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Difference between 8 inch and 10 inch Dobsonians

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#26 Jon Isaacs

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Posted 04 May 2017 - 03:11 PM

I think if I had to assemble a truss-tube every time I used my scope, I would go from observing every chance I get to only 3-4 times a year.  So, for me, a truss tube would never do as a primary scope. This kind of sets an upper limit of 10 inches for me.

 

You don't have to assemble a truss scope to use it.  Just because you can disassemble and reassemble a truss scope,  it doesn't mean you have to, it just means you can. 

 

Tossing a 16 inch tube scope in your car ain't gonna happen, it's easy with a truss..  Wheeling a 16 inch truss out of the garage out to the backyard,  that might take 5 minutes.  

 

Two nights ago,  I brought my 12.5 inch truss to town to do some work on it.  I took it apart to put in the back of the truck.  When I got home,  I assembled it to work on it.  Then I just carried it out back like I would a tube scope.. 

 

Of course the effort required to setup a truss can be overblown,  some scopes are easier than others.  I take my 13.1 inch apart because it's so easy..  I once timed myself..  Scope in parts in the scope room to scope assembled in the backyard..  Less time than 3 minutes. 

 

I do enjoy large aperture scopes and being retired and living where I do, I get to use them a lot.. Larger scopes are more effort but there's a reward that comes from having made that effort.. 

 

Jon


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#27 dr.who

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Posted 04 May 2017 - 03:29 PM

If size and bulk are a concern then you should look at the Explore Scientific Compact Dob's. Both the 10" and 12". You may find that the 12" isn't as bad as you thought but if you do their 10" is a good option for portability.
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#28 leetje

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Posted 24 April 2018 - 09:00 PM

I made the mistake (in my case) of jumping from a 8" Orion Dob to a 12" Orion Dob. I didn't seriously consider how much bigger and heavier it would be for me. The scope alone without the mount was as heavy as the 8" scope and mount. and significantly bulkier. If I had to do it all over again I maybe would have tried a 10" upgrade instead. I probably would have used it a lot more. But I probably shouldn't have bothered to upsize at all in my case.

Consider this before you do it: Is there ever a good observing night where you just don't feel like lugging out the 8"? If there is, then you may want to reconsider upsizing. Because if you feel that way 5 times a year with the 8", you'll feel that way 20 times a year with the 10".

This is very helpful advice. I currently own an 8 inch Dob (Apertura AD8), my first telescope and I have enjoyed it very much for the past few years. On dark nights I get very nice views of the galaxies, planets (especially Jupiter, Saturn) and nebulae. The working useful range of magnification with this f6 scope is conveniently wide, 30-180x. While I sometimes wish I got the 10 or 12 inch versions for more light gathering, for the more dim nebulae and star clusters, the 8 inch is about as heavy as I would want for a portable telescope, taking it in and out of the car/camper etc. I am reminded of this every time I move it. I can take it out of my house to my deck in one piece, awkward but doable, something that would be impossible with the 10 or 12.  That all said, when I look through larger aperture Dobs at star parties (i.e. like the Obsession 12, 18), I can really see the difference and start to think to myself that it would be nice to have a larger one, with more bells and whistles like go-to, tracking.  So I have been mulling whether to upsize or carry on with my 8, which I love.  Based on yours and other posts, I'm inclined to stick with the 8. Like everything else, its a trade-off: weight/portability vs. aperture/light gathering.



#29 dgoldb

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Posted 24 April 2018 - 10:23 PM

If I already had an 8" with good optics, I wouldn't go to 10" for the increase in aperture alone.  It would have to come along with a better structure, optics, etc.  I guess if I could sell the 8" and get the 10" for nominally more $, I suppose it is worth while.  But I probably wouldn't bother.  Too much hassle.  Not enough juice for the squeeze. 


