Posted 01 August 2014 - 04:58 PM
First question I have is about aperture and brands. I've been looking mostly at 8" orion skyquest and the 10" meade light bridge.
How much of a difference is there between 8 and 10? Which scope is made better? Is a truss dob. more trouble than its worth?
I'll be moving up from a 70mm refractor and a 3" reflector. So that's going to be a rough increase of about 568% for 8" and 944% for 10". Either way I'm going to see a huge increase in what I can see but I'm mainly interested in viewing deep sky objects. Is 8" enough?
The other thing is I wanted to buy local at first, for two reasons. First to support local business and second to avoid getting a damaged scope in the mail. But now I think I'll buy online.
The local place wants $508 (after tax) for the 8" Orion which Orion sells for $350 (no tax + free shipping). Meade Lightbridge would be $822 after tax. Meade and telescopes.com sell it for $599 (again no tax and free shipping). They say its because they assemble it and collimate it with their "proprietary" collimation technique.
Since I've never collimated a telescope because the 3" reflector I use from time to time is my dads, I looked up collimation on youtube. It looks pretty simple.
If it was just $50 extra or even $75, I'd go with the local place. But online, for that much money, I could get the telescope, a laser collimator, and an extra eyepiece.
So is setting up a new dobsonian for the first time difficult enough to justify a $150 - $220 price increase?
Or is likelihood of damage during shipping enough of a concern?
Thanks for Your time.
Posted 01 August 2014 - 05:14 PM
- jgroub likes this
Posted 01 August 2014 - 05:19 PM
1st- you have to collimate a dob all the time anyway so dont let that collimation thing sell you.
10" is better but 8" is easy to carry around.
Even a 6"f5 on a alt/az mount will show you a lot.
- maakhand likes this
Posted 01 August 2014 - 06:17 PM
I've owned both 8 and 10 inch dobsonian scopes
and here is my 2 cents.
1. There is a slight but noticeable difference between an 8 and a 10 inch. To me the difference is worth it if you can afford it.
2. A truss is not necessary for a 10, a solid tube is just fine, and less expensive. The overall length of the tubes is equal and the weight difference is not that much of a factor. If you travel with it in an automobile they both take up nearly the same space True the collimation of a 10 inch f/4.8 is more critical than an eight inch f/6 but it isn't that much more difficult and after several times you will get the hang of it.
3. Both the 8 and 10 are a HUGE improvement over a 6 inch.
- maakhand likes this
Posted 01 August 2014 - 06:18 PM
Posted 01 August 2014 - 06:29 PM
I am biased toward getting the largest possible aperture because of the main objects I look at (faint fuzzies). I love my solid tube 12". 8" and 10" tubes are MUCH easier to manuever. Either will fit in the back seat of most vehicles. Collapsible tubes of 8" and 10" scopes aren't that much smaller than their solid siblings. Collapsibles begin to have the advantage at the 12-and-above level.
I admire and respect your desire to buy local but the differences you've found are significant. If you have the committment to this, I'd be up front with the local businesses. Ask them if they would be willing to meet you in the middle, so to speak. You're not trying to low ball them. They need to make a profit and you're not made out of money.
Collimation is important, fast, fun, and easy if you use the right equipment. The lasers supplied with most dobs are not reliably collimated themselves. Plan on upgrading to better equipment. The views will make it worth the cost. If you have a club or individuals that already own collimation equipment, many/most will gladly show you how to use it and will gladly loan you theirs.
- maakhand likes this
Posted 01 August 2014 - 06:40 PM
If you go with the 8" you can safely use cheaper eyepieces. The 10" will require more expensive/better corrected eyepieces.
Over the years, I have owned a number of Dobsonians, currently own five.. It is true that at F/5, many eyepieces will show somewhat more off-axis astigmatism that at F/6 but in my mind, that does not mean that the faster F/5 scopes "require" fancier, more expensive, better corrected eyepieces. It just means the there's a little more off-axis astigmatism, stars near the edge are not a round and clean. I have some rather nice eyepieces that I typically use, TeleVue Naglers and a Paracorr to correct the coma, but some nights I will use a set of simpler, more affordable eyepieces, for the higher magnifications I use the TMB Planetary eyepieces and they do a very reasonable job, not as wide a field of view nor quite as perfect as the Naglers but there is little I see in the more expensive eyepieces that is not visible in the TMBs.
