Goto dob 12 Vs 14 ?

[Stu Ward]

Hi

Seriously considering the purchase of a brand new goto as I'm having little luck in the classifieds.
Now the thing is I have an 8" solid tube standard dob now, and I'm considering either a 12 or 14.

Thing I would like advice on is there $800 worth of value on the 14 over the 12 ?

Whilst the 12 should give me much more than my 8 will I be missing out if j don't get the 14 ?


Thanks

Stu

[DJ N]

Hi Stu,

I have been going through the exact same dilemma. I really had my heart set on the 14, however I have the 12 on order. The biggest deciding factor for me is the size of the base on the 14. The base has a diameter of 775mm and is about 920mm high. This means it will not fit through a standard doorway. I suppose the positive thing about the 14 incher though is the base is designed to be disassembled and reassembled. My only concern is that eventually I would iamgine the nutserts would become sloppy in the particle board. In addition, a number of people who do have the 14 incher, have commented that the base on the 14 cannot really be picked up by 1 person as the handles are too far apart (more so from an ergonomic point of view rather than weight). I suppose the solution to this would be a trolley.

From an aperture perspective of 12 versus 14, from what I have read ( I have never compared 12 versus 14 myself), yes there is a difference at the eyepiece. It is not a wow type factor, but there is a difference.

So in summary, I have the 12 on order. I know I will be always wondering "shoulda gone the 14", but the size and awkwardness of the base really had me concerned. Furthermore, no supplier in Adelaide has the 14 incher setup, therefore could not really have a look at one "in the flesh".



Wish you all the best in your decision!

[madbadgalaxyman]

Let's put some numbers into this discussion......

A 10 inch has 1.56 times the light gathering power of an 8 inch, which is a colossal difference, as we appreciate when trying to see detail on galaxies.

A 12 inch has 1.44 times the light gathering power of a 10 inch. This difference is noticeable to the observer, but it is not
overwhelming.

A 14 inch has 1.36 times the light gathering power of a 12 inch.

In fact, the difference between what you see in a 14 inch and what you see in a 12 inch is not that great;
the level of experience of the observer, the contrast of the optics (e.g. baffling, stray light, and freedom from reflections) , the reflectivity of the mirror coatings, and the quality of the eyepiece, could well make a much bigger difference than the difference in aperture.

In the old "physical size versus aperture dilemma", that is , "I want that extra oomph in my viewing, but can I handle the larger sized instrument?", long experience with owning many and different telescopes taught me the following wise sayings:

The usability of a telescope generally decreases greatly, with increased size. A 10 inch is still "luggable", a 12 inch is a massive brute, and a 14 inch is already an "ultra-brute" when it comes to its size and convenience of use.

The best telescope is the one you actually use, and use a lot.

It's not how big it is that counts , it's what you do with it......

( These opinions are the result of 27 years of regular visual Deep Sky observation )

cheers, madbadgalaxyman

[DJ N]

Makes good sense. I am more and more comfortable with the fact that I have opted for the 12 over the 14. Just makes travelling to dark skies that little bit easier.

Cheers,

Daniel

[Stu Ward]

Thanks for all the comments guys. I reckon a 12 will be my best bet. I reckon I could handle a 14, but the extra effort might be the difference between going out or not on those fringe nights. Also the extra $800 looks could be spent in something else if the 12 is approx x2 my current 8


Stu

[madbadgalaxyman]

I will submit a Spreadsheet (a table), this evening, giving precise numbers for the relative Light Gathering Power (and telescope Magnitude Limit) compared to the relative Telescope Volume (and Telescope Weight), for telescopes of 8, 10, 12, and 14 inches of aperture.

[ obviously, the assumption here is an invariant mount design, a specific optical design and coatings, and a specific tube design(and materials) ]

The Light Gathering Power of a telescope increases a lot when we move from 6 to 8 inches of aperture, and also when we move from 8 to 10 inches of aperture. The L.G.P. gains between 10 and 12 inches of aperture are distinctly smaller but still quite noticeable to the eye.

In contrast, the modest L.G.P. increase that we get when we move from 12 to 14 inches of aperture is swamped by many other Very important factors such as: varying light transmission, varying eyepiece type, different levels of observer skill, etc., etc.

Telescope Volume and Telescope Mass :
These are usability quantifiers (numbers) that inexperienced people do not understand intuitively; even a slight increase in overall Telescope dimensions leads to a significant increase in telescope volume and telescope mass. And your lower back feels the difference!

