Balancing a long(-ish) refractor

[gnomus]

I recently got hold of a Vixen 115 refractor.  I'm very happy with the scope, so far, but I would appreciate some advice about how best to set it up and use it.

It only arrived yesterday, and, although it came with rings, there was no dovetail bar.  The black knobs for tightening the rings seemed to rule out a Losmandy plate, so I put an old ~8-9" vixen dovetail on the scope.  From there it was out in the garden to fix it to my Tele Ercole Giro (to which I had added an ADM dual saddle).  

I stuck an ES 20mm 100 degree eyepiece in the diagonal.  To get the scope balanced in this configuration, I had to have the tube WELL forward in relation to the saddle.  Balancing was a bit finicky because of the long length of scope out front.  Nevertheless, I seemed able to get a reasonable horizontal balance, so I had a look at Saturn (which was not all that far above the horizontal!).  I went back and forth with a couple of different eyepieces, but returned to the heavy 20mm at the end and made sure this was in balance.  I thought I'd aim for a much higher altitude object...   As soon as I got to a reasonable amount of altitude, I found the scope was well out of balance again.  Indeed, unchecked it would have spun round at an alarming lick....  I could get balance on the higher elevation, but then I found that it was front heavy as I returned to lower elevations.  Maybe there was something I was missing?

I wonder if I need to get a much longer Vixen dovetail and try to get some counterweight system towards the front (if I am going to keep using the ES 100 degree eyepieces).  Rather than re-inventing the wheel, I thought I might ask around to see what others do.  I am still relatively inexperienced with the Giro Ercole, so absolutely any hints and tips would be welcome.

Thanks in anticipation.

[Moonshane]

To counteract this with a giro  mount you do need to consider a counterweight under the scope in front of the rings.

Stu used to used this.

 

 It's on of the reasons I like my driven eq5 as they are not so sensitive to balance with fracs.

[John]

It can be tricky with the Giro type mounts I found - they do prefer the scope to be kept balanced and thats hard if you use eyepieces that vary a lot in weight.

When I used the Giro II and the Ercole I tended to mount my refractors so that they were slightly front end heavy but I had to remember to tighten the altitude axis tension while changing eyepieces to avoid a sudden nose plunge.

To be honest with you I tended not to use my 2" eyepieces with scopes on those mounts and stuck to 1.25" format ones instead. I largely still do that though I've moved to a Skytee II mount now which has a bit more "sticktion" in the motions.

If you are going to use ES 100 eyepieces only then I think the 20mm will be the one that presents the most challenges. The others in the range are not too different in weight as I recall. Maybe a small counterweight near the focusser end when all but the 20mm are being used to equalise the weight ?

I suspect there is no simple solution to this, just practice to learn what works with your kit, and what does not.

[Stu]

The problem with heavy 2" eyepieces is that they result in quite a lot of weight away from the axis of rotation. This means it is not possible to achieve balance by sliding the scope backwards and forwards in the rings, particularly, as you found, when observing towards the zenith.

I made a contraption which works very well which puts weight under the front of the scope, on the opposite side of the line of the scope to the eyepiece. This counter-balances the eyepiece well enough that the scope will stay in position with the clutches completely loose. You do still have the issue of changing between 1.25" and 2" eyepieces but at least it solves one problem.

I have found that using two scopes somehow balances more easily than one, I think the errors even out a bit more perhaps.

I'll try to find a picture of the thingy I made

EDIT I see that Shane has posted a link to a thread with pictures in already so you get the idea. I have since made a mark II version, similar but with a shorter arm for the weight.

[Peter Drew]

With an alt-azimuth Ercole/Giro type mount you need to try and keep everything symmetrical around the alt axis. The telescope usually naturally  suits this condition once longitudinally balanced but an offset finder or heavy eyepiece in a diagonal will upset things at different elevation positions. 

[gnomus]

Thanks guys for these tips.  I especially liked Stu's contraption.

I am not wedded to the Ercole.  If there is a better solution for my 115 I'd certainly consider it.  I wanted something quick and easy that I could set up on those rare occasions when the imaging is taking care of itself.  I am not sure I can be bothered going through the palaver of setting up and tearing down an EQ mount, but if there was something more appropriate than the Giro ......

Steve

[John]

I find the Skytee II a little better than the Ercole to be honest. I had both together for a while recently and, rather to my surprise, found that the Skytee II handled my largest refractor (130mm F/9.25) a little better than the Ercole did. With my ED120 refractor I don't need a counterweight on the Skytee II. The Skytee II is not as nicely finished as the Ercole and needs at least one of it's dovetail clamps upgrading (the originals are poor) and has quite a different "feel" being stiffer in action but I find it surprisingly effective.

