8" or 10" Dobsonian? (My first telescope)

[nwink]

Im led to believe that with this kind of aperture diffrence you will only really notice the results of yhe larger aperture in dark skies and low light pollution. I may be wrong tho!

I have heard this before.  Sounds like "Danski Kieve" also agreed with you.  For me, the large majority of my viewing will be in some fairly light polluted skies, since I live in the suburbs.  So with that being the case, maybe going with the 8" would be a better choice for me is I would only notice the larger aperture in much darker skies.

[nwink]

The F/4.7 focal ratio of the 10" will mean that you need to think a little carefully when you come to eyepiece selection, especially if you have a taste for wide field views.

John, could you explain a bit more what you mean in the above quote about eyepiece selection?

[nwink]

Either will be great. About the same size but 10" a bit heavier.

Both will give good views esp from darker skies. Plan for a right ange correct image finder, red dot finder (your neck will thank you for both), a red torch - could be home made, collimation tool and a star map. If this means the 10" is over budget get the 8". Buy used and get it all.

Are there any recommended websites/places to buy quality telescopes used online?  (I live in the States)

[nwink]

Ive been reading too, but not only that, Im sure in one of my threads, sometime back,  I was  also corrected?

My understanding is that all telescopes work at their best under perfect seeing and dark skies, but under light polluted skies,  you will see more with a 10"  or 12" Newtonian than say a 6" or 8"  Newtonian.

Its physics, despite  the atmospheric conditions and light pollution having  the  larger aperture  captures  more, under the same conditions ?

Thats my understanding of having  the larger aperture.

Charic, thank you for your input on the aperture difference being noticeable even under light polluted skies.

[Piero]

The larger is, the more light you will collect, the better you will see DSO.. You can read this on every post regarding a telescope purchase. 

Fair enough, but this is not much of help, to me at least.. 

Instead, think about a typical scenario.. 

How happy would you feel to lift and transport 12-13kg of OTA (only) at least 1.2mt long, four times (house->car, car-> field, field->car, car->house) every time you want to see the sky.. ? 

How happy would you feel to lift and transport at least the same weight for a mount?

To me a hobby is a pleasure, and particularly this hobby should be as much relaxing as possible. If, to you, the points above are not issues, then you should go for a 10in. If those make you think 

more about the effort for doing it rather than the pleasure while seeing, then this suggests that you may not use that telescope very much one day and therefore an 8in would probably be a better choice

Those questions are my *aspirin* for Aperture Fever   

[philipw]

I've got the 8", yes I do wonder if 10" would be better, perhaps size IS everyting. Damn!

[tarotrocola]

John, could you explain a bit more what you mean in the above quote about eyepiece selection?

The lower the focal ratio is, the more noticeable is the coma (distortion) of the image at the edges. With a dobson, is better to have wide fields, so you don't have to move the scope so often, and it is easier not to loose the object during this movement. And this combination, coma free+ wide field, is an expensive combination. Cheap (and no so cheap) wide field eyepieces will show coma at the edge. Anyway, some people tolerates coma better than others, for me is not so bad.

[Piero]

Reading again your original post, I feel I should add other considerations.. 

It seems to me that you haven't really watched through these scopes enough, so if I were you I would join your local association if you can. 

I also think you need to understand the limits of every average telescope.. you will not see like images you can see in internet either with a 8" or 10"... 

It is quite important that you are aware of this 

Said this, and here I might receive bad comments from many people, in my opinion a dobson 8" F6 is not necessarily a good scope for beginners simply because it can be felt as bulky. 

Ok, it is easy to use and relatively general purpose. You can shout a "WOW" when seeing through it, but how long this will last?

Answer: until it gets used.. 

If you watch from your backyard, that can be a good scope. 

However, you might feel it as bulky if you have to carry it around by car... and this depends on your car size and your strength/size..

