Author Topic: Buying big dob, xx14g or xx16g (Another one...)  (Read 33 times)

Patrick Zhu

  • Active Astronomer
  • ***
  • Posts: 111
  • Activity:
    20.67%
  • Reputation: +0/-0
    • View Profile
Buying big dob, xx14g or xx16g (Another one...)
« on: December 24, 2017, 03:57:30 PM »
Hi guys,

So I am planing to purchase either a xx14g or xx16g as my very first large dobsonian.  Currently I've a 70mm refractor (+10 years old bresser skylux(almost unusable due to bad mount) and a 20x80 binocular.  I have been enjoying the wide FOV in my 20x80s the past few months, but today I need something which will make my spouse go "wow" when she sees it (although both me and her love the view from our binos).  I have probably spent about one year on doing research and waiting for the ideal time to purchase a large dob.  Living in Norway means that you won't be outside viewing anything through the summer (the sky gets dim).  So buying one in the upcoming few weeks is your best bet to enjoy it for atleast a few months.  Also locating an active club(let alone one which includes a 14" or a 16" range)is nearly impossible, particularly close to where I reside.  I would love to understand how different the view is via a 14" or 16" compared to my tiny cheap 70mm along with my binos, and if it's close to what I expect (I really wish to see structure about the larger/brighter DSOs, such as the arms of m33, or good detail about m31 etc..)

Anyways, my questions are:
Should I buy the xx14g or the xx16g?
How much more will a xx16g show me within the xx14g in my case?  (see information below in my observing location)
Is there a large difference in how hard it's to collimate a f4.4 vs a f4.6?  (I allready have a Howie Glatter two" laser and two" TuBlug for collimation)

I understand these are large scopes and I understand I shall only be able to see together once or twice a week in maximum (due to work and other stuff and if weather allows it).  So what I need is a range which will give me amazing views the few times I am out observing.The scopes weights aren't really a problem for me (I am 29 and work out nearly every day) and I reside in a home with many storage options (garage, first floor without a stairs to the backyard, etc.).  Also I see that the eyepiece elevation of this xx16g is 72in in zenith.  I am pretty sure that the xx16g used to be a f4.5?  However, Orion's site now claims it's a f4.4.  My height is about 183cm (~72in) so I am only a few cm short of this eyepiece height, but my spouse will definetly have to stand on something to make it to the eyepiece.  How bothersome will it not be able to reach the eyepiece without standing on something?

Some advice:
I have been an astronomy geek as a child, so I understand my nightsky fairly okay (maybe not a problem finding brightest named stars and Polaris, planets etc.), however I really do look at myself as a newcomer in detecting with binos/telescopes.

Observing location will largely be my garden, with a few trips to Bortle class 3 heavens (and even more rarely to a Bortle class two site).  My garden is (according to the light pollution maps) someplace between a Bortle Class 4 and Bortle Class 5 heavens.

I want to largely observe DSO's using the extent, but also get some wonderful detail on planets such as Jupiter and Saturn.

It must be a Goto using monitoring.  I need the observing sessions to really count the few times I am observing.  I have heard from using my binos I can observe an object for a long time and appreciate it, but I don't really like the hunt (or the patience for it).

In general, with no experience with Newtonians and dobsonians, I am trying to find opinion of you guys having the experience.  Are you currently making a good choice?



Ryan Fletcher

  • Active Astronomer
  • ***
  • Posts: 130
  • Activity:
    20.67%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #1 on: December 28, 2017, 10:24:31 AM »
By looking at the Orion telescopes' Specifications pages, you can see that the Limiting (Star) Magnitude forthe Dobsonians is:

Magnitude 15.5 for the 14" size
Magnitude 15.7 for the 16" size

So, there's not a lot of difference there. Compare their "Weight, Fully Assembled":

14" size (per http://www.telescope...s?keyword=xx14g ) = 158 lbs. (71.7 kg)
16" size (per http://www.telescope...ts?keyword=xx16 ) = 195 lbs. (88.5 kg)

... and their cost:

14" size = USD $2,500
16" size = USD $3,500

To me, the Orion XX14g is a better value and is more manageable.

