14 replies to this topic

[Paul Skee]

Looking to get a manual Alt/Az for a 102mm F/9.8 achromat. It's the OTA from a Celestron 102 GT. I'm going to gift it to a friend and his wife for their use. I wanted to get something simple, lightweight and easy to use, at the same time offer enough stability so as not to be frustratingly shaky. Both of these are currently "out of stock" just about everywhere I've looked, but there's no hurry. Would either of these be a good choice? Would one be more acceptable than the other. They appear to be pretty comparable in specs? I've looked at the Orion Versa 2, it seems like it's a little less stable, also has no 360 slow motion. Thanks in advance.

Paul

[Sky King]

I can speak for the Twilight I. It's well made and easy to use. Should handle a 102mm no problem. I put my Celestron 4SE on it sometimes.  

[Bean614]

I can speak for the Twilight I. It's well made and easy to use. Should handle a 102mm no problem. I put my Celestron 4SE on it sometimes.  

There's a BIG difference between a 4se, which is very short, and an f/9.8 Refractor,  with a LONG moment arm, and is twice as heavy as a 4se!  I've tried an f/9.8 4" refractor on a Twilight Many times in my life, and it never failed to provide exciting 'shakes', with damping times of 3-5 seconds.

  Go for the Porta-II, hands down! 

[ShaulaB]

We enjoy our Vixen Porta II mount with an 80 mm f6 (480mm focal length) refractor. It is well machined, easy to use, and has great slow motion controls. There is an option of a short or tall tripod to go with it. We have the tall, and it is fine for our needs.

 

Our optical tube is much shorter than yours by half. So I am not sure if your optical tube banging the legs when looking near zenith might happen.

[TOMDEY]

Those might be adequate. I use my Porta II with a 100mm F/5 TeleVue Genesis. Your F/9.8 is twice as long, which could be problematic. You would have to extend the legs all the way up and the focuser would still be quite low when pointing high.    Tom

[Sky King]

The Twlight I is rated to 18 pounds and the Celestron 102 GT is 6 pounds 4 ounces.

[Joe1950]

I have the Porta II. Good mount. But I think the problem with either choice is what Bean614 talks about... the long moment arm effect on such a long refractor. 

 

When you touch the scope, say to focus, it will sway back and forth and take several seconds to stop. It’s a very annoying problem and sometimes requires a rather hefty mount and tripod. Both are important for the stability of the telescope and can be, unfortunately, rather expensive.

 

I had an Explore Scientific 102mm, f/9.8 or there abouts. Nothing I had was really sufficient to stop the shakes until I built a heavy duty pipe mount. It worked great, but the weight of the mount was too much for me to lug outside.

 

Just saying, either of those choices may not be enough to control the ‘moment arm’ sway and using the scope can be problematic.

 

BTW: The amplitude of the moment arm is calculated as increasing by the distance from the balance point squared! So it gets worse very quickly with longer tubes. 

 

Good luck with the choice.

Edited by Joe1950, 08 April 2021 - 05:58 PM.

[erin]

I had that exact scope and used it on my TW1....there were vibrations due to the moment arm and it wasn’t acceptable until I braced the gap in the center of the mount arm. After doing that mod, the damping time is 1 to 2 seconds. Before that, 3 or 4. I love the mount for the slo mo but a scope over 24 inches long (ballpark figure) will give it the shakes.

Edited by erin, 08 April 2021 - 06:22 PM.

[Bean614]

The Twlight I is rated to 18 pounds and the Celestron 102 GT is 6 pounds 4 ounces.

It's not just the weight!  It's the weight combined with the moment arm!  18 pounds, on a scope 12 inches long, would be fine.

