Vixen porta 1

[Robindonne]

Goodmorning.   I was wondering if my grab and wobble mount is to lightweight for my scope.   My only mount for doing some visual enjoyment is a Vixen porta from the first generation. I use it a lot during a week.   Fold it in, walk outside, fold it out and ready to do some observing in 30 seconds.     With an 80mm all works great.  With a 100 mm (and quite longer tube, 900 mm) focusing is a terrible job.  Focus, wait for the wobble to stop, slew to the object that’s already out of view when the wobbling stopped, focus again a bit more etc.  
Is this caused by the mount or the length of the tube?   I realize both are influencing the aftershocks from focusing. But is possible to get a solid grab and go mount that doesn't have this problem?  I see a lot of mouthwatering setups with huge refractors.  Do they all suffer from a period of movement after focusing for example?

[John]

An aluminium tripod does not help. I found the Porta I worked well with my F/6.5 102mm refractor but when I put the 100mm F/9 on it, it was not at all stable. The lenght of the tube makes a lot of difference to stability and vibration due to the lever arm forces that the long tube generates, which put a lot more strain on the mount axis and the tripod hub.

If your 100mm was F/5 the Probably work just fine.

 

[Peter Drew]

I do a lot of telescope mods and use an original Vixen Porta mount for convenience to test for focus, collimation, that sort of thing. I found that replacing the aluminium tripod with an EQ6 steel tripod made a significant improvement with stability.  I just took the legs off the aluminium tripod and bolted the tripod top to the tripod top of the steel one.     🙂

[Robindonne]

2 hours ago, John said:

but when I put the 100mm F/9 on it

Hm ok.   Because you are one the victims who suffer from a mouthwatering setup, how do you use that 100mm f/9?   

40 minutes ago, Peter Drew said:

I do a lot of telescope mods and use an original Vixen Porta mount for convenience to test for focus, collimation, that sort of thing. I found that replacing the aluminium tripod with an EQ6 steel tripod made a significant improvement with stability.  I just took the legs off the aluminium tripod and bolted the tripod top to the tripod top of the steel one.     🙂

I use the old version. The one thats bolted to the tripod with 3 hex screws.  Is that what you mean? Remove that toppart?  Because the porta 2 has something like a removable head, mine only Has a rigorous removable top

Edited July 3, 2020 by Robindonne

[Peter Drew]

21 minutes ago, Robindonne said:

Hm ok.   Because you are one the victims who suffer from a mouthwatering setup, how do you use that 100mm f/9?   

I use the old version. The one thats bolted to the tripod with 3 hex screws.  Is that what you mean? Remove that toppart?  Because the porta 2 has something like a removable head, mine only Has a rigorous removable top

Yes, this is the same Porta mount that I have.  After removing the aluminium legs I drilled and tapped the unserside of the Vixen tripod top 10mm thread to accept a 10mm shaft allowing me to use the tripod spreader of the steel tripod.   🙂

[Robindonne]

9 hours ago, Peter Drew said:

Yes, this is the same Porta mount that I have.  After removing the aluminium legs I drilled and tapped the unserside of the Vixen tripod top 10mm thread to accept a 10mm shaft allowing me to use the tripod spreader of the steel tripod.   🙂

Thx.  Because of your story i got interested in the way the head was mounted to the tripod.  After removing the head i saw a small (shaft) nut that holds the two az parts.  I thightened the nut just a bit more than the markings on the nut showed.  The “wobble” after focusing is reduced, in time, like 80%.   Thx very much for bringing me to removing the head😉

Edited July 3, 2020 by Robindonne

[John]

9 hours ago, Robindonne said:

Hm ok.   Because you are one the victims who suffer from a mouthwatering setup, how do you use that 100mm f/9?   

 

This was some time ago. I don't have either the Porta I or that particular 100mm F/9 now.

The Porta II is designed to be able to move between tripods. I don't think the Porta I was. Sounds like you have improved the situation somewhat though adjustment though ?

 

[Robindonne]

30 minutes ago, John said:

This was some time ago. I don't have either the Porta I or that particular 100mm F/9 now.

The Porta II is designed to be able to move between tripods. I don't think the Porta I was. Sounds like you have improved the situation somewhat though adjustment though ?

 

Oh ok.  So the combo wasn’t a success?   Well i managed to reduce it to almost no movement.  But i dont think i found some great solution for my problem.  I guess i just removed a lot of the movement/backlash grown over time.  Im not sure because my 80 mm didn’t show this wobbling, i might have thightened it more then recommended But is moves smooth even by hand.  So im happy for the moment🙂