Motor or not

expon (Jas) · #1 15-03-2014, 08:19 AM

Hi,

Last Saturday the sky was clear over Melbourne. In fact it was as clear as I had ever seen it (im new to this so im sure there has been better). I grabbed my recently aquired 90mm refractor and was able to see Saturn and its rings quite clearly. This was from a place 5km from the CDB, I was pleasently surprised. Anyway I showed my wife and she thought it was nerdy but after convincing her to look she was only concerned that it was so tiny and it was moving too fast.

I wanted to buy a dobsonian scope, I have been looking at a 10" but recently have been leaning towards an 8" as most of the time I will be within city limits and it's much easier to move an 8 than a 10. But my wifes comments got me thinking about a tracking scope to follow objects. I quite like the idea of finding stuff myself however when the city lights are affecting vision that might prove more difficult.

Are dobosnian scopes a right pain in the butt to use when following something moving so fast? would a motorised tracking scope be better? Keeping in mind my wife cannot use a remote control properly so I dont think she would be too good at tweaking the controls to follow an object manually.

Am I better off going with an eq mount with motor? I am not interested in astrophotography (yet) but I do have a nice slr camera. I prefer to marvel at the sights and wonder, I don't need to photograph it.

As a second question are refractors better than reflectors? I understand the price goes through the roof however what kind of difference would there be between say a 5" refractor and an 8" reflector?

Thanks very much for all input.

glend (Glen) · #2 15-03-2014, 08:40 AM

The Alt/Azimuth mounts are the easiest to use in my opinion, and simple compss and altitude devicrs are available to assist locating objects. Dobonsian scopes are good starter scopes and pretty intuitive to use but as they get larger they get heavy and require more space to store etc. Dobsonians are also the least costly per inch of aperture. Suggest you go to Bintel and talk to them and look at scopes. Personally I would stay away from goto or motor driven scopes initially as they are expensive compared to the same manual scope and you will not learn the sky as quickly IMHO.

2stroke (Jay) · #3 15-03-2014, 09:11 AM

Comes down to your budget and you can't beat a newt dob for bang for buck. If i was to buy a first scope and had the money it would be a goto 8" dob, if really tight for cash or not sure on the hobby a 6" dob, then a 8". I wouldn't start with a 10" again because moving it about can be a turn off as a beginner, yer the first few weeks your all over it but then you start thinking can i be bothered lifting this thing out side. My wife has a 12" goto dob for planetary and pub viewing nights, why the views are unreal it's something she never really uses around the home because of size and weight. The best scope we had was the 6" dob and now we plan to get another because it's so quick, light and easy to use. I mean with a 6" you can be watching tv and then just go i might take a peek pick the thing up with your eye piece case and be straight into it.

cometcatcher (Kevin) · #4 15-03-2014, 09:12 AM

What sort of mount is your 90mm refractor on now? If you are not sure do you have a photo?

expon (Jas) · #5 15-03-2014, 09:40 AM

I'm pretty sure it's alt azimuth but i'll post a pic when I get home. I got it from a friend of a friend who was moving overseas. From memory it's the saxon 909AZ3. I do find with this scope that when focusing the scope shakes like mad (that or my hands shake too much).

The tracking aspect of motorised scopes is what really has me interested.

I have heard that there wouldn't be much difference in getting a larger scope (10" over 6") in areas with high light pollution as the conditions are not good enough to take full advantage of the scopes capabilities.

cometcatcher (Kevin) · #6 15-03-2014, 10:11 AM

Depends what you want to view. Light pollution has no impact on planets, only DSO's.

Okay 909AZ3 is the alt/az mount. You could put your present scope on an EQ mount but it would cost at least a few hundred dollars to do so. That would be a non goto, just an RA drive on an EQ2 which are still wobbly. A good goto mount like the HEQ5 pro is about $1200. That wouldn't wobble with your 90mm refractor.

EQ mounts need polar aligning to track accurately. For visual use rough setup would be fine.

My take on big dobs, they are great for DSO's where low power is used. High power for planets, the planet zips through the field pretty fast. I always found this to be annoying unless the bearings are really smooth. For planets I like tracking. DSO's I don't care.