[teashea]

Looking to get a manual Alt/Az for a 102mm F/9.8 achromat. It's the OTA from a Celestron 102 GT. I'm going to gift it to a friend and his wife for their use. I wanted to get something simple, lightweight and easy to use, at the same time offer enough stability so as not to be frustratingly shaky. Both of these are currently "out of stock" just about everywhere I've looked, but there's no hurry. Would either of these be a good choice? Would one be more acceptable than the other. They appear to be pretty comparable in specs? I've looked at the Orion Versa 2, it seems like it's a little less stable, also has no 360 slow motion. Thanks in advance.

Paul

I can speak highly of the Porta II.  I have five of them.  The design, build and finish quality are excellent.  Although Vixen says the capacity is 20 pounds I would never put more than half than on one.  Remember that the mount is more important than the telescope.  So many people undermount their telescopes - and that creates much unpleasantness.  

 

 

[Jon Isaacs]

The Twlight I is rated to 18 pounds and the Celestron 102 GT is 6 pounds 4 ounces.

 

I have both a Portamount and a Twilight 1.  The ratings have no meaning. I consider the TW1 adequate for a 6-7 lb 80 mm F/7 but for a 4 inch F/10 with its long OTA, Bean is on the money, it's a shaker.. 

 

Jon

[Paul Skee]

Thanks everyone for your input. I believe I'll go for the Vixen. I put myself on the waitlist at a couple of vendors. Also check the classifieds from time to time. My friends have a vacation home out near Bullhead City, Arizona. I've been out there, it's about Bortle 4. They are not what I'd consider to be avid enthusiasts, they are going to be happy with something they can carry out to the backyard patio, point it up to the moon or whatever planet might be up, look in the eyepiece for a minute, then go back inside. But you never know, I want to get them something that won't be so frustrating as to desuade any possibility for advancing an interest.

Thanks again,

Paul

[Robindonne]

I have had the porta, porta 2 and my recently bought gso mount.  A very easy side by side comparison having both side by side. the winner on all fronts is that gso.
The gso’s arm is adjustable and shows no flex like the porta arm.

The dampingtime for both a mak127 and a 120 ed is much shorter on that gso.

The slomo control knobs on the portas are plastic vs solid alu ones on that gso.  Be aware when buying longer slomo cables, the porta connection is a 6 mm vs the gso 8 mm

The porta 2 tripod is weaker than the porta 1, both connections of the thin alu legs are made from plastics, but can be upgraded with a Vixen Hal tripod for example.

 

I think that gso is a very underrated but well build alt az mount and comes standard with this Hal tripod.

The Gso’s price is almost the same as just that Vixen Hal tripod upgrade for the porta mount.

In the US its probably also sold under another brand, not sure which brand!
 

In general the tripod makes or brakes the mount setup.

 

The porta’s are both sold but i remember i wanted to swap the (allen key) tension screws on the portas for more easy adjustable screws. The gso comes standard with a solid thumb screw on both axes!

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Edited by Robindonne, 09 April 2021 - 06:55 PM.

[BlueMoon]

+1 Porta II. I use it with the Tall+ tripod and frequently with a SW 72ED scope. I recently disassembled both alt and az rotators (winter, cold, snowing, miserable, bored) and tuned them up. Cleaned, greased and adjusted the gear mesh a bit looser to my liking. They are very easy to work on if one desires it.

 

Excellent rig for lighter scopes with damping < 1sec for me. It handles my SW100ED APO @ 11 lbs okay but with a longer moment arm (36" scope") the damping suffers at higher mags. Sure can't beat them for being trouble-free. 

 

Clear skies. 

[Paul Skee]

Robindonne, thanks for the tip. According to info from the Agena site, the GSO SkyView Deluxe may be a contender. However, there is no indication that it will come back into production. This has prompted another search which resulted in a look at the Astro-Tech Voyager 2, also one to consider. I looked at the TPO Alt/Az that OPT has. It looks good also but is a little more than I want to spend. Anyway, as I said, there's really no rush. Would just like to get them set before spring comes to an end. Thanks to all.

Edited by Paul Skee, 10 April 2021 - 10:35 AM.