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Difference between 8 inch and 10 inch Dobsonians

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#1 Lucas Bittar

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Posted 22 April 2017 - 06:40 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?



#2 J A VOLK

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Posted 22 April 2017 - 06:46 PM

yes - very perceptible, 25% increase in resolution and 56% more light. Observed recently with my 10" and friends 8" near by - very noticeable difference.
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#3 jjt312b

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Posted 22 April 2017 - 06:51 PM

Lucas,

 

Thanks for this topic. Was thinking about doing the same. Will follow this.


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#4 UAwildcat

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Posted 22 April 2017 - 07:01 PM

I certainly noticed a difference moving from an 8-inch Dob to a 10-inch Dob. Very worthwhile. I think your conclusion about passing on the 12-inch is something a lot of people do because of 1) the longer focal length and 2) the extra weight. Those two issues are significant considerations for ease of transport. 


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#5 Adun

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Posted 22 April 2017 - 07:03 PM

I've read quite a debate about 10 vs 12 as an upgrade for 8".

 

10 is said to be a good upgrade, but many folks recommend 12 as a better one. But then, transportability is an issue, and then other folks mention the truss and collapsible options, and some argue they are even easier to transport than an 8" solid tube.


Edited by Adun, 22 April 2017 - 07:06 PM.

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#6 tomykay12

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Posted 22 April 2017 - 07:29 PM

I have a 10" dob. It has been said that 10" is the largest of the small dobs and 12" is the smallest of the large. I wouldn't want to move a 12" or larger unless it was a truss/lightweight setup. Having not looked thru an 8" dob, I can say the 10" is pretty nice. My understanding is the physical size difference between 8 and 10 is not much, so why not have more aperture for very little hassle factor? Just a thought. 


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#7 precaud

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Posted 22 April 2017 - 07:32 PM

Yes, there is for me. Deep-sky observing really starts to come to life with a 10. And in good seeing, it outperforms the 5-6" class ED fracs on planets. I think the 10" dob occupies a unique niche among telescopes. Anything bigger becomes cumbersome to handle solo. Anything smaller leaves me wishing for something bigger too often.

 

If I had to live with just one scope, it would be a good 10" dob.


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#8 Not Here Anymore

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Posted 22 April 2017 - 07:44 PM

2 inches!

 

But seriously, I did the Herschel 400 with a 10" to get one the Astronomical League certificates.  10" is noticeably different from 8".  In fact, it is an ideal size that does well for planetary and deep sky.  I would highly recommend going to 10".


Edited by JCAZ, 22 April 2017 - 07:47 PM.

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#9 jjt312b

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Posted 22 April 2017 - 07:57 PM

JCAZ, on 22 Apr 2017 - 8:44 PM, said:

2 inches!

 

But seriously, I did the Herschel 400 with a 10" to get one the Astronomical League certificates.  10" is noticeably different from 8".  In fact, it is an ideal size that does well for planetary and deep sky.  I would highly recommend going to 10".

That's what she said...

 

But seriously too, I think I'm already convinced to upgrade. What do you think Lucas? 


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#10 Jon Isaacs

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Posted 22 April 2017 - 08:12 PM

I have a 10" dob. It has been said that 10" is the largest of the small dobs and 12" is the smallest of the large. I wouldn't want to move a 12" or larger unless it was a truss/lightweight setup. Having not looked thru an 8" dob, I can say the 10" is pretty nice. My understanding is the physical size difference between 8 and 10 is not much, so why not have more aperture for very little hassle factor? Just a thought. 

 

I have had my 10 inch F/5, "$240 on Astromart" for about 15 years.. It's basically the same scope as the Zhumell.  It has never been my largest scope but it's a good scope and easily transported and carried. When I bought it, I had an XT-8 which I eventually donated to a club, there never was a reason to choose the 8 inch when the 10 inch was right there.

 

There is a significant difference in the views but I do think it's worth considering a 12 inch truss style Dob. My 12.5 inch F/4.06 has a 19" x 20" footprint and nests in a package that's 28 inches tall.  

 

Jon

 

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#11 GeneT

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Posted 22 April 2017 - 08:15 PM

You have ruled out a 12 inch Dob. Maybe you could reconsider. A 12 inch gathers more than twice the light over an 8. You will notice quite a difference in all objects with a 12--if the optics are of good quality. I own a 12.5 inch Portaball, and it performs outstandingly on planets, globulars, open clusters, double stars, and fairly well on nebula and galaxies. Why would you rule out a truss tube? You could move up to a 12 truss from an 8, with ease of hauling, set up, take down, and storage. I store my 12 inch Portaball inside of my house on my side of the closet.  


