Skywatcher Startravel 120 AZ3 Telescope / eyepieces configuration advice

[vlnikolic]

hello everybody,

 

i would like to buy Skywatcher Startravel 120 AZ3 Telescope, and some additional thingies with it.. i would like to have your advice about eyepieces configurations:

(note: i am aware of that mount is not perfect, and in time i plan to upgrade it)

 

(diagonal mirror would be 2" 99% with adapter for 1.25 ep)

 

configuration1:

ep: 4mm 12mm 20mm (decent quality fov ~65) + decent barlow 2x, thus giving:

4mm+B (300x), 4mm (150x), 12mm+B (100x), 20mm+B (60x), 12mm (50x), 20mm (30x)

 

configuration2:

ep: 4mm 8mm 12mm 20mm (decent quality fov ~65) + decent barlow 2x, thus giving:

4mm (150x), 8mm (75x), 12mm (50x), 20mm (30x)

 

both configurations in conjunction with fringe-killer 1.25 (for eyepieces, and not 2" that could be attached to diag.mirr, as far as i understand) in order to minimize CA

 

this telescope should be used as all-around scope

 

thanks..

: )

 

p.s. idea behind high zoom variants are that i could rely more on the optic, than on my eyes that are not as they used to be..

[Nightspore]

The ST120 is f/5. A spread of eyepiece focal lengths that produce an 0.5mm, 1mm, 2mm, 3mm, 5mm and probably 6 or 7mm exit pupil would be the best option to start with. Although it's basically a rich field scope. A few GSO Plossls are a realistic choice, they are good quality and economically viable.

 

 

A fringe killer won't really be necessary until you approach about a 1mm exit pupil. You'll probably only need it for lunar/planetary observing when the cyan fringing becomes more obvious. At f/5 any eyepiece would have to be relatively well corrected for edge astigmatism (more expensive). 

 

 

I use a 30mm GSO SuperView in my ST80, it doesn't show a huge amount of lateral distortion. The 32mm GSO Kellner (left) does however. Baader Hyperion Aspherics are another good 2" eyepiece and mine get used a lot.

 

 

Exit Pupil = Eyepiece focal length/Telescope Focal ratio 

 

The AZ3 doesn't just have problems, it is incapable of holding any OTA of 80mm or above without significant altitude drift.

 

 

I don't believe it was ever intended for astronomy and only really works as a terrestrial mount.

 

 

Even then the lock-washer isn't strong enough to hold it in the altitude position at any elevation above a few degrees.

 

 

Its main problem, apart from the lock-washer, is that the centre of gravity fulcrum is too far below the centre of gravity of the OTA.

 

 

Furthermore, the aluminium legs are only held in the tripod head by nylon plugs which can often shatter. Mine eventually ended up in a skip. It was never actually used for terrestrial or astronomy. 

 

 

The Sky-Watcher AZ5 or the Vixen Porta II are far better alternatives and actually work properly. Predominantly because of where their centre of gravity fulcrum is positioned. The AZ3 has the efficacy of a chocolate teapot. 

Edited August 5, 2021 by Nightspore

[Marmot]

Hi

I own a Skywatcher ST120 which I am very pleased with. I purchased it (on the used market) combined with a AZ 3 mount/tripod.

The mount has its limitations as Nightspore has mentioned above: The higher you look in the sky (toward the zenith), the harder it is to get the scope to remain in position. The ST 120 is probably at the max weight for the mount so the issue more pronounced than with a lighter scope. The issue is not so noticeable if the angle is decreased, ie Viewing land based targets. There are mods listed on the Net consisting of installing a counterweight, although I have not tried this. The mount got me started, although I soon realised I wanted a replacement, and I have now upgraded to an alternative.

I really like the scope, although it has limitations being F5 (fast). As long as you use it within its abilities It should perform well. It is at its best providing wide views where the magnification is not too great.

Fast Scopes do seem to have a reputation for being a little more demanding on eyepieces and showing up their weaknesses. This seems to be more the case with wide angle eyepieces in particular.