Regarding the difference between the 8 inch and the 10 inch... For me, not a spring chicken by any means, 66 years old, social security and all that.. The 10 inch is heavier and somewhat more bulky but the 8 and 10 inch OTAs are about the same length and the bases are about the same size. That means when it comes to putting one in a car or setting it up in the backyard, there isn't much difference.
At the eyepiece, the difference is quite apparent. It's not like the difference between 3 inch and a 6 inch but the added aperture is definitely worth while. I have my 10 inch GSO Dob for more than 10 years. During that time, several 8 inch F/6 Dobs have come and gone. I could just never find a reason to choose the 8 inch when the 10 inch was there just waiting.
The photo below shows three scopes, an Orion XT-8 (F/6) on the left, a 12.5 inch F/4.06 Discovery in the middle and a 10 inch F/5 GSO (Zhumell/Apertura etc) on the right.
- maakhand likes this
Posted 01 August 2014 - 07:58 PM
Posted 01 August 2014 - 08:18 PM
- LDW47 likes this
Posted 01 August 2014 - 08:45 PM
I recommend getting a scope with the dual-speed focuser as it is MUCH easier to get precise focus.Since Zhumell is no more then look at Apertura or the astronomics brand Astro-Tech.
If you think you will get a 12" in the future and also keep the 8",get the 8" now.Or you can sell the 8" after getting the 12" and not lose too much money.
If you expect to have only one,get the 10" now.
Honestly the only thing I thought terrific about the Orion XT8 was the little knob makes it so much more natural to move the tube when following an object-and that can be added to any other brand.Can't say the view was better or worse than other brand of the same size.
Posted 01 August 2014 - 08:51 PM
Differences? The 10" provided brighter images and saw a lot more deep sky from my red zone home. The 8" had a much sharper image. The 10" was rather heavy to carry out to an observing field at a dark sky site. At my red zone home it was a trivial difference to drag outside.
10" sees more than 8". No matter where you observe. At my age, however, 10" is too much to travel with. And at F6 the 8" will provide a better image than the F4.7 10". No matter what eyepiece you use. (Parracors change that equation.)
I was happy with both of them. You can't really go wrong with either. Good luck!
Posted 01 August 2014 - 10:15 PM
Posted 01 August 2014 - 10:24 PM
-collimation isn't difficult, just critical
-you won't BELIEVE how much cool stuff you'll see
-don't fret too much, have fun
welcome to deep sky observing!! and good seeing to us all.
Posted 01 August 2014 - 10:30 PM
Zhumell scopes are sold by Hayneedle who is like a big online department store, which appears to be getting out of the telescope business. The AT by Astronomics and Apertura by Opticsmart are sold by fully capable and well respected astronomy vendors and are greatly appreciated by many in the community. Orion and SkyWatcher Dobsonian scopes are made by Synta which are also well respected in the community as good vendors with good products.
So, it really comes down to what packaging features and price works for you, you'll get a good scope from any of them along with the support you need. Hayneedle basically just takes returns or exchanges, they don't provide much astro specific support, but I haven't heard of anybody having issues returning items that were damaged etc...other than some who received damaged items multiple times in a row. But as far as I know they eventually got a good delivery or were always refunded without issue.
Posted 02 August 2014 - 04:17 AM
The 10 inchers' advantage when viewing the globs, it seems to me, is because resolution increases with increasing aperture. The ten begins to resolve more of our accessible clusters into individual stars at the right magnification. Maybe it is the combination of resolution and brightness of the image?
Anyway, I just love the esthetics of those sparkling mounds and to be able to resolve the component stars is icing on the cake.
Posted 02 August 2014 - 04:25 AM
Weight is not a concern. Size is not a concern (between the two). Price is. Quality of image is.
If size and weight aren't issues, I would prefer a solid-tube scope to a truss-tube scope in any size up to 10 inches. (Beyond that, solid-tube Dobs get really awkward.) However, that's partly because of my climate and location.
