Mount Head and Wedge for Astrotrac

[pmlogg]

Tele-Optic has a wedge it calls the ATC for use with the Astrotrac and one of its Giro-mini mounts. The Telescope Express website suggests a 15kg capacity for the wedge, the same as for Astrotrac's own version.

The Giro Mini looks very similar to Astrotrac's own TH3010 head but Tele-Optic puts its capacity at 5kg using the counterweight shaft, i.e half the capacity of the TH3010. Adding to confusion a page on the Telescope Service website suggests up to 9 kg for the Giro Mini.

The Tele-Optic wedge and Mini-Giro are not as pretty as Astrotrac's own but are quite a lot cheaper. So I'm wondering how much I would really lose in capacity going for the Tele-Optic package instead of Astrotrac's?

[m.tweedy]

Will you ever put 15 kg onto it? (That's about the same weight as my "loaded" C11). The biggest scope I have put on is the Megrez 90 and dslr but I have seen Gain lee with a 120 on it.

[pmlogg]

Highly unlikely - I should have made it clear that the question relates to the head capacity not the wedge as both wedges are quoted at 15kg capacity.

What I am really wondering is whether the TH3010 is really capable of carrying twice the load of the Giro Mini or is the difference closer to 1 kg (the 10 claimed by Astrotrac minus the 9 suggested for the Giro Mini by Telescope Service).

5kg might limit possible uses (Megrez 90 tube 3.1kg + Canon EOS Body 0.475kg + any accessories is approaching the 5kg figure and the Megrez 120 alone is 1kg above it) whereas 10kg (let alone 15) probably would not.

[m.tweedy]

to me it is all about the balance. I do not see why the astrotrac head cannot carry the advertised load.

If you live in the North East come round and we can try various combinations (a sort of try before you buy)

[pmlogg]

Michael

That's very kind of you to offer but I'm a bit too far North to drop in. I've bought a 2nd hand Astrotrac from a friend and it came complete with a good quality Manfrotto ball head rated at 6 kg and a Geared Head very similar to the TS Triton, rated at 4kg. The load I'll be putting onto the ball head is probably not more than 3.5kg so I guess its really the geared head which would be overloaded, not it.

Looking again at the Tele-Optic wedge, and the Giro Mini head, I suppose one main disadvantage with them, when compared with the very nice Astrotrac products, is that they are not drilled for the Astrotrac's 3x4mm screws.

[m.tweedy]

Sorry I could not help. I take your point about the screws but the Astrotrac still has the centre screw and screw hole underneath. Also remember the weight on the geared head will be going through the central point and once it is set for your latitude it will not need to be adjusted so should carry the weight easily.

I could not get away with the ball head as there was just too much flex when I had tried to aim the camera it had "drooped".

[garethmob]

When I tried the astrotrac with mine I found it dropped too. For a camera it seemed fine

I'm expecting a az3 in a few days hopefully this would av solved my wedge problems

Sent from my iPhone using Tapatalk

[pmlogg]

Just back from Tromso imaging the Venus Transit using a Giro Mini with twin heads with the Astrotrac on an Astrotrac wedge. I fitted a 2nd shaft collar so that I could move the 25cm long counterweighgshaft back and forth for balancing. On the 2 heads I'd fitted ADM rails to match the clamps I already had fitted to my FS60C in Guide rings and the L-bracket made for the Coronado PST. Both scopes had to be off-set well forward on the rail to balance the weight of the Canon plus TV 2" powermate but I got away with no counterweights. Also added to the system was a home made adapter between the Astrotrac and wedge to allow me to offset the astrotrac by 30 degrees from North pointing. That was needed to prevent the Coronado PST from fouling the Astrotrac when the setup was pointing East at the end of the transit

I'd say that this was on the limit of what the Giro Mini was capable of because even with its Alt and Az knobs tightened very hard to prevent movement I couldn't get it stable enough to fully align the 2 OTAs i.e. the PST would move off target as I adjusted the guide scope rings on the FS60. It was solid enough imaging at short exposures and almost no wind - just adjusting alignment slightly when changing between the two scopes.