Nearly every 14 inch telescope is a massive object that is hard to cart around. In fact, for rather a lot of people of middling observer experience, only 10 inches of aperture is about the upper limit for reasonable convenience and fairly easy transport & setup of the instrument.

I will shortly submit some numbers, in order to prove my point.

There have been a lot of terrible 14 inch telescopes around, and a lot of reasonable-to-good 10 inch telescopes around. For instance, many 14 inch Dobs, and also the very old model C14s, have really mushy star images, so some experienced observers actually prefer to look through a 4 inch apochromatic refractor, because of the crispness and contrast of its images. Mechanically and Optically, it is just that much harder to produce a really big Scope that performs well and has reasonable ease-of-use.

We all know a lot of people who own Giant telescopes that lie idle all the time!

[sopticals]

Hi all. I have owned 8" f8 planetary dob better than 1/10 wave pv. A 12" f5 flexitube skywatcher and currently a 14" f5.1 hubbleoptics powered home made dob,(cost of the latter about 2/3s cost of skywatcher). At one time on a night of good seeing all three were set up with two observers and the following was noted: Jupiter 8" and 12" were similar on detail resolved, 14" had a noticable edge on over the others. Moon again not much between 8 and 12, but 14" was in a different class it seemed fine detail resolution was cleaner on small surface luna detail. DSO 14" ruled clearly (made looking through the 8 like looking through dark glasses by comparison) and clearly the 14 showed brighter and better resolution (on for example Tuc 47). So yes a 14 is bigger than a 12 but you do get a bigger brighter picture. Optical quality probably plays a part as well. My 14" Hubbleoptics mirror is rated at better than 1/25 wave front PV.

[Liz]

Good luck for the 12" Stu. :thumbsup:

[Stu Ward]

Quick question about the goto power. Does it come with mains power ? I know that the unit takes d batteries and has a dc adapter in but doors it come with a power lead ?

[Stu Ward]

Anyone know about the power options ?

[Liz]

Hmmm .. not sure Stu, but my little Mak goto uses battery power (i use a power pack from Supercheap), there may be away to convert to mains??

[Red Nine]

Hi Stu,

They don't come with a 12V power lead to plug into the wall unfortunately.

You will need to get a battery pack of some sort (yet something else to add the the growing list of accessories). I ordered mine from Bintel and they recommended their 18Ah Lead Acid Battery, which came with a 12V adapter. It has worked brilliantly so far, I charge it after every viewing session as recommended. They said you'd be able to get around 12 hours out of a full charge or there abouts. It wasn't cheap coming in at $149, but worth the money.

The other alternative is to get a jump start kit from Super Cheap/Repco etc. However, I can't vouch on how well they work, longevity et al.

Hope that helps somewhat :)
Evan

[Stu Ward]

Thanks Red

Bintel Quote this
Power Supply: 10 to 15 V DC 1Amp, 2.1mm Plug (Center positive)

I thought the 2.1mm plug was the female, allowing a mains unit to be plugged into it ?

Is this not the case ?

Would a Celestron Power tank plug into it ?

Thanks

Stu

[Stu Ward]

I was fully committed to buying the 12 goto today. So I turned up at Andrews and they don't stock them at the store. Also some concern is that there is no supplied power option !! You have to buy a battery cell separately. Crazy that it doesn't come supplied with something to at least put batteries in until you invest in a more robust power system.

What are current goto users using for power ?

[Stu Ward]

Look what I just found


http://www.jaycar.com.au/productView.asp?ID=MP3011&CATID=27&form=CAT&SUBCATID=521

[mozzie]

yep stu.. jaycar have heaps of stuff!!!!! how's the scope purchase going....

[Stu Ward]

Badly, as Andrews didnt have stock in their store.
I had the cash in my hand and walked away with it still there !!!!

Stu

[steve000]

most things don't come with batteries.. imagine the cost of 12v worth of D cells VS the cost of a 1/2 decent lead acid and charger.. jaycar has 7ah batterys and charger for about $50.
that will give you about 1.5-2 hours of observing..(ya wanna use about 1/2 the capacity.. my goto uses 2amp)

I made a box with a 12v socket in it packed with 3x these batteries..
http://www.jaycar.com.au/productView.asp?ID=SB2486&CATID=18&form=CAT&SUBCATID=250

I charge them with this connected to
http://www.jaycar.com.au/productView.asp?ID=MB3526&CATID=18&form=CAT&SUBCATID=250

this
http://www.jaycar.com.au/productView.asp?ID=PP1995&CATID=35&form=CAT&SUBCATID=466

pics attached... i pulled out a battery for another project but you get the gist.. there is the risk of running 3 batteries in parallel that the weaker 1 will drain the stronger ones.. i have found as long as you keep them charged the chance for a weaker battery to be created is reduced. I also never use them below 12.4v, battery monitors are cheap on ebay i paid about $6 for mine. or u can just use a multi. there is space under the socket for the charger to store so i always have it.

