky.)

A few other thoughts.

Coma as Jim stated, gets worse as the scope gets faster, so that is a disadvantage.

The F4 is designed for visual use, photography is a secondary consideration. Coma will show up more on photographs, you won't notice it as much visually.

At 800mm focal length, this is a scope designed for wide field deep sky objects which you will need a dark site to use. With the 9mm EP you only get 89x power which is not very good for viewing the moon or planets. Also the eye relief stinks on a 9mm plossel, especially if you wear glasses. I had a 10mm Plossel that I sent back because it was too uncomfortable to use, even without glasses.

If you are anywhere near DC you will need to go out to the country to get a good dark sky to fully use the scope. That is where portability and setup become an issue. The best scope is the one used most. If a smaller scope which is easier to move and set up is used more than a large scope then that is a better scope for you.

This is why I got a 5" instead of an 8", I can keep it set up in the house and walk out to the back yard and plop it down and be viewing in 5 minutes. It is also small enough to take camping. But a 5" under a dark sky will be more satisfying than an 8" under a suburban sky.

If you have not looked through a lot of different telescopes, the best thing to do is find a local astronomy club and go to a star party. You will be able to try out a large variety of scopes and see how big they are and how easy they are to set up.

One last thing with regard to GOTO scopes. There are 2 schools of thought. The first is you need to learn the sky and therefore GOTO is bad, the second is that a GOTO scope will help you learn the sky. I subscribe to the second view. One of the most frustrating things to a beginner is finding things to look at, especially if you are in an urban or suburban location. It can be very hard to find anything but the brightest stars and constellations. A GOTO scope helps keep the interest level up while learning the sky at the same time with a good sky map. The best telescope is a telescope used often, not one that sits in the closet gathering dust.

Hope I didn't ramble too much. Again, these are just my opinions. Good luck with you research.

-KQ

Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Print the post Back To Top
Author: MainiacJoe Big red star, 1000 posts Old School Fool Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 152 of 1797
Subject: Re: Telescope talk Date: 2/14/2002 11:56 AM
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
The January 2000 issue of Sky & Telescope had a review of 6 8" Dobsonian reflectors. The Orion came out ahead. I've used a 6" version that I reccommended to a friend, and I had few complaints about it and the friend was very pleased. The Orion Dobs are the best values out there, hands-down. Not the best scopes, of course, but you do not get more for the money anywhere, and none of it is trash.

- Joe

Print the post Back To Top
Author: TomoBedlam Two stars, 250 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 175 of 1797
Subject: Re: Telescope talk Date: 2/22/2002 2:24 PM
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 2
For what it may be worth, I bought an Orion SkyView Deluxe 8" EQ Newtonian back in November. I wouldn't consider myself an especially experienced astronomer, having been an enthusiast in high school and only just recently started to get back to it (after a 25 year hiatus) but I've really been quite pleased with the observing I've done so far. I did go ahead and buy a laser collimator for it, which has made collimating it a relatively painless experience. The telescope does seem to require collimating pretty frequently, which could get annoying if you had to do it the old fashioned way. Stability of the mount has not been too much of an issue as far as wavery images go. The mount does tend to fall over when you lift the telescope off of it (high center of gravity from the counterweights.) I have yet to try photography with it. I'm anticipating not being able to do really long exposures, due to instability and the clock drive probably not being accurate enough. I do plan to try some lunar and planetary things. Just my two cents' worth...

Print the post Back To Top
Author: TMFOrangeblood Big gold star, 5000 posts Old School Fool CAPS All Star Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 180 of 1797
Subject: Re: Telescope talk Date: 2/23/2002 2:34 PM
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
Stability of the mount has not been too much of an issue as far as wavery images go.

That was something I wondered about. You'd think they wouldn't sell you a mount that wasn't steady for the particular scope, so I'm glad to hear it's okay.