Cesar Rojas

  • Active Astronomer
  • ***
  • Posts: 128
  • Activity:
    29.33%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #2 on: December 28, 2017, 11:02:47 AM »
I agree with Apollo. Also, consider that the FOV is going to be slightly larger with any given eyepiece on the XX14g.Here is a calculator:
http://www.skyandtel...ope-calculator/

I also want tomention the mirror cool down time is also reducedthe smaller themirror.

The benefits of a really large Dob are fully realized under dark skies and since you are coming from a 70mm refractor you might even consider the XT12g (solid tube).You will still have that wow factor and your wifemay only need a small step stool for viewing around zenith. Iwas able to view throughthe XT12g at the Texas Star Party a few years ago and I can say it was impressive. The goto was fast and accurate, but at 5'6" (1.7m) I still needed a single step to view comfortably at zenith.

Oh! I almost forgot, in either scope you mention (with f ratios at 4.4 or 4.6)you will mostprobably need a coma corrector (e.g., Tele Vue Paracorr Type-2) which adds to the complexity and costof viewing, but the XT12g is at f/4.9. You may get away without the coma corrector for most viewing(some are more sensitive than others).

Clear Skies

dustsungline

  • Active Astronomer
  • ***
  • Posts: 113
  • Activity:
    18.67%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #3 on: December 31, 2017, 06:07:36 PM »
I will personally choose 14g over 16g because 1) the extra weight is not worth it comparing to the extra light you will get. 2) $1000 extra is a lot. 3) and the most important reason, at 6 feet tall, I dont need a ladder to go up and down with 14".

Joel Cahill

  • Active Astronomer
  • ***
  • Posts: 116
  • Activity:
    22%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #4 on: January 03, 2018, 10:56:18 AM »
I think you are looking at medium size dobs, lol.

Jairo Zilinskas

  • Active Astronomer
  • ***
  • Posts: 130
  • Activity:
    25.33%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #5 on: January 03, 2018, 10:06:56 PM »
From my experience, given the weight and cost difference, I agree with the others that the 14" is the better choice. I had planned to purchase a 16" scope for my observatory. However, when it came time to order the scope the difference in cost between a 14" and 16" scope, plus the fact that my mount wouldn't carry a 16" scope forced me to purchase a 14" scope.

I amhappy. The 14" scope shows me so much more than my previous 10" scope that I'm amazed every time I view through it. With DSO from my club's dark site I can see objects at least 1.5 magnitudes fainter, perhaps 2 magnitudes (I know, the math doesn't quite work for 2 magnitudes). Favorite objects are so much brighter that I can see more details than ever.

I'm sure I would have gotten a little more of all of that with a 16" scope. But, when making a jump in aperture from 10" I think a 14"-16" scope is a worthwhile step. I now think the next worthwhile step might be 20"-22" (from 14"). That I have no plan for.

micfullprovlo

  • Active Astronomer
  • ***
  • Posts: 114
  • Activity:
    15.33%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #6 on: January 04, 2018, 04:31:02 PM »
Quote
Perhaps have a look at a 20" f3.3.
A 16" is 8" taller than a 14", whereas the 14" likely does not need a step ladder.
The hassle of the 16" is much bigger, but so is that of 14" over 12", and 12" over 10".
10" is not much more hassle than 8". For me 10" is optimal.
But a thin, conical, affordable 20" f3.3 would entice me.

try 24" f3. Is it affordable? probably not to most people. does it entice? absolutely!