In my part of the world (eastern U.S.), dew and condensation are constant worries. Solid-tube Dobs are nearly immune to dew. And when bringing them inside in the winter, just put a shower cap over each end, and all the cold, dry air will be trapped inside, eliminating any chance of condensation on the mirrors. Condensation on the mirrors is a serious problem when bringing an unsealed scope inside in the winter.
Price speaks for itself. As for image quality, all other things being equal, a 10-inch Dob should have identical image quality to an 8-inch Dob.
Will I have enough clusters, nebulae, galaxies to look at to keep me busy for a while if I go with 8"?
Absolutely! I could easily spend the rest of my life exploring the night sky with an 8-inch Dob, and I would never run out of new things to see.
Mind you, this depends very largely on light pollution. You're not going to see much detail in galaxies or nebulae from a typical suburban location no matter how big your telescope is.
The difference between an 8-inch and a 10-inch isn't so much how many extra objects the 10-inch will show, but rather the extra detail you will see in the 10-inch. The difference is most apparent on globular clusters, many of which happen to be near the edge of resolution through an 8-inch scope from a suburban location.
I find the f/5 f/6 talk a little confusing still. I know its a focal ratio and all and basically what it means... but how it applies to viewing experience, no.
Not much, if anything. Once the scope is properly collimated, a telescope is a telescope. Viewing through the eyepiece, you'd have a very hard time guessing if a scope is f/5 or f/6.
Posted 02 August 2014 - 07:23 AM
- jgroub likes this
Posted 02 August 2014 - 03:20 PM
I have no long tube to lug around and try to stuff in the back of something. It doesn't affect a thing as far as collimation is concerned anyway. You're going to have to do it regardless. Just moving your scope out in the back yard will make you have to do it whether you have a solid tube or trusses, so why not go for something you can break down a bit?
I already have a 16-inch f/6.4 that I built from the ground up, including the mirror, and it's a solid tube nine feet long. It's a tad weighty to say the least! My wife is the one that green-lighted the Lightbridge and I'm glad because it's a lot easier to move around and a lot more compact. The 10 and 12-inchers are even more so.
Let the naysayers have their fun, but that's what I think.
Posted 02 August 2014 - 04:06 PM
For that kind of money you can buy the finest collimation gear available and have it forever, since collimation needs to be redone regularly making their supposed fancy job worthless.
Either of the scopes will do fine for you, the 10" actually has roughly 50 percent more surface area than the 8", so it gathers more light which is great for faint objects. It won't make much difference on the moon or planets though, so it matters what you like to observe.
I don't find either big or heavy. I have a 12" that's easy to move around, while the 16" is difficult, it just depends on how good of shape you're in and how far you have to move it.
Don't stress too much about it, you'll be happy with either one. If you like it you'll probably end up getting a 12" in a while anyway, which is a great all-around size.
Posted 02 August 2014 - 04:06 PM
Apertura scopes are very well made and are sold by a very respected company that has gotten the highest reviews on this site. The owner of Opticsmart is also a member of Cloudy Nights and answers peoples questions from time to time. I have the AD8 with the tweakers dream package and it is a very good scope.
I saw the Apetura Dobsonians at NEAF and was immediately impressed with the features. The movement in both axis were smooth and if I were looking for an 8 or 10 inch dob today, I'd grab one in a heartbeat.
- lamplight and jgroub like this
Posted 02 August 2014 - 04:22 PM
Posted 02 August 2014 - 07:46 PM
A few months ago I had never heard of collimation before, let alone say it three times really fast. There's a lot of disagreement about those "fancy tools" to meet that perfect mirror alignment. Like Feidb had just mentioned, I also use that cheap plastic collimation cap that came with my scope. My views have been wonderful and the it takes only a minute to do it. I don't think I'll ever buy a special tool for that job. Why should I buy something to fix something that's not broken?
How sure are you that your collimation is within tolerance? For deep sky, precise collimation is not necessary but for double stars and planetary viewing, it's got to be within a fraction of a millimeter.
- Feidb likes this
Posted 02 August 2014 - 08:20 PM