Building an observatory pier

I should mention of course that the material you use to fill the pier is minor in comparison to the diameter, height and stiffness of the pier itself. This should be the main priority by far.

Dave Grennan, That looks like a fine scope, how do you intend to mount it. I'll probabily go for a big trus dob in the next few years, did you ever make up drives for it ?
Would it be feasible to incline the whole thing on a very low wedge and make it polar, you might get some great images with that kind of aperture ?!?

Dave L.

The 16 inch is currently dob mounted. The scope was designed and built by Phil Lardner and I must say Phil builds the best big dobs I know of. I am in the process of installing Mel Bartels homebuilt drive system (have you seen it> If not check it out The biggest problem I'm having is mechanically attaching the stepper motors. Actually attaching them is not the problem. The problem is that the scope is acting like a big amplifier, amplifying the vibration from the steppers. I need to mechanically isolate the steppers so that the vibration doesnt get to the scope assembly at all.
The main problem photographically with this setup is of course, field rotation. Once I get the drive system working properly then I can knock together a field de-rotator. Of course with programs like registax around tracking problems like this can be overcome a lot easier so maybe I wont need the de-rotator at all.

The 12.5inch is mounted on a synta/skywatcher EQ6 mount. See Here for image of 12.5 fully mounted . I may have mentioned in another thread that I plan to replace the drive system on the EQ6 with AWR Tech's EQ6 kit to enable full GOTO and for generally better performance. In the photo you can see the 12.5inch has a split ring system so that the OTA can break in two for easy transport and storage. When I get around to affording the klevzov cassegrain I guess it will also go on the upgraded EQ6. The nice thing about the EQ6 is that its rock solid and has a nice easy release system so that scopes can be interchanged easily.

Dave,
Gosh, the tube looks massive on that mount!, I can see why its giving some problems.
As for the Dob, sounds like you need some sort of dampening ?
How will you mechanically, presumabily physically isolate it, maybe using drive belts ??

Ive read up on field derotaters and they work fine but can be real finicky gadgets to get working right, could you just incline the base of the scope by placing a triange wedge underneath it and then one motor is all you need for tracking, lock the declination axis, and you wont need a field derotater ?!?

Dave,
Gosh, the tube looks massive on that mount!, I can see why its giving some problems.
As for the Dob, sounds like you need some sort of dampening ?
How will you mechanically, presumabily physically isolate it, maybe using drive belts ??

Its not so much that the size/weight of the scope causes problems its more that the standard eq6 drive system is not the best at all. The step sizes in the motors is too big hence there is a detectable vibration at high powers also the whole deal is really only suited to short exposure photography. I plan to invest in a decent CCD camera in the new year and I really wanna be sure that the scope/mount/drive system will be up to the job. As for the dob you are exactly right, belt drives are the way to go. I have gottem hold of some rubbery sef adhesive anti vibration material from a friend of mine and this in conjunction with a belt drive should more than do the job.

Ive read up on field derotaters and they work fine but can be real finicky gadgets to get working right, could you just incline the base of the scope by placing a triange wedge underneath it and then one motor is all you need for tracking, lock the declination axis, and you wont need a field derotater ?!?

Agreed 100% but if you saw the size of the 16inch you'd agree that in its current form inclining it at 53.5 degrees is just not really a goer!!! Also the mirror cell uses a sling to hold it. I'd pretty much have to re-engineer the whole scope to do that. Actually to be really honest I reckon the 12.5inch and perhaps the new 8inch klevzov I mentioned will satisfy my photographic needs. Really the 16inch is just for observing the faintest fuzzys any as I mentioned earlier registax can sort a lot of problems out. Field rotation on the 16inch is really at the end of my astro priorities list.

Clear Skies (Which we havent seen too much of of late:( ),

Dave.

I have been doing a little research myself from whence I started building my 2 scopes, and one thing that was always mentioned but I hardly ever see put to use is that fact that the larger the scope, the closer to the declination axis it should be.

For example, while Dave Grennan's scope looks slightly as if its going to topple over at any moment, if the tube was closer to the polar/declination axis the better. I know that Dave's mount can't do this, as it is factory built, but when building your own mount, this should be taken into consideration. On that mount, it looks like there is about a 8 or 9 inch gap between axis and tube.

If this gap could be brought down to about 2 or 3 inches (which can be done when building your own mount), there is then less need to 'dampen' the scope's movement, as it has a lower center of gravity, and therefore easier to balance, and then manipulate.

One other factor is also to find the tubes center of gravity. This is not always half way down the tube, but should be about 1/3 the distance of the tube from the mirror. This is because of the weight of the tube versus the end weights of a) the focuser, spider/secondary, and finder scope versus b) the mirror and cell.

Just a few things that have helped me in balancing on my mounts!

Seanie.

Agreed 100% but if you saw the size of the 16inch you'd agree that in its current form inclining it at 53.5 degrees is just not really a goer!!!

Clear Skies (Which we havent seen too much of of late:( ),

Dave.

Hi,
Fair enough, I've never owned a big dob and experiance is everything.
It always looks simple until you try it.

as for the weather, its a major bummer