This is currently my dream scope. http://webstertelesc...3_Telescope.htm

memeforvi

  • Active Astronomer
  • ***
  • Posts: 117
  • Activity:
    22%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #7 on: January 08, 2018, 01:21:18 AM »
Quote
Quote

Perhaps have a look at a 20" f3.3.
A 16" is 8" taller than a 14", whereas the 14" likely does not need a step ladder.
The hassle of the 16" is much bigger, but so is that of 14" over 12", and 12" over 10".
10" is not much more hassle than 8". For me 10" is optimal.
But a thin, conical, affordable 20" f3.3 would entice me.

try 24" f3. Is it affordable? probably not to most people. does it entice? absolutely!

This is currently my dream scope. http://webstertelesc...3_Telescope.htm
I would really love to get one of those, wow. I'd have to be observing for a while to spend anything in that range. I've set a budget of around 3500$ for my first dob.

I didn't expect that all the opinions would be one-sided towards the 14". So basically the increase in light gathering ability from 14" to 16" is negligible? Isn't the increase in light gathering ability something like 33%?

Bob Meade

  • Active Astronomer
  • ***
  • Posts: 119
  • Activity:
    20%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #8 on: January 09, 2018, 08:31:26 PM »
Quote
I didn't expect that all the opinions would be one-sided towards the 14". So basically the increase in light gathering ability from 14" to 16" is negligible? Isn't the increase in light gathering ability something like 33%?
Maybe not "negligible", but not a terribly important factor. Your perception of light intensity is logarithmic, so a 30.6% (by my calculation) increase in light gathering is a surprisingly subtle difference. That's a real difference, but not a compelling difference.
A "significant" jump in brightness is a bit subjective, but a common rule of thumb for a "wow" difference in visual observing is a 50% increase in aperture is required resulting in over a 100% increase in light gathering. That's a pretty good rule if you're judging about moving from one scope to a larger one and want a "wow", but is perhaps a bit too high of an estimate for your purposes.
A 25% difference in aperture, or about a 50% increase in light gathering, still produces a noticeable difference, for example, but is in the same league of performance. That's about the minimum "significant" difference to me when judging between two different scopes. A 14->16 jump is getting quite minor.
The standards would change if you already had, say, a 12 inch scope. Then the 16inch would be the obvious choice over the 14, assuming the bulk, etc. was OK. But you're moving up from quite small scopes. In the 12inch and over range, you're already well past the "wow" difference and have moved well into the "big leagues". I concur with others that the 12 inch is probably enough to keep you very happy. It'll be a huge jump in performance from where you are now with less hassle. If you're set on something bigger, and worried in any way about the size of the 16inch, then don't hesitate to get the 14 instead.

vicareeti

  • Active Astronomer
  • ***
  • Posts: 122
  • Activity:
    21.33%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #9 on: January 10, 2018, 05:05:26 AM »
Lulz,

I want to again stressthe mirror cool down timeshould be considered as a factor. I see you are in Norway and noted that you said you have many storage options. If one of those options is to store the scopein an unheated location (I would say coolerthan an attached garage) then maybe this isn't an issue, but I image that in Norway even a garage isn't going to be as cool as it is outside after the sun goes down.

You can, of course, place the scope outside and come back in an hour to mitigate this, but the ability of the mirror to cool as quickly as the ambient air cools as the evening progressesis always an issue. Fans can help but still it is something that should be accounted for.

That brings me to wind. If you are in a windy location the larger the scope's profile the more it'll be affected by a breezy night; although, on the plus side your mirror will reach equilibrium more easily .

Finally, aperture fever. It will be much more satisfying to jump from a 12 to a 20+ should you decide to do so in the future. It will be much easier to sell that 12inch scope than it would the 14 or 16.Many people looking for scopes in the 14 to 16 inch range opt for one with premium optics. Use the money you would have spent on a nice set of eyepieces or premium bino viewer.

erenlinra

  • Active Astronomer
  • ***
  • Posts: 133
  • Activity:
    26.67%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #10 on: January 12, 2018, 06:07:04 PM »
Stepping up slowly is a good approach, but will require two or more purchases. I went from an old 8" SCT to an 18" Dob 18 years ago and never looked back and never needed to upgrade. Cool down on the relatively thin mirror is much faster than the old 8" SCT, but is still a factor. The main advantage of stepping up slowly is that since you don't know how you will like the view or inconvenience, a smaller scope lets you more cheaply learn what you really want.