For this reason I have a selection of eyepieces, most of which are fairly average in terms of budget, but don’t have a field of view (FOV) in excess of 60 deg. However, I have a small number of wider FOV eyepieces, but I have ensured that these are of a higher quality (more expensive) in order that they still perform well with a fast scope.

Looking at your eyepiece (ep) configurations I see that your largest  EP is 20mm: An EP larger than 20mm would be a useful ‘finder piece’ to help locate the target. The ST 120 comes with a 26mm (if my memory serves me correctly) and that would probably get you started as a ‘finder piece’.

i have acquired a 32mm GSO (as mentioned above by Nightspore) although mine is labelled Revelation. It makes a great ‘finder’ and also provides wonderful low magnification views.

As for the EPs you chose to obtain, I believe that EPs are quite personal with regard to what is comfortable and works for you and your scope. For this reason I have experimented using the used market in order that I could keep those that suited me and sell on those that didn’t at little or even no loss.

I have only owned my ST120 since the start of the year so my comments are made from the point of view of a relative Novice with limited experience, but I hope that there is something here that is useful to you.

 

[Nightspore]

11 minutes ago, Marmot said:

 

The mount has its limitations as Nightspore has mentioned above: The higher you look in the sky (toward the zenith), the harder it is to get the scope to remain in position. The ST 120 is probably at the max weight for the mount so the issue more pronounced than with a lighter scope. The issue is not so noticeable if the angle is decreased, ie Viewing land based targets. There are mods listed on the Net consisting of installing a counterweight, although I have not tried this. The mount got me started, although I soon realised I wanted a replacement, and I have now upgraded to an alternative.

 

 

 

I think 'limitations' is a more polite plural noun than the term I'd have used lol. I used to talk a lot with a bloke from Vermont who had the Orion version of the AZ3. He spent weeks writing angry emails to Orion about how bad it was. Eventually he took it apart and put some abrasive material on the lock washer. This helped with the friction and he reckoned he fixed it. He was livid with Orion for ages though as they denied it was a problem. I was very disappointed with the 'chocolate teapot', I mean AZ3. I honestly couldn't recommend it to anyone.

[vlnikolic]

hello everybody,

i'll need a few weeks to complete everything i plan concerning this telescope setup.

i'll not speak aloud now about the exact components - but soon you'll find out if i was a good pupil of yours.

thank you!

: )

[Nightspore]

Good luck. I would like to point out that adding a 2" diagonal and eyepiece will add significantly to the overall telescope tube weight and balance. 

 

These are the weights of my 2" diagonals without their 1.25" adapters:

 

Baader Zeiss Amici: 650g

APM Amici: 600g

Altair dielectric: 525g

Tele Vue Everbrite: 455g

Baader Amici: 455g

Baader Dielectric: 425g

Sky-Watcher dielectric: 390g

 

 

With an eyepiece these combined weights can approach a kilo at the focuser end of the scope. Not forgetting the added weight of the finder.
 

Edited August 5, 2021 by Nightspore

[vlnikolic]

hello everybody,

 

since this morning i am owner of beautiful st120.

i have not bought all the equipment yet, but i am very happy.

i have star diagonal 2", 12mm Magellan, 30 mm lacerta ed, and barlow 2x

i am not sure if this lacerta 30 mm is maybe damaged - thus i'll start another formum thread..

 

thank you very much for your help

vlad

[Nightspore]

Congratulations on your new scope. I'm guessing you're talking about a Sky-Watcher StarTravel ST120?

 

 

I have the 102mm version, although there have been several focuser changes, and it now has a MoonLite. A lot of people questioned the sanity of putting a 360 quid focuser on a 170 quid achromat. But it's the largest refractor I can get out relatively rapidly. Any CA isn't really a problem for rich field, DSO's or observing double stars.

 

 

You may find you need a fringe killing filter for lunar/planetary observing. A Wratten yellow or yellow-green filter can be useful.

Edited September 8, 2021 by Nightspore