9 replies to this topic

[GTom]

I am evaluating multiple options which travel mount to use or buy. For airline travel I'd like to get away with as little weight as possible.

As I don't own all the candidates, I am interested if there is a website that already knows the mount specific moment arms?

 

Specifically interested in a gem28 vs SA GTi - 2.8/300nikkor+camera+mini guidescope+focuser combo, approx 5.5kg useful payload, 7cm/3" above the saddle. 

[TOMDEY]

"I am evaluating multiple options ... I'd like to get away with as little weight as possible."

 

Certainly no harm in asking. But, with so many variables involved, I think you're therefore realistically putting the research and analysis burden squarely upon yourself to figure it out. I'd pick my favorite mount