It occurs to me that you can ask the same question 3 ways and get 3 different answers, noting that performance is actually gradually improving with size, but noticing a difference is a threshold and feels discontinuous:

1. Use 14 as a baseline. 16 won't be much different from the 14 visually, but then again a 12 won't be too different from a 14 either, so get the 12.

2. Use 16 as a baseline. 14 won't be too different from 16 but 12 will be different from 16, so get the 14.

3. Use 18 as a baseline. 18 is a great scope, 16 isn't too different from 18, but 14 is different from 18. So get the 16.

George

Ronald Saldana

  • Active Astronomer
  • ***
  • Posts: 116
  • Activity:
    20.67%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #11 on: January 12, 2018, 07:44:51 PM »
Quote
Lulz,

I want to again stressthe mirror cool down timeshould be considered as a factor. I see you are in Norway and noted that you said you have many storage options. If one of those options is to store the scopein an unheated location (I would say coolerthan an attached garage) then maybe this isn't an issue, but I image that in Norway even a garage isn't going to be as cool as it is outside after the sun goes down.

You can, of course, place the scope outside and come back in an hour to mitigate this, but the ability of the mirror to cool as quickly as the ambient air cools as the evening progressesis always an issue. Fans can help but still it is something that should be accounted for.

That brings me to wind. If you are in a windy location the larger the scope's profile the more it'll be affected by a breezy night; although, on the plus side your mirror will reach equilibrium more easily .

Finally, aperture fever. It will be much more satisfying to jump from a 12 to a 20+ should you decide to do so in the future. It will be much easier to sell that 12inch scope than it would the 14 or 16.Many people looking for scopes in the 14 to 16 inch range opt for one with premium optics. Use the money you would have spent on a nice set of eyepieces or premium bino viewer.

Mirror cool down time is something I had "forgotten". How large is the difference in the "cool down time" between the 14" and the 16"?

Bob Meade

  • Active Astronomer
  • ***
  • Posts: 119
  • Activity:
    20%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #12 on: January 13, 2018, 05:36:13 AM »
I've aimed an 18" and watched others do it, with a red dot finder. You really have to know where to aim a scope that large. Finding stuff becomes more difficult. Although, that is what the Ethos is for. But once you find it, the view is better.

neaubigvapec

  • Active Astronomer
  • ***
  • Posts: 118
  • Activity:
    26%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #13 on: January 13, 2018, 06:54:21 AM »
Well, this thread just sold me on getting a 14" instead of a 16" to replace my 10".

Whats that we say? The best scope is the one that gets used? Yeah, I don't want to get into a 16" and be overwhelmed by setup.
If a 14" will give just as good a view as a 16" and give the WOW factor over the 10", then I am sold on the 14".

Thank you all.

galpaydabta

  • Active Astronomer
  • ***
  • Posts: 118
  • Activity:
    24.67%
  • Reputation: +0/-0
    • View Profile
Re: Buying big dob, xx14g or xx16g (Another one...)
« Reply #14 on: January 13, 2018, 11:53:03 PM »
"(I want to see structure on the larger/brighter DSOs, such as the arms of m33, or good detail on m31 etc..)"
Not sure you will get that with a 14 - 16". Good detail on galaxies is hard to get. See the below simulator:
http://www.stelvisio...scope-simulator
On the other hand, nebulas and globs, at a dark site, will really pop! And, hopefully, the optics will be good enough for planets?
The issue I have with those scopes is weight. But if you don't move them much, maybe a nonissue?