Mount for ~1m long refractor

[Naemeth]

I'm looking for a suitable mount for my Vixen 80M (910mm) as title suggests after discovering that an AZ-4 isn't really suitable (between about 20 degrees and 70 degrees it slips down to horizontal with anything but a plossl even if the altitude knob is tightened fully).

I was thinking of the Ercole through looking at various options online (seeing what other mounts people use for refractors at around 1m of focal length), and this seems to be suitable, and smooth in use. The high weight capacity is also appealing as it would be very future proof (enough for a 180 Mak and all of my other refractors), and at 3kg may find a way into my travel set-up.

Thoughts?

[moriniboy]

TAL 2 pier, 400mm HEQ5 extension and Skytee 2 on top.

Trouble is it's fixed height so this may cause problems if you get a Newtonian as well.

[Naemeth]

TAL 2 pier, 400mm HEQ5 extension and Skytee 2 on top.

Trouble is it's fixed height so this may cause problems if you get a Newtonian as well.

Indeed it would, is there anywhere I could buy a TAL 2 pier from? I've tried a quick search to no avail.

[John]

A Giro-type mount like the Ercole or a WO Eztouch / AYO type would do the job very well and have a lot of future expansion potential too. The Skytee II would also be another good option with similar capacity. Get a good tripod too like the 2" steel tubed CG5 as it's somewhat taller and much more substantial than an EQ5 / HEQ5 one. Or even a nice Berlebach

I'm just putting the finishing touches to my alt-az arrangements for my 1.9 metre long 6" F/12 refractor and I've had to go up another league again from the above. Grab and go does not come into it - the tripod / mount / pillar alone are topping out at around 90 lbs

[Joseki]

Sorry for the dumb question but isn't the problem with the AZ4 a balancing issue?  Surely if it's balanced properly there shouldn't be significant torque about the Az axis for the altitude knob to stop?  I can see you've got a ton of experience more than me so it's more of a self-centred question as I was vaguely thinking about getting an AZ4 mount sometime in the future for a similar size refractor.  I thought I'd seen review where people happily use the AZ4 for Tal 100rs etc. http://stargazerslounge.com/topic/130942-tal-100rs-first-light-comrades/

cheers,John

[Naemeth]

A Giro-type mount like the Ercole or a WO Eztouch / AYO type would do the job very well and have a lot of future expansion potential too. The Skytee II would also be another good option with similar capacity. Get a good tripod too like the 2" steel tubed CG5 as it's somewhat taller and much more substantial than an EQ5 / HEQ5 one. Or even a nice Berlebach

I'm just putting the finishing touches to my alt-az arrangements for my 1.9 metre long 6" F/12 refractor and I've had to go up another league again from the above. Grab and go does not come into it - the tripod / mount / pillar alone are topping out at around 90 lbs

The budget is really going to depend on how much money I have left after my holiday, and whether or not I get caught by the AP bug on holiday - a Berlebach would be nice but I may have to make do with my EQ-5/HEQ-5 tripod (for now at least).

90lbs, blimey. That makes my 80M look like a paperweight    (it's not exactly the heaviest of things though, perfect for grab and go !)   

[Naemeth]

Sorry for the dumb question but isn't the problem with the AZ4 a balancing issue?  Surely if it's balanced properly there shouldn't be significant torque about the Az axis for the altitude knob to stop?  I can see you've got a ton of experience more than me so it's more of a self-centred question as I was vaguely thinking about getting an AZ4 mount sometime in the future for a similar size refractor.  I thought I'd seen review where people happily use the AZ4 for Tal 100rs etc. http://stargazerslounge.com/topic/130942-tal-100rs-first-light-comrades/

cheers,John

It may be a balance issue - at the moment I've got a short dovetail on there. Perhaps that is the answer .  Will just do some experimenting to see if I can get the OTA properly balanced with a heavier eyepiece through the range of motions.

I wouldn't say I've got a ton of experience - there's still a lot I've got to learn .

[Joseki]

  compared to me you have - and 7 scopes! I'm envious

[Naemeth]

Sorry for the dumb question but isn't the problem with the AZ4 a balancing issue?  Surely if it's balanced properly there shouldn't be significant torque about the Az axis for the altitude knob to stop?  I can see you've got a ton of experience more than me so it's more of a self-centred question as I was vaguely thinking about getting an AZ4 mount sometime in the future for a similar size refractor.  I thought I'd seen review where people happily use the AZ4 for Tal 100rs etc. http://stargazerslounge.com/topic/130942-tal-100rs-first-light-comrades/

cheers,John

You've just saved me quite a lot of money .