The load on the Giro Mini was around 1.4kg at one end and 3.5kg at the other. The heads, collars and rails weigh around 0.6kg each and the shaft .64 kg

The Astrotrac and its wedge seemed fully up to the load and in those conditions the Manfrotto MVB350 and spreader seemed OK. If their had been more wind an even more robust tripod would probably have been preferable.

[m.tweedy]

Glad it worked. Could you post some pictures of the set up as I cannot quite work it out. Just to give me some ideas for mine.

[pmlogg]

Attached is an image of the set-up as used for the Transit.

The wedge was set at 69.4 degrees so the Astrotrac looks very flat. It is offset by 30 degrees by use of the DIY adapter. You can't really make that out so attached is a plan diagramme. It's a bit thicker than necessary but that was the thickness of 75mm diameter aluminium that I was able to source online. One set of 3 holes is countersunk. These are used to attach it to the bottom of the Astrotrac. The others are threaded 4mm for fixing to the wedge. I chose 30 degree spacing but that was arbitrary. I'd worked out that I needed 30 degrees to avoid a collision (or having to refit the Astrotrac to the wedge) during the Transit. TransitSetup.bmp

The central 3/8" hole shown in the diagramme is not needed for this setup but I had in mind the possibility of using the Giro Mini for visual use on the Astrotrac wedge, without the Astrotrac.

Another idea, not implemented, was to make a thick adapter to go between the Giro Mini and the Astrotrac, so as to raise the OTAs high enough to clear the Astrotrac. It would need to be threaded 3/8", and use a grub screw of that diameter to fit the Giro Mini.

The ADM Mini Dovetail System rails on both sides were drilled and countersunk with 6mm through holes to match those in the Giro Mini Heads.

You should just be able to make out the 2 stainless steel shaft collars, one comes with the Giro Mini but the size is standard, OD 34mm from memory, ID 20mm to match the shaft. They are held in place by grub screws, the same diameter as used on the Giro Mini heads. Two shaft collars are needed to be able to move the position of the counterweight shaft for side to side balancing.

What you can't see in the images is that the male 10mm threaded end of the counterweight bar is not threaded onto anything. It is within the Giro Mini head on the FS60C end. You can buy stainless steel rod 20mm OD on Ebay etc that could be used instead of a purpose-made counterweight shaft.

The PST is on a DIY bracket which has an ADM MDS clamp fitted to it to match the ADM rail attached to the Giro Mini head. I use ADM MDS rails on my larger telescopes. That allows the FS60C or the PST to simply be slid on to use for guiding / piggyback. I also have another Alt-Az mount with digital setting circles that has an ADM MDS rail on it to use as a visual grab and go push-to setup with the FS60C.

An alternative to the ADM rails would be to use Vixen ones. If using rails in the way I have solid rails are preferrable to hollowed out ones as you then have full fexibility as to where you drill additional holes. ADM have mostly switched to hollowed out but Anthony Davoli was able to find me a solid bar.

[m.tweedy]

wow very nice thank you

[E621Keith]

Attached is an image of the set-up as used for the Transit.

The wedge was set at 69.4 degrees so the Astrotrac looks very flat. It is offset by 30 degrees by use of the DIY adapter. You can't really make that out so attached is a plan diagramme. It's a bit thicker than necessary but that was the thickness of 75mm diameter aluminium that I was able to source online. One set of 3 holes is countersunk. These are used to attach it to the bottom of the Astrotrac. The others are threaded 4mm for fixing to the wedge. I chose 30 degree spacing but that was arbitrary. I'd worked out that I needed 30 degrees to avoid a collision (or having to refit the Astrotrac to the wedge) during the Transit. TransitSetup.bmp

...

Wow, an alt-az Astrotrac . Nice set up.