To be honest, if I were back in 1997 when I started and if I could have afforded, I would have started with a Newton 150 F5 mounted on an Alt/Az mount. 

Something like this: http://www.firstlightoptics.com/reflectors/skywatcher-explorer-150p-az4-mount.html

That is (now) cheap, easy to use, versatile, much more portable (more compact and lighter) than a Dobson 200mm F6. It fits in every car easily and you can even lift easily 

as a combo unit. You add a couple of decent eyepieces (e.g. 25mm, 8mm) and a Barlow 2x and you cover a lot of objects in the sky.

This scope will let you see the Messier objects and many other DSO. True, an 8'' or a 10" will show you more, but for the same reason also a 12" or a 14"..

However, for a beginner, it is important to have something extremely easy which gets used and helps you to develop your skills, and understand your future requirements..

This could be your *training telescope*, which I feel you could use for ages, and the reason is because it is easily portable.

Just an opinion.

Piero 

[nwink]

Reading again your original post, I feel I should add other considerations.. 

It seems to me that you haven't really watched through these scopes enough, so if I were you I would join your local association if you can. 

I also think you need to understand the limits of every average telescope.. you will not see like images you can see in internet either with a 8" or 10"... 

It is quite important that you are aware of this 

Said this, and here I might receive bad comments from many people, in my opinion a dobson 8" F6 is not necessarily a good scope for beginners simply because it can be felt as bulky. 

Ok, it is easy to use and relatively general purpose. You can shout a "WOW" when seeing through it, but how long this will last?

Answer: until it gets used.. 

If you watch from your backyard, that can be a good scope. 

However, you might feel it as bulky if you have to carry it around by car... and this depends on your car size and your strength/size..

To be honest, if I were back in 1997 when I started and if I could have afforded, I would have started with a Newton 150 F5 mounted on an Alt/Az mount. 

Something like this: http://www.firstlightoptics.com/reflectors/skywatcher-explorer-150p-az4-mount.html

That is (now) cheap, easy to use, versatile, much more portable (more compact and lighter) than a Dobson 200mm F6. It fits in every car easily and you can even lift easily 

as a combo unit. You add a couple of decent eyepieces (e.g. 25mm, 8mm) and a Barlow 2x and you cover a lot of objects in the sky.

This scope will let you see the Messier objects and many other DSO. True, an 8'' or a 10" will show you more, but for the same reason also a 12" or a 14"..

However, for a beginner, it is important to have something extremely easy which gets used and helps you to develop your skills, and understand your future requirements..

This could be your *training telescope*, which I feel you could use for ages, and the reason is because it is easily portable.

Just an opinion.

Piero 

Piero,

Thank you for sharing your opinions.  I fully understand that no telescope is going to show me anything like Hubble (which is a massive telescope outside of Earth's atmosphere taking long-exposure photography).  I hope to at least see faint-fuzzies when I'm out at dark sites, and maybe some at home.  I fully plan to attend a local astronomy club when I can, but it's been cloudy here a ton the last couple months around the new moon...and I don't have a lot of freetime for traveling right now in my stage in life.  In the coming year, I should get a little more time for visiting the local club and looking through various scopes, and should get the opportunity to borrow a Dobsonian for a while through the club.  So, those experiences will play the largest in my decision what telescope to buy.  But until then, I'll continue to use my binoculars to learn the sky.

And my thinking is that instead of shelling out a couple hundred dollars on some beginner scope, I'd rather spend some more than that to get a good quality telescope I will use for a long time.  From all the reading I've done...and knowing my primary interest is in observing (not astrophotography), I hear an excellent scope for a beginner is an 8" or 10" Dobsonian on an Alt-Az mount.  That's a little more about my personal background.

[Piero]

Sure, the choice is yours of course, and you know your needs and your situation better than anyone else. 

Mine was just a personal opinion.