Honestly, how could I not have tried that? Just moved the rings closer to the focuser, much smoother now (and considerably less slippage) .

New mount isn't needed after all, but I clearly need to think a bit before jumping in and spending more money .  

[John]

90lbs, blimey. That makes my 80M look like a paperweight     (it's not exactly the heaviest of things though, perfect for grab and go !)   

Thats just the mount - the scope adds another 35 lbs. I'm sure it would sink into the lawn if I put it out there at the moment !

The big issue with these longer tubed scopes is this moment arm force. Basically this magnifies any movement in the tube to the extent that it's makes observing at anything more than low / medium magnification a chore. This is the case even with light weight scopes - it's the tube length that matters.

Goodness knows what it takes to hold a 4" or 6" F/15 steady !

Makes you appreciate ED doublets a bit more. My little Vixen ED102SS at F/6.5 has the color correction of an F/15 but even an AZ-3 will hold it reasonably well and the AZ-4 is rock steady. 

Edit: I do have my tube rings right down by the focuser as well.

[Naemeth]

Okay, after some balancing with my Panoptic I've got the slippage down to about 1-2 degrees when at 50 degrees elevation, which only seems to be when I move up, not down. It worries me that I have to tighten the axis completely in order for it to stay still though, if I loosen it a little it goes worryingly fast towards the tripod.

I guess I'll have to test it more in the field, but it could get annoying in practice unless I stop this slippage, slight as it may be, 2 degrees would lose any target I aimed at from the FOV, but it's a big improvement from a 30-40 degree slippage.

[Moonshane]

The big issue with these longer tubed scopes is this moment arm force. Basically this magnifies any movement in the tube to the extent that it's makes observing at anything more than low / medium magnification a chore. This is the case even with light weight scopes - it's the tube length that matters.

It's also the reason that a well balanced dob is so easy to push about.

[John]

It's also the reason that a well balanced dob is so easy to push about.

Can't argue with that Shane. I guess I'd need a simply massive EQ mount to hold my 12" F/5.3 and yet your simple but well executed plywood dob mount holds the scope steady enough for 400x to be quite practical.

The Giro-type approach is the closest you can get to a dob mount for refractors though. 

[John]

Okay, after some balancing with my Panoptic I've got the slippage down to about 1-2 degrees when at 50 degrees elevation, which only seems to be when I move up, not down. It worries me that I have to tighten the axis completely in order for it to stay still though, if I loosen it a little it goes worryingly fast towards the tripod.

I guess I'll have to test it more in the field, but it could get annoying in practice unless I stop this slippage, slight as it may be, 2 degrees would lose any target I aimed at from the FOV, but it's a big improvement from a 30-40 degree slippage.

I'm trying to work it out, is it nose heavy or tail heavy Jonathan ?

[Moonshane]

Can't argue with that Shane. I guess I'd need a simply massive EQ mount to hold my 12" F/5.3 and yet your simple but well executed plywood dob mount holds the scope steady enough for 400x to be quite practical.

The Giro-type approach is the closest you can get to a dob mount for refractors though. 

I agree John, I really liked the giro mount I had.

[Moonshane]

it sounds like it's still slightly nose heavy?  some people use 'the equaliser' http://stargazerslounge.com/topic/203712-televue-equalizer-2-to125-focuser-adapter/ and others add a small weight at the focuser end, both of which might give a bit more flexibility.

[Naemeth]

I'm trying to work it out, is it nose heavy or tail heavy Jonathan ?

It's tail heavy I believe (the OTA moves down towards the tripod if not tightened up), I've been shifting the rings closer to the focuser to balance this out. I will do some more experimenting now to see if I can get the balance right.

[Naemeth]

Managed to balance - will see if it stays put when using outside.

I definitely under-estimated the importance of where the rings are positioned on the OTA on a long refractor - I will not be making the same mistake again. For anyone considering a refractor at around 1m focal length - keep this in mind. Balance is critical .

[JonF]

It's all about the balance. I use a far bigger frac than that on an AZ4 and it's fine, even using two inch EPs.