It depends how much money you want to put into it. This hobby can be a bottomless pit if you're not careful.

julianh72 (Julian) · #7 15-03-2014, 11:09 AM

A relative newbie's perspective :

My perfect telescope would have 10" plus Aperture, a computerised GOTO self-polar-aligning Equatorial mount, would collapse to easily fit into the boot of a small car, would weigh no more than about 20 kg (including the carry case), and would cost about $1k to $2k.

(If anyone knows where I can buy one of these, please let me know!)

Apart from that, we have to make compromises, and I recently bought a second hand 90 mm short tube refractor on a lightweight (but reasonably sturdy) Equatorial mount as my "Go anywhere" scope for when I can't get to my Dad's 8" GoTo SCT.

A lot of people recommend simple Alt-Az mounts for small telescopes for beginners, and I can certainly understand this, because anyone can easily understand how to set up and point an Alt-Az. However, I like an EQ mount. I don't have any trouble doing a rough polar alignment for visual use, and I also understand how to deal with the "gimbal lock" effect you can get when the scope is in some orientations. (Prior experience with EQ mounts, and an Engineer's brain, might help here, of course!)

The killer for me is that even with a quick rough initial alignment, you can easily track your target with only the occasional twist of the single RA slow-motion control. I don't know if it's just me, but on an Alt-Az mount with slow motion controls, I always seem to turn both controls the wrong way before I track the right way. (It's a bit like how logic would say you have a 50:50 chance of inserting a USB plug the right way on your first attempt, but in reality, you get it wrong 99% of the time!)

And of course, with an RA motor drive on an EQ mount, you can follow your target for quite a few minutes without any adjustments. (Now, if I could just find a suitable drive for my non-standard EQ mount... But that's another story.)

jenchris (Jennifer) · #8 15-03-2014, 12:13 PM

To be honest, I wouldn't look at a DOB as long as there's flies inthe outback (but not for that reason)
They're long and bulky once you get over 6" - they seem to need more car space than my LX90 because the base is so big - the base is made of weetbix wood and is devoid of marking so you have to guess until you've made a circle gauge.
My SCT is F10 2000mm and, on a wedge, takes passable piccies which I can impress the rellies with. It guides well if it is set up properly.
It 'goes to' even when it is cloudy so I can do a cloud dodge night if I want to see something - impossible with a DOB.
But - there's always oneof them isn't there?... they are more expensive than a DOB - by quite a margin

colls (Michael) · #9 15-03-2014, 12:58 PM

I have a ED120 refractor on a EQ5 converted to a Alt Az mount and works well for me.

doppler (Rick) · #10 16-03-2014, 01:31 AM

Quote:

Originally Posted by julianh72

A relative newbie's perspective :

I also understand how to deal with the "gimbal lock" effect you can get when the scope is in some orientations. (Prior experience with EQ mounts, and an Engineer's brain, might help here, of course!)

I have a 70's 8" newt on a eq pier mount that has a tube rotation mounting ring system so I can just spin the tube to a good eye piece veiwing position. It has adjustable tension bolts with teflon tips on the rotation system but I have only had to adjust them a couple of times in the past 20 years. I really dont know why they stopped making them.

Forgey (Paula) · #11 16-03-2014, 02:26 AM

Hi Dys, how much are you looking at spending?
For a Dob and 8" goto tracking dob is going to be about $1200-$1400.
A non goto tracking 8" dob you be looking at between $500-$700.
Those prices depends on where you purchase from. (Bintel or Andrews communication) and if its a collapsible dob.
I have a 12" goto dob and I love it, apart from the weight.

barx1963 (Malcolm) · #12 16-03-2014, 02:09 PM

The obvious comment to make is that there is no perfect scope, if there was that would be what everyone would use. And human nature being what it is, once people make a decision on a scope type, they will tend to defend that decision, often ferociously!!
So the task is to make a decision based upon what you want to achieve, what your budget is and your future ambitions.
Dobs are popular because they represent the best way to get lots of aperture at a lower outlay of $$$. The tracking dobs I have seen when setup properly track very well. As Jennifer has stated a go to SCT is compact and very capable at tracking but involves more dollars per inch.
EQ mounted scopes tend not to have the big apertures but can both track and take care of field rotation, but can be daunting for beginners to setup and basic ones without go to are not as instinctive to use as an alt az mounted scope.
Beginners often get confused over whether simply tracking is sufficient for imaging use, so if you intend going into imaging, you may find that a tracking alt az acope (motorised dob or fork mounted SCT for example) is limited for that purpose and an EQ mounted scope is a better option.
As far as dobs go and the movemnt of objects in the field is concerned, I have used dobs for years now and to me it is not really a hassle. A well built dob is easy to move and the view settled down very quickly.