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#12 bvillebob

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Posted 22 April 2017 - 08:31 PM

Having both 8" and 12" the difference is striking, while the difference between my 12" and 16" doesn't seem that great.  There are lots of lightweight designs, if it's possible for you to consider one of them i'd urge you to reconsider the 12" as an upgrade.  If you can handle it you'll be glad you did.

 

If you absolutely, positively cannot do a 12", by all means get the 10".  For me there's a real inflection point at 8" where every step above makes a significant difference.  My 8" dob is great, because my partner is 4'10" and it fits her perfectly smile.gif Other than that it wouldn't see a lot of use with the 12" in the house.


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#13 Subaru45

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Posted 22 April 2017 - 11:44 PM

I purchased my 10" f/5 4 years ago, and I'm quite happy with it. Going to be 72 in a couple of months and think that's the biggest I will go. I have been thinking about using it as a basis for a dual use scope, rather than using it for all types of observing. With its 12" tube I'd use it at f/5 for DSO's, then pull off both ends, ( primary mirror and secondary/spider/finder ) which would be replaced with 8"f/8 premium primary and matching upper end. This would be set up as an optimized planetary scope along the lines of that by Ed Grissom. The 12" tube giving the 2" clearance preferred by Ed. So, I guess I'd be using both an 8" and 10" rather going from an 8" to a 10".


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#14 Pierre Lemay

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Posted 22 April 2017 - 11:55 PM

I'm always surprised when this type of question comes up how many posters don't answer, proposing instead a larger scope than what the OP asked for. The same thing happened recently in this post which basicaly asks the same question: https://www.cloudyni...p-in-aperture/ 

 

There is definitely a big difference between an 8 and a 10 inch in terms of what one sees but also in the size and often weight of the instrument. Remember that bulkiness of a telescope increases approximately to the cube of the aperture for a given telescope type and focal ratio. 


Edited by Pierre Lemay, 22 April 2017 - 11:56 PM.

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#15 Max T

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Posted 23 April 2017 - 02:11 AM

I'm always surprised when this type of question comes up how many posters... propose instead a larger scope than what the OP asked for.

Perhaps to be motivated to post, it could be said that the forum posters are at the height of their astronomy enthusiasm and this spills over in their posts "get a 12 inch!"

It's all done in the best of intentions.

 

To offset aperture fever and add more realism to scope choices, I think a good notion is to always buy the next size down from the scope you're interested in.   

 

Desire a 10"?    Get an 8".   You'll use it a heck of a lot more.   

And what you lose in aperture can easily be overcome by modifying it into a high quality 8": premium optics, boundary side fans, 9 point cell, autocollimated, baffles and velvet, all thermal differences minimised.

 

And when all that is done, then it is possible to minimise defocus aberration too http://www.telescope...et/defocus1.htm

In other words, when you reach focus you can see pinpricks of threshold stars glistening in and out of view in the centre portion of your eyepiece field.    This is possible at f6 but it is easier at f8.

The views become very relaxing and contrasty.

 

Lucas- you might want to consider improving your 8" instead of buying a 10".

(I dropped from an 8" f6 to a 6" f8, so perhaps my bias is showing here).


Edited by Max T, 23 April 2017 - 02:16 AM.

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#16 Chesterguy1

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Posted 24 April 2017 - 11:46 AM

I like what Karl pointed out in the previous post.  There is more than the aperture gain to consider.  You make no mention of how far you plan to carry this scope or how often you plan to load or unload it.  All factors to consider.  I had a 10" that was admittedly an older sonotube variety and it was HEAVY and had to be split into two parts in order for me to carry it any distance.  I was younger and certainly fitter at the time.  I currently have an 8" that I can carry as a complete unit and can carry it for some distance without strain because of the lighter tube, mirror and base.  I might be able to do the same with a 10" from the same manufacturer, but it would be pushing it and I'm not getting any younger.

 

The point, which is often made here, is that there are always compromises.  I find myself using the 8" much more than my 15" partly because of the ease of set up, even though the 15" doesn't take that long.  Obviously if the night looks like it will really be great, I have plenty of time or I can travel to a dark site than it's worth it for the greater light grasp and additional effort of the larger aperture otherwise one can find and enjoy quite a bit with 8".

 

Chesterguy


Edited by Chesterguy1, 24 April 2017 - 11:47 AM.