I have yet to try photography with it. I'm anticipating not being able to do really long exposures, due to instability and the clock drive probably not being accurate enough. I do plan to try some lunar and planetary things.

Let us know how it works out whenever you do try it. From what I've read, you probably need to perform some manual adjustments on really long exposures, by keeping a "guide star" centered.

Also, I've read that the actual focusing point of some Newtonians do not extend outward enough to reach the camera's film plane. I don't believe that will be an issue with the SkyView, but please let us know that as well.

Thanks,

orangeblood

Print the post Back To Top
Author: RBrowndog One star, 50 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 227 of 1797
Subject: Re: Telescope talk Date: 3/15/2002 3:42 PM
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 1
The Orion 8 inch Dob is a nice telescope. I've spent much time looking at telescope reviews etc. So far all I own is a great pair of binoculars. Here is my opinion of what I've concluded...

The 8 inch Orion Dob is great for beginning. There are things that do need tinkering. However, it is a good telescope to tinker with. Kinda like a really great reliable used car that doesn't need repair, just some tinkering. People I've read who own them really like them. They have a discussion group on Yahoo. They seem fun.
The mount you'll get with that 8 inch Orion reflector just won't cut it. It is obviously a cheap one. Especially for photography. You'll have to pay for a good steady mount.
From what I've looked at... I've narrowed down my preference to two telescopes... and most probably the Four inch Dobsonian listed below...this thing is HOT. For it's size it kicks hiney! If you want quality for the money, this is it!
http://users.erols.com/dgmoptics/
Also this refractor is great for the money...would seriously consider it...A great value...
http://www.stellarvue.com/102d.html

Yes, I do think the two I mentioned here are the best value for the money there is. I don't think I would ever want to sell one of them in preference for another telescope. I may buy another telescope, but not sell one of those.

Ron



Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Print the post Back To Top
Author: TMFOrangeblood Big gold star, 5000 posts Old School Fool CAPS All Star Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 229 of 1797
Subject: Re: Telescope talk Date: 3/15/2002 11:16 PM
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
I've narrowed down my preference to two telescopes... and most probably the Four inch Dobsonian listed below...this thing is HOT. For it's size it kicks hiney! If you want quality for the money, this is it!
http://users.erols.com/dgmoptics/
Also this refractor is great for the money...would seriously consider it...A great value...
http://www.stellarvue.com/102d.html


Hi Ron... interesting stuff.

I have to tell you, though, I can't see paying two or three times more than the Orion for one of those scopes, especially when they're only 4-inchers. I'm sure they're better quality, but I don't know about better value.

I've subscribed to the astrophotography mailing list, and I'll share some of their insights regarding telescope selection in a later post.

Thanks for all the good info...

orangeblood

Print the post Back To Top
Author: rodgpetersen Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 408 of 1797
Subject: Re: Telescope talk Date: 6/28/2002 3:16 PM
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 1
O couple of things to keep in mind...

Fast scopes ( low F# ) are very difficult to figure, so your average commercial F4 is going to be a fairly crude mirror, good for low power sweeping and with a VERY good mount, astrophotography. Collimation is going to be a rip-snorter, especially for newbies.

I haven't seen any reccomendations to "roll your own". Here's one. Your first mirror, with a bit of patience, is going to be an order of magnitude better than popularly priced commercial mirrors. You can make a nice 8" dob using excellent parts (something commercial scopes seldom have) for a couple hundred dollars. With a bit of patience, a first mirror can fairly easily be 1/10th wave, most commercial stuff tests out at 1/2 to 1/4 wave and a lot of us have tested mirrors for unhappy owners with over 1 wavelenght of error.

Here it comes, make yourself a nice little 6"F8 or 8"F7 dob, easy to make, easy to use, both will fulfill a lifetime of viewing.
Rodg in Bellevue

Print the post Back To Top
UnThreaded | Threaded | Whole Thread (11) | Ignore Thread Prev Thread | Next Thread
Advertisement