I hope that all the answers you collected here helps you make a good choice   

[tarotrocola]

Piero,

Thank you for sharing your opinions.  I fully understand that no telescope is going to show me anything like Hubble (which is a massive telescope outside of Earth's atmosphere taking long-exposure photography).  I hope to at least see faint-fuzzies when I'm out at dark sites, and maybe some at home.  I fully plan to attend a local astronomy club when I can, but it's been cloudy here a ton the last couple months around the new moon...and I don't have a lot of freetime for traveling right now in my stage in life.  In the coming year, I should get a little more time for visiting the local club and looking through various scopes, and should get the opportunity to borrow a Dobsonian for a while through the club.  So, those experiences will play the largest in my decision what telescope to buy.  But until then, I'll continue to use my binoculars to learn the sky.

And my thinking is that instead of shelling out a couple hundred dollars on some beginner scope, I'd rather spend some more than that to get a good quality telescope I will use for a long time.  From all the reading I've done...and knowing my primary interest is in observing (not astrophotography), I hear an excellent scope for a beginner is an 8" or 10" Dobsonian on an Alt-Az mount.  That's a little more about my personal background.

Without freetime, I'd go for the eight, so I can take at any moment 15 minutes to my garden or balcony easily, and you will get almost 15 minutes of observation, because the collimation will hold better than a 10". With an 8" you can see A LOT of things.

[nwink]

I hope that all the answers you collected here helps you make a good choice   

Thank you!  The answers here sure have been helpful for me.

[swamp thing]

 Cheap (and no so cheap) wide field eyepieces will show coma at the edge. Anyway, some people tolerates coma better than others, for me is not so bad.

Not quite.

Often the cheap and not so cheap eyepieces will not show coma as it is hidden by astigmatism in them. The more expensive eyepieces that are better corrected will show coma. Coma is not corrected by any eyepiece only a coma corrector.  it s kinda ironic that as we get better and better eyepiece we see the coma better

[John]

Steve is quite right. Generally coma is a scope generated abberration and astigmatism an eyepiece issue. Some folks can tolerate one but not the other, some folks dislike both and some seem not to mind either too much. 

Mid range wide angle eyepieces might be showing a mixture of both coma and astigmatism !

If you dislike either issue and own a fast scope (say F/5 or faster) investment in a coma corrector and / or better corrected eyepieces will help except for the empty feeling in the wallet area !

[tarotrocola]

Not quite.

Often the cheap and not so cheap eyepieces will not show coma as it is hidden by astigmatism in them. The more expensive eyepieces that are better corrected will show coma. Coma is not corrected by any eyepiece only a coma corrector.  it s kinda ironic that as we get better and better eyepiece we see the coma better

Yes, sorry, I don't know what I was thinking, and I have well corrected and astigmatics eyepieces!

[Sporadic Dobstronomer]

What 16" Dob do you have?  What you've described is a very similar scenario to something I've tossed around in my mind.  Maybe I might get an 8" now for my first telescope...it would always be useful to me since it is a lighter and portable telescope, and it's what I'd use to really learn the night sky.  Then after several years, I could then (if I'd want a larger Dob) do a big upgrade to like a 16".

Hubble-Optics UL16.  Actually about the same weight as my ancient Celestron Ultima 8 but I have had to do things to it.

I have been posting the saga here: http://stargazerslounge.com/topic/229774-hubble-optics-ul16-16-f45-dobsonian-my-experience/

[cotterless45]

Most relevant to choice are considerations such as light pollution and the seeing quality that you're putting up with.

Personally , if you've got average or less conditions , a 8" aperture will suite you fine. F6 will give you enough to get comfortably to x150-200 or down to x50 to enjoy the whole range of wonders in your sky.

Should you be blessed with pristine dark skies, then it's a whole different game and aperture is not only king, but emperor ,

Nick

[Liquid360]

Lol Emperor Aperture.... say it five times fast [emoji6]

[Kropster]

Go for aperture... you can always mask it down to a smaller aperture, but you you can't make it larger!