Malcolm

expon (Jas) · #13 16-03-2014, 02:17 PM

Thanks very much for the replies here. It's certainly food for thought.

The motor adds a significantly large amount to the price that I could be spending on a better scope. In the beginning I want to keep it below $900 as I am not to convinced I will head out of town to avoid the light pollution.

I like the views with the 90mm refractor I have but I have difficulty really seeing much more than a large dot in most cases. I did see Saturn and was amazed, it really was indescribable. However jupiter was just a muddy ball but I could see the 4 moons as specs of light around it. I would like to see more detail so I am not sure if it's aperature I need or perhaps better quality optics?

barx1963 (Malcolm) · #14 16-03-2014, 02:37 PM

Jupiter is very low this apparition for southern hemisphere observers which means it is badly affected by atmospherics, Saturn and Mars should be very nice this time around as evidenced by the quality of the images being presented here on IIS.
Clear views of bright objects like planets can be obtained in a number of ways. I have used dobs mainly as mentioned earlier and aperture is definitely an advantage. Last March I had my first good look at Saturn with my 20" and the memory of it is burned into my brain. The Cassini division in the rings looked like it had been drawn with a black texta and there were moments when the Encke div was clearly visible. In my old 12" the Cassini was only occasionally glimpsed. Aperture allows you to push the magnification higher to really take advantage of the seeing when it is at its best.

Malcolm

expon (Jas) · #15 16-03-2014, 02:53 PM

Thanks Malcolm

How would you suggest that quality of the optics affects things? Would a premium brand 80mm be better than say a skywatcher 90mm? A significant difference?

cometcatcher (Kevin) · #16 16-03-2014, 02:59 PM

To add what Malcolm has said, seeing is important. A 90mm refractor is capable of excellent planetary views, but there are a few do's and don'ts to follow. Do observer when the planet is as high as possible in the sky. The less murkosphere to look through the better. Don't observe over a hot road, roof, driveway or parking lot after sunset. The heat shimmering will kill any detail present. A grassy field is best but even these can produce thermals if hot enough.

astro744 · #17 17-03-2014, 01:12 PM

Quote:

Originally Posted by expon

Thanks Malcolm

How would you suggest that quality of the optics affects things? Would a premium brand 80mm be better than say a skywatcher 90mm? A significant difference?

A telescope with premium optics will definitely be an advantage. The optical design is also important and a telescope designed to give colour free images (i.e. all colours focus very closely together) whether it be an APO triplet or ED doublet is will provide much better views especially at higher powers. Such telescopes will out perform any short achromatic refractor under f15 (and perhaps over). Of course the telescope too has to be made by a reputable dealer and preferably hand crafted or at least be hand inspected during any quality control process. (Tele Vue comes to mind here)

Collimation too is critical for a good image with any telescope and most refractors need no tweaking whereas Newtonian reflectors need to be checked often.

If you are considering a DOB you can get a Poncet Platform to enable tracking for up to 1 hour before having to reset the base (a mechanical function). Search the web for Poncet Platform and you will get some images. Such a platform provides EQ movement not Alt-Az movement and therefore you wont have the field rotation issue provided your platform is built to the right latitude.

See http://www.equatorialplatforms.com/ for platforms by Tom Osypowski.

Having an image that does not move is a definite advantage as one can then concentrate on seeing subtle detail and such detail is then much easier to see since you are not shifting your attention on a moving object. This is as much true for observing planets as it is for observing faint galaxies.

Note too you want a solid and stable mount/platform as any wobble of the tube on its mount during observing can also take your concentration away from the object especially at high powers.