Alternatively buy a larger single battery.. still keep above 12v tho.
My Goto uses 2amp.. so keeping to the 1/2 usage for a night of observing lets say 6 hours id want around 24amp battery, this will allow your battery to remain in peak condition and last many years.
Sorry for ranting a bit, i love electronics, batteries, power etc.

you could even go an old car battery and charger with the right plugs made up

[Stu Ward]

I didn't expect it to come with batteries included, but to have something to put the batteries in ! That would be nice.

[steve000]

nah unfortunatly no.. i guess to keep weight and simplicity.. 12v of d cells is heavy where as an external pack can be managed better.

A bit of wiring and u will have a decent pack ready to go. just remember to keep it charged and u are good 2 go.

they are also hand for other things, I use it to power my 12v air compressor for the car tyres as well as run some lights etc around the place. great when the power goes out 2. computer fans and leds make good summer cooling and lights when the lights go out.

its also heaps cheaper to make your own.

[Stu Ward]

I've now been informed that andrews don't have stock.

[KenNo2658]

Hi Stu, I use a jump start pack I picked up from Autobarn for around $70. It's designed to jump start a four cylinder car at a cranking amperage of 600 amps. It has a standard 12v cigarette lighter plug that has a steady output of 10 amps if needed. It also has a light that makes packing up very easy. I've used it to power my CPC 8 for around four hours straight without a problem. Just leave it on charge when I'm not using it and grab it and go when I want.
Easy to carry with one hand and fits easily under a tripod.
I think you can get them from any autoparts shop, so it might pay to have a look.
Ken

[ausastronomer]

Hi Stu,

I recommend getting something with a bit more "grunt" than the 7ah. This is really only adequate to power fans and the like on scopes without dew heaters and "goto" capability, IMO. I have 3 power packs for my 14" SDM and 18" Obsession. I have 2 x 17ah packs which will run either scope for 1 nite only and a 32ah pack which will run either scope for 2 nights.

The GOTO drives on the Skywatcher scopes would have a lower current draw than the Servocat Drives on my scopes. I amj alos running 4 dew heaters on my scopes. If you get a jump start power pack with a 17AH battery you will "easily" get one full night and most likely at least two full nights, from this unit. The 17AH packs aren't too heavy and have the added advantage of being able to be recharged from mains power or the car, in addition to having a light inbuilt and a voltmeter to tell you the battery condition.

Cheers,
John B

[Stu Ward]

Thanks for the info guys, what lead do you require from the power box to the dob ?

Any links for where to purchase them would be appreciated

Stu

[Groboz]

Hi Stu

This is my first ever post here so I'll have to properly introduce myself to the community soon elsewhere.

I'm also researching my first serious telescope purchase and have the Sky Watcher 14" flex tube GOTO as my most preferred option. I've lurked here and CN long enough to know what will suit me best and being 6'3, 110kgs and owning a 4x4, I think I could handle something that big. However now that we are finally into our dry season up here, I will be attending some observation nights and speaking to the local experts before I pull the trigger on the purchase.

Anyway, the reason for this reply is that Andrews replied to my query on the 14" yesterday by saying that they are expecting a shipment in 1 to 2 months time. I suspect the 12" telescopes are probably on the same boat. They also stated that they didn't sell the nylon shrouds so I'm going to have to source one from somewhere else.

Good luck with your eventual purchase, I'll be paying particular attention to this thread as like our telescopes..... we're in the same boat.:D

Gino
Darwin

[ausastronomer]

Hi Stu,

In all cases my leads have a male cigarette lighter plug on one end whch goes into the power pack and a 3 pin male din plug on the other end which goes into one of the feet on the powered ground board. It is simple to make up leads to suit your scope. I am not sure what is required for the Skywatcher Scope, but from your comments (I thought the 2.1mm plug was the female, allowing a mains unit to be plugged into it ?) I guess you are going to need a male ciigarette plug on one end for the power pack and a male 2.1mm plug on the other end. All the components you need to make the power cable are available on line from Dick Smith (the shops these days only have computers, TV's and Game consoles), or Jaycar; and its a very easy handyman/solder job to make the necessary cable. If you can't do it, or have a friend that can do it, I would be happy to make the cable for you for the cost of parts and postage. It's a 5 minute job.