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#30 Deep13

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Posted 24 April 2018 - 11:57 PM

I've got an 8 solid tube and a 12.5 truss. Guess which one I use twice per year at Cherry Springs and which I use often. From 8 to 12.5 is about one magnitude, so 8 to 10, I'm thinking is about half a magnitude.
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#31 Pinbout

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Posted 25 April 2018 - 08:45 AM

 

While I sometimes wish I got the 10 or 12 inch versions for more light gathering, for the more dim nebulae and star clusters, the 8 inch is about as heavy as I would want for a portable telescope,

12in's doesn't have to be that heavy

 

https://www.youtube....h?v=O8EKNknHjG8



#32 Eddgie

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Posted 25 April 2018 - 08:58 AM

While I understand the OP's concern about the size of the 12", I too would be in the camp that says a modern ultra-light 12" is really no bigger and heavier than a 10" and can actually be lighter and easier to move.

While the step from 8" to 10" is a decent one, a 12" ultra-light is in a different class.

 

Just because it is a truss tube does not mean you have to take it apart when you are not using it in exactly the same way you don't (and can't) take apart a 10" solid tube scope.

 

The modern ultra-lights are often a bit faster as well, meaning that you can use less expensive eyepieces and still get very big exit pupils.

 

The first time I saw a modern ultra-light 12" dob in person, I was quite amazed at how compact and light it was.

 

Modern mass produced dobs use MDF mounts, and these are heavy and clumsy to move.   By comparison, modern ultra-light bases are super compact and light. 

 

If I were going to make the step, the only time I would go for thee 10" is if the budget forced it.  Otherwise, I would perhaps save until I had enough to get a good ultra-light 12".   This is a considerable step up from an 8" and in a package that is pretty painless to move and store.

 

Look at the specs on some of these scopes and compare to a mass produced 10"...

 

http://www.dobstuff.com/measures.htm

 

Not that the move to 10" won't give some improvement in viewing, but it is a half step at best, and may not prove to be as satisfying as some post suggest.   Sadly, this is one of those things that people usually have to see for themselves to judge if it was worth doing.  From 8" to 12" though is a much more obvious and dramatic step that anyone will see.


Edited by Eddgie, 25 April 2018 - 09:05 AM.

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#33 macdonjh

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Posted 25 April 2018 - 10:33 AM

I will take the OP at his word that he's done his homework and is satisfied a 10" scope is all the upgrade he wants to consider.  My C11 was a significant and noticeable improvement in viewing over some friends' C8s.  Familiar objects were brighter and more enjoyable to look at, AND objects that were too faint to be interesting to me opened up and became targets I sought out.  Very worthwhile for me.  Skip forward a few years to a shoot-out between my C11 and a 10" scope.  The 10" scope won for cool-factor and my perception that the image wasn't degraded by the loss of 1" aperture.  I sold, with a heavy heart, my C11 and kept the 10".

 

That's a long, round-about way of saying that for me, a 10" scope is a worthwhile upgrade over an 8" scope for deep sky. 

 

To confuse things, I am perfectly happy with my 8" driveway scope for lunar, planetary and double stars.  I never used my 10" or 11" scopes at home because they needed my G11 which was a pain to assemble and set-up for an hour's viewing (I know, not a problem for our Dobsonian-owning OP).  My 8" driveway scope requires only an Orion Sirius which I leave assembled and carry out of my garage in one trip, gives satisfying resolution (560x was not empty magnification on two near-perfect nights, 240x regularly), and provides images bright enough to trigger even my lazy color receptors so Jupiter and Saturn are more than just yellow and brown.  So, there's my case for the 8" scope, if you're a lunar/ planetary observer.


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#34 Pinbout

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Posted 25 April 2018 - 12:13 PM

Familiar objects were brighter and more enjoyable to look at, AND objects that were too faint to be interesting to me opened up and became targets I sought out.

 

globs start to become alive in 10" and above.


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#35 tommy10

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Posted 15 August 2018 - 02:30 PM

globs start to become alive in 10" and above.

 

Globs come alive when your looking at them under a dark sky, from the LP suburban skies, they are up against a greyish background, m M4 is basically invisible, M12, M-3, M-15,M -92, a couple of others are visible ,but why buy a scope to see a handful of dull objects that will look the same every time you look at them .



#36 stargazer193857

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Posted 15 August 2018 - 08:27 PM

I have owned an 8 inch Dobsonian for a decade and am thinking about upgrading to a 10 inch one (the 12 inch is too large for me to transport). Is there a perceptible difference between an 8 inch and a 10 inch reflector or should I save my money for something else?


