Help Balancing a Short Tube Frac on a Giro Mount

[AdeKing]

I've recently acquired a Giro GR-2 mini (https://www.teleskop-express.de/shop/product_info.php/language/en/info/p1541_Giro-GR-2-mini-Azimutale-Montierung---traegt-bis-4kg-pro-Seite.html) that I was intending to use with my travel scope, a WO ZS66SD (388mm focal length), which I'm having lots of trouble balancing on the Giro GR-2.

The ZS66SD is rather focuser heavy, even with the dew shield extended, and a longer dovetail is attached I can only balance the OTA with a small weight attached to the dovetail.

This works at low to mid elevations but above 45 degrees the weight of the focuser takes over.

I've cobbled together a DIY version of the ADM dovetail counterweight that has the counterweight suspended from the side of the clamp. (https://www.firstlightoptics.com/adm-counterweight-kits/adm-dovetail-side-mounting-counterweight-kit-d-series.html)

However what happens is that the mount balances perfectly with the OTA at a 45 degree angle but moving and releasing the OTA means that the tube swings and settles at a 45 degree angle again.

I've also copied the offset counterweight assembly that @Stu details in this post, and although it's too heavy for the ZS66SD it works well with the ST102 (500mm focal length).

Balancing on the mount is easier with the larger ST102 OTA even without a counterweight.  Does anyone have any tips or should I accept that the pairing of the ZS66SD and Giro GR-2 mini is not meant to be?

[Stu]

That’s annoying Ade. Can you post a few pictures to show exactly how you’ve got it setup?

[AdeKing]

Actually, I've had a play around with it tonight to take some photos and I think that the problem described above occurs when I have the Binoviewers attached with the large offset counterweight assembly that you helped me with Stu.

Here are some photos with my white light assembly comprising the ZS66SD, 1.25" Lunt Wedge, SolSearcher and Lunt 7.1 - 21.5mm zoom (or whatever eyepiece focal lengths it covers), which I've been able to balance successfully tonight by a combination of moving the whole OTA, moving the small counterweight assembly along the length of the dovetail and moving the weight up and down the threaded bar.

Scuse the cuddly toy dog and messy hallway, the latter is a sure sign that I'm in the house or so I'm frequently told ?.

I'll post the BV setup in a bit once I've retrieved them from the garage.

[AdeKing]

Right, I'll be damned if I can't get it to do what it was doing the other day .

Here is the BV setup with the larger counterweight assembly.

I've noticed that balancing is more difficult with the EQ3 counterweight attached to the counterweight shaft.

With this setup I can just balance but it is a but to keen to swing in either direction at the slightest touch.

The Altitude lock seems to be just that and is either completely on or completely off so I can't apply just a little friction.

[AdeKing]

I'm wondering whether it's just a steeper learning curve than I was expecting.

I'm aware that correct balance is needed for Giro type mounts but are they always lively to the touch and eager to swing in any direction.

Maybe I'm just a tad too heavy handed ?

[Stu]

7 hours ago, AdeKing said:

I'm wondering whether it's just a steeper learning curve than I was expecting.

I'm aware that correct balance is needed for Giro type mounts but are they always lively to the touch and eager to swing in any direction.

Maybe I'm just a tad too heavy handed ?

They can be fickle beasts Ade but hopefully you can get to a setup which works for you.

With very precise use of the top lock, can  you control the friction at all? You said not, but I recall when I had a similar mount there was a very small window in the adjustment where it made a different but without locking.

My Giro-WR has a more progressive clutch on it which does help.

Second thing is to pick up on your point about it being harder to balance with the weight on. That is because the weight makes it balanced horizontally and so the axis moves more freely, which reveals any imbalance. So another option might be to move the weight in all the way to unbalance it horizontally and deliberately put a little friction on the alt axis. Hope that makes sense?

[AdeKing]

On 3/28/2018 at 06:23, Stu said:

They can be fickle beasts Ade but hopefully you can get to a setup which works for you.

With very precise use of the top lock, can  you control the friction at all? You said not, but I recall when I had a similar mount there was a very small window in the adjustment where it made a different but without locking.

My Giro-WR has a more progressive clutch on it which does help.

Second thing is to pick up on your point about it being harder to balance with the weight on. That is because the weight makes it balanced horizontally and so the axis moves more freely, which reveals any imbalance. So another option might be to move the weight in all the way to unbalance it horizontally and deliberately put a little friction on the alt axis. Hope that makes sense?

Thanks Stu,

I will investigate the friction lock when I have some spare time over the weekend, you could be right about it being a very narrow adjustment range though, I was expecting something slightly more progressive.  I'll give it another go and see how much adjustment there is, probably only 1-2mm and nearer to the former I suspect.

I have just received a WO EZTouch, which like your Giro-WR does have a more progressive clutch, but its not what I'd call travel friendly.  I will persevere with the Giro-GR2 as I really want to love this setup as its rock steady on my Manfrotto 028 tripod.

With regards to the balancing with the counterweight off, I had a play around and found that there was slightly more friction when the counterweight was right up against the mount and less when the counterweight was at the end of the shaft, I need to weigh the setup to see if its in the weight range for use without a counterweight as I don't want to wreck the bearings.

I'll post back here when I've had a bit more of a play around with it.

Ade