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#17 earlyriser

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Posted 24 April 2017 - 12:00 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.


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#18 precaud

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Posted 24 April 2017 - 01:21 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.

Same here. And that's what stops me from trussifying (a new word is born) my 16" Newt. If I have to assemble/disassemble it with each use, I am pretty sure I wouldn't choose it often.


Edited by precaud, 24 April 2017 - 03:55 PM.

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#19 Tom_m

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Posted 24 April 2017 - 03:03 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.

Same here. And that's what stops me from trussifying (a new word is born) my 16" Newt. If I have to assemble/disassemble it with each use, I am pretty sure I would choose it often.

 

I agree on both this truss dob remarks.

 

But luckily there is also a collapsible flex tube dob model.

 

Maybe OP should also consider 12" of that model. Not recommendingstrictly my telescope, but this one is still portable on back seat of ANY car and extra easy to setup.

 

And a jump from 8" to 12" is definitely in WOW category.

 

I would suggest to OP to seriously consider 12" collapsibe.

Go for 12 abd WOW yourself. You will not be sorry.waytogo.gif


Edited by Tom_m, 24 April 2017 - 03:03 PM.

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#20 Jon Isaacs

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Posted 25 April 2017 - 05:53 AM

I'm always surprised when this type of question comes up how many posters don't answer, proposing instead a larger scope than what the OP asked for. The same thing happened recently in this post which basicaly asks the same question: https://www.cloudyni...p-in-aperture/ 

 

There is definitely a big difference between an 8 and a 10 inch in terms of what one sees but also in the size and often weight of the instrument. Remember that bulkiness of a telescope increases approximately to the cube of the aperture for a given telescope type and focal ratio. 

 

It is possible to answer the question (which I did) and also address the bigger picture including some of the assumptions made by the original poster.  

 

In the case, the original poster said a 12 inch was too large to transport.  Well, my 12.5 inch takes up considerably less space in the car than my 10 inch F/5 "made in Taiwan by GSO = Zhumell" tube Dob.  It think that's worth pointing out.. 

 

Jon


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#21 Astronought

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Posted 25 April 2017 - 06:19 AM

I have had three dobs - a 10" and two 12"ers.  I found the 10" much easier to use. Not just in transport and set up but at the eyepiece.  So much better handling - like a Lotus over a Bentley.  It got far more use than the 12" ( a excellent Zambutto mirrored scope ), despite the fact that I live at a dark sky site and only have to step off the patio to observe.

However, wether you opt for a 10 or a 12, my main bit of (absolutely free) advice would be to get the best optical sets you can.  The  12" Zambutto mirrored Dob was far superior to the SW / GSO offerings and nowadays it's pretty easy to swap-up either when ordering or later on.

Good hunting!


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#22 Ken83

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Posted 03 May 2017 - 07:57 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.

Same here. And that's what stops me from trussifying (a new word is born) my 16" Newt. If I have to assemble/disassemble it with each use, I am pretty sure I wouldn't choose it often.

Same here I only own an 8 inch currently and will one day jump to a 12 inch solid tube! I think for my personal preference I would not want to setup a truss every time I had to observe. Nor would I want to spend the extra money on the truss style setup and then be forced to buy a shroud on top of that. I'm a true rookie but from what I have read a truss design up to even a 12 inch doesn't seem to be a benefit once you consider the extra steps of setup. In top of that they don't seem to drop weight at all compared to solid tubes as far as I have read on the specs pages of any of the scopes I've looked at. They will definitely be easier to store but at the cost of not wanting to deal with setup? Not worth it. Buy solid tube avoid dew issues and body heat running through the shroud. That's what I have learned from the forums I've read. Obviously far more experienced people out there than me but I've read a lot of what experienced people have to say.
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#23 tommy10

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Posted 03 May 2017 - 10:39 PM

How are your seeing conditions? I live in a LP nightmare, my sky is trash three seasons a year so I got a eight inch and will keep it, the a ten inch is brighter and does better on global clusters but the eight is much lighter and easier to use the f 6 isn't as finicky on collimation , no paracor needed, sharp views, usually the sky conditions limit what is visible on planets and how much detail is revealed in dso, you need to compare the two side by side as the differance is that subtle, keep the eight, save your money or improve the eight with upgrades, imho.

Edited by tommy10, 03 May 2017 - 10:40 PM.

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#24 kkrepps

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Posted 04 May 2017 - 09:44 AM

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".


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#25 gwlee

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Posted 04 May 2017 - 10:43 AM

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. 


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