Cheers,
John B

[Osirisra]

I use a car Repco 900amp Jumpstart battery pack for both my Meade SCT and my 14" Dob as well as powering the scopes computers it powers my laser finder, DSI cooling fan and skyfi wireless. I can run multiple sessions on both scopes and only ever charge it every now and then. The only way to go in my opinion. Grab a few bits from your local electronics store and or wire up all the cables your self and you are set.

I got a bit of rubber matting from Bunnings that was some type of floor matt that only cost me around 25 bucks. A bit of cutting and some sticky Velcro and it one great light shroud. Just make sure you stitch or add your own glue to the Velcro as it will come off.

[overlord]

LOL Don't worry about it guys, I use a 8" f/5 since 2003 and it's perfect for everything!

[overlord]

BTW, the other things u guys may or may not be considering is that being able to sit down while looking thru the eyepiece adds a pseudo-inch or two to the diameter. Initially I was gonna go for a 10" f/6 Orion but York Optical didn't have it in stock so I went for the 8" They were like the largest available for a decent price back then. So yeah, don't worry too much. in the 80s everyone had a 6" reflector and that was considered pretty decent.

So yeah, I can't imagine sketching without being able to actually sit down, so consider that lol.

[mozzie]

how did you go with melinda's dob for sale stu i see you pm'ed her.there could be a bargain there for you !!!!!!!!

[Stu Ward]

Hoping to do a deal after the Easter weekend

[mozzie]

excellent it's amazing how you miss out earlier in the week and something else turns up a few days later.....

[Stu Ward]

Fingers crossed !

[Stu Ward]

Its all gone a bit quiet on the 14 purchase. I might have to buy that brand new 12 again. Talk about frustrating

[mozzie]

don't rush into it stu...be patient it will fall into place and you'll grab a bargain

[Stu Ward]

It could be a sign, buying a 14 with no warranty.
Daytime demonstration ?

I dont know

Stu

[The_bluester]

Regards the power pack. I am using a 1200A jump starter, no idea how many amp hours it is, but powering my Celestron goto scop by itself it powered it for somewhere near 24 hours before it needed charging. Once I have a dew heater that will obviously reduce but I can not see myself getting less than a full nights observing out of it.

[overlord]

If 14" is ultra brute what is the 25" obsession? I want to get one later this year since I can't find a better planetary solution. It is f/5 btw. :D

[Stu Ward]

I too have abought the same unit, $45 from Super Cheap Auto.
Ran a 3 hour session the other night, and will continue to run it till its out of juice to see what i can get.
This is only running the drives.
No heaters or anything just yet

Stu

[rmcconachy]

Stu, unless your jump starter contains a deep cycle battery (unlikely) you might not want to run it until it is out of juice. Typical larger (not AA, C or D cell type) batteries don't like being drained below about half capacity before recharging. If you do drain them to almost empty the life of the battery may be shortened. Good luck with the big Dob!

[Stu Ward]

Thanks for the advice. Wouldn't want to bugger it up !

Stu

[The_bluester]

I will have to take the back off mine at some point and see what it actually has in it for a battery.

If discharge time becomes an issue I suppose they are cheap enough to buy a second one to run heaters from etc.

[sopticals]

Hi Stu,
having owned at the same time 8", 12", and 14" Dobs and having all set up beside each other going through the sizes quickly sighted on the same objects (whether DSO or solar system) there is a definite improvement in views as aperture increases. And yes the 14" was clearly a step ahead of the 12" (particularly with DSOs).Eventually I quite the 12" but still have an 8" and 14".

In terms of light gathering a 12" collects 2.25x that of the 8".
a 14" collects 3.00x that of the 8".

The 14" gives the real WOW factor. If you can manage it go for 14".

Stephen.

[Stu Ward]

I ended up with the 12 and to be honest I think it's about as big as any one person would want to go unless you have it permanently set up.
The 12 can be moved into position very quickly but she's bloody heavy.

[stevejack]

Sorry I only just saw this Stu or I would have replied last month - I have the 14" GOTO and I think you made a good call with the 12". Not that I regret buying the 14 at all, and I would do it again, but it is hard to get it in and out of the house. And it won't fit in the car without stripping it right down. I have a van to transport it to dark sky sites, but size is certainly a consideration. And it's damn heavy as you say.

I use a 12v car battery with a cigarette lighter plug. I leave the battery on a trickle charger and it's always ready to go. I don't run any extra gear off it (just the GOTO/motors on the scope) and it works great.

Glad you finally got your scope, Enjoy!