8" F6 Strut scope for HEQ5Pro, Worth it?

[Astroman]

Hi all,

Thinking about modifying my current Skywatcher 8" F6 Newtonian into a Strut type scope so I can put it on top of the HEQ5Pro. The idea I have is shown in the image below, simply 4 pieces of 19mm Ply with a Dovetail bar etc.. The idea is so I can modify my current scope that used to go onto my EQ6, but make it lighter for the HEQ5, also without the solid tube should have less momentum force, in theory? I will be using a finderguider so the extra weight shouldn't put me over... Currently I measure the weight of the scope at 7kg. My Refractor and Camera combined is 5kg, so I would like to at least get the weight of the OTA alone down to 5kg if possible... Has anyone accomplished this and how well did it perform? I googled around but didn't have much luck.

The only other thing I may do, since the scope will be slightly shorter for Photography, is I may have to make the Secondary mirror slightly larger to get full illumination.

Image below shows the design with the Rear of the scope towards the left. I haven't added the mirror cell holder or anything like that to the image yet...

[tilbrook@rbe.ne]

Hi Andrew,

That design looks familiar!

I did nearly the same thing to a 4" reflector some years ago. Also made a sliding focuser and secondary assembly too.

I can take a pic and post it if you like?

What I did find that it did end up quite heavy, with the stiff aluminium tube and the plywood was 20mm thick.
Think you would need to consider carbon fibre tubes.

Cheers,

Justin.

[2stroke]

Sky watcher made a f6 8" newt? Its atm why not for fun, lol it wouldn't be worth the hassle money / weight wise but the fun factor wins out. If you were going for for weight i would just rebuild the mount with better bearing's and a full debur/clean/grease.

[Lee]

I always find with these sort of projects, that by the time you've factored in new tools/machinery/materials you'll need, you've spent a fortune, but had fun and learnt a lot...
I can't see much of a weight saving in your plans compared to the steel tube to be honest...

[ZeroID]

Skeletope II was built from the guts ( Mirror, Secondary and Focusser ) of Skeletope I so it could be carried on an EQ6. I got the bare 'OTA' weight down to 11kg and with all accessories loaded it is about 18kg.
I bought a router to cut better circles but they could have been done carefully with my existing jig saw and the rest was just with common hand tools. A lot of the materials, tubes, wood was recovered from scrap being chucked at work (lucky timing with their big clean out I admit). As Lee says it was worth it for the experience if nothing else and it has been a very successful build as far as I am concerned.
The Serrurier truss design eliminates the need for any extra balance weights. The triangular bracing and short tube lengths of the design means you are not using biger diameter tubing to maintain rigidity, Mine was strong enough to stand on end and I could stand on it but it's only using lightweight 20mm alum tube.
Biggest issue is accuracy and care in the design and build to keep it all square and straight.

[asimov]

As you know Andrew, with a bit of planning....You also know I got my 14" SW F4.5 newt down to a tad shy of 16KG to ride the EQ6 - Go for it mate. Not sure about the plan posted though...

[dannat]

Looks similar to the design Dennis Steele of dobstuff uses for his compact dob conversions, I have heard optically the design is fine don't know how you go for imaging,

[Astroman]

I was a little concerned about twist but I think the 160mm x 6mm aluminium plate I was going to use for the dovetail holder would stiffen it up a bit... Quite possible I would throw it overweight using them.

Funny you mention dobstuff, Daniel, that's where I got the idea from.

I am still thinking an f4 ota would probably be easier :-) Might try the f6 on the mount to see how it goes first.

[pjphilli]

Hi Andrew
Weight needs to be watched with the HEQ5 Pro. I loaded mine up to 13.5kg
and ran into problems in this regard. A recent thread gave a consensus
that max loading should not exceed 11-12kg. I trimmed mine back to 11.5kg
and the mount now performs sweetly.
Cheers Peter

[dannat]

andrew here is a slightly diff design -i like the flat panels running down the side rather than tubing -be so much easier to attach dovetail etc