Yes. Don't let these guys tell you not to upgrade because it is not a full magnitude. Get the scope that is the best trade off for you between performance and transportability. Swapping and paying for a modest improvement goes against some advice, but you will be happier in the long run.


That said, I don't like commercial 10" dobs. Their base is too big and their mirrors too thick. By the time you replace that you might as well start custom. The 8" is sized right on both metrics, but noticeably dimmer. The 10" still is manageable even commercially.

#37 SpaceConqueror3

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Posted 15 August 2018 - 09:30 PM

I haven't done much comparative viewing between an 8" and 10" dob but I remember being at a Star Party and looking at 10.5-11.0 mag comet in my 10"Dob.  When a guy setup near me asked for help finding it in his 8", I was just barely able to see it in his scope and only because I knew exactly where to look for it. I would have never found it otherwise. ​But in my 10" it was easy to see.



#38 stargazer193857

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Posted 16 August 2018 - 12:45 AM

The ring nebula is puny in 8". It looks interesting though no color in 10".

M51 has clear structure, no color, in 10". It is dim in the 8".

There really is a noticeable difference. 8" is cheap and what a semi serious newbie buys for Christmas. 10" is what you buy to impress the public.

Does not matter if SCT or newt. I compared them all.


As for coma, an Explore Scientific or Meade will lack astigmatism in both, but the f5 has coma outside 41 degrees, and the f6 has it outside 60 degrees.
I would not buy a coma corrector for f6, but you can see it if you want to. As for the double cluster in the f5, you can fit it all in the middle 50%, but will have to track. The coma still is not so bad in peripheral vision.


The main concern is the 10" base stock might not fit in your truck on its side if you have a medium or smaller car trunk.

#39 stargazer193857

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Posted 16 August 2018 - 12:50 AM

4-8" have their uses. Easy transport, lower price, maybe wider views.

For me they were teasers to get into the hobbie and see stuff and learn want I want. I learned alright.

My friend said 12" f5 is optimal view for effort after looking at many, but I don't like the high eyepiece and other factors. I plan to do 11" f4.5 custom, to get the best of all worlds. Taller people may go taller. For wide views, I go refractor.

#40 JohnnyStargazer

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Posted 16 August 2018 - 12:28 PM

There's a perceptible difference in the views offered by 8" and 10" dobs, but I find there's also an equally perceptible difference in the portability and transportability of these two scopes, so an 8" scope is still the largest scope that I own, and a 6" scope is my most used scope. 

I have a 6" ,10" and recently got a 8" .

Really been enjoying the 8.



#41 Jon Isaacs

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Posted 16 August 2018 - 12:38 PM

The ring nebula is puny in 8". It looks interesting though no color in 10".

M51 has clear structure, no color, in 10". It is dim in the 8".

There really is a noticeable difference. 8" is cheap and what a semi serious newbie buys for Christmas. 10" is what you buy to impress the public.

Does not matter if SCT or newt. I compared them all.

 

 

Wow , Just Wow.

 

"What a semi-serious Newbie buys? " Get real. An 8 inch is a very capable scope and a can be lifetime scope for a serious observer. 

 

No one has compared them all.  To say there's no difference between an Newt and an SCT one has to have a rather undiscerning eye.  

 

My friend said 12" f5 is optimal view for effort after looking at many,

 

 

"Optimal view" is subjective.  I've looked through more than a few,  owned quite a few , currently,  I own five Dobs.  They all provide optimal views,  optimal viewing comfort in specific situations.. 

 

Jon


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#42 gwlee

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Posted 16 August 2018 - 01:52 PM

You don't have to assemble a truss scope to use it.  Just because you can disassemble and reassemble a truss scope,  it doesn't mean you have to, it just means you can. 

I had a small truss scope for a few years that I usually left set up in the family room because I used it most nights. Spiders loved building webs in it and frequently made a mess of it. Never gave spiders a thought until then. Found it much easier to exclude spiders from a solid tube Dob.  


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#43 Brapp

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Posted 17 August 2018 - 10:45 PM

Don Machholz discovered a comet with a 5" scope made out of plywood and plumbing pipe.
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