 

[mikeDnight]

Its just a thought Steve, but paulastro mounts his Takahashi FC100DL F9 refractor on an AZ4 and it carries it beautifully. It's lightweight and can be set with just the right amount of friction to stop the scope dropping down when changing eyepieces, yet still glides with gentle pressure. It's a pretty solid mount too! I also used my AZ4 as a grab and go for the last two and a half years and regularly used X296 while observing Mars without issue. Vibration dies down rapidly, 3 seconds or so.

[John]

33 minutes ago, mikeDnight said:

Its just a thought Steve, but paulastro mounts his Takahashi FC100DL F9 refractor on an AZ4 and it carries it beautifully. It's lightweight and can be set with just the right amount of friction to stop the scope dropping down when changing eyepieces, yet still glides with gentle pressure. It's a pretty solid mount too! I also used my AZ4 as a grab and go for the last two and a half years and regularly used X296 while observing Mars without issue. Vibration dies down rapidly, 3 seconds or so.

I'm interested to hear that Mike. I'm looking for a lighter alternative to the Skytee II for my FC-100DL. Good to know that the AZ-4 does the job

[ollypenrice]

What about the Alt/EQ6 in alt az mode?

Olly

[gnomus]

1 minute ago, ollypenrice said:

What about the Alt/EQ6 in alt az mode?

Olly

You don't half enjoy spending other people's money, don't you!!!  

[ollypenrice]

Just now, gnomus said:

You don't half enjoy spending other people's money, don't you!!!  

Enormously!   Not to do so would be to flout the long established culture and tradition of SGL! (OP 1'm looking for a roughly 3 inch refractor in the £300 region. First reply, The TEC 180 would give more light grasp for fainter DSOs and is only just over budget at £18000.)

Olly

[John]

55 minutes ago, ollypenrice said:

Enormously!   Not to do so would be to flout the long established culture and tradition of SGL! (OP 1'm looking for a roughly 3 inch refractor in the £300 region. First reply, The TEC 180 would give more light grasp for fainter DSOs and is only just over budget at £18000.)

Olly

       Spot on Olly !

[gnomus]

Thanks again for the suggestions.  I rigged the scope up again in the house.  This time I left off the finderscope, I stuck a Telrad to the front, and I plunked a plossl in the holder.  The scope balanced pretty near its mid-point.  Furthermore, it felt like I had a reasonable margin of error fore and aft.  The crucial thing is that it held its position, no matter how high or low I pointed it.  

Looks like I should stick with plossls!  I have a longer vixen bar coming so I might be able to add weight (even using Stu's system) if I am tempted to put a heavy eyepiece back in.

[mikeDnight]

20 hours ago, John said:

I'm interested to hear that Mike. I'm looking for a lighter alternative to the Skytee II for my FC-100DL. Good to know that the AZ-4 does the job

May be best to have a chat with paulastro before buying one John. He seems pretty suited with his. 

[paulastro]

22 hours ago, John said:

I'm interested to hear that Mike. I'm looking for a lighter alternative to the Skytee II for my FC-100DL. Good to know that the AZ-4 does the job

Mike is quite right John, in my observatory I use a GP mount, but outside the observatory or for a quick grab and go I use my AZ4.  It works very well indeed.  Of course it does need re-balancing as you go from horizon viewing to the zenith, but this is really extremely easy and trouble free - as is rotating the tube when necessary when using it on my GP.  This has nothing to do with the AZ4, but to do with the ease it can be rebalanced and rotated within the Tak tube clamp.  In my view this is a real godsend, and I wouldn't dream of using it with tube rings.  The bolt on the clamp is large and easy to adjust and the movement of the tube through the clamp as you push it through to rebalance it is smooth as silk with hardly any effort at all, FAR easier than any tube rings I have ever used.  When using it on the GP I can rebalance it and rotate it if necessary in one smooth movement - no problems at all.  As you'll know the tube clamp for the DL is longer than the clamp supplied with the DC and DF which if anything probably makes it even easier.

As Mike says, my AZ4 is extremely smooth also and I can carry it about easily on the tripod.  I original bought the heavier pipe tripod with the AZ4 for greater stability  and, although I still have it,  I  use a lighter tripod with it when using it with the DL as it's sturdy enough and lighter to move around.

If you happened to be at Kelling I'll let you know which pitch I'm on and you'd be welcome to come and put it through its paces and see if it's what you want.

 

 

[John]

Thanks Paul

I've owned an AZ-4 but I've not used one with an F/9 4" frac so it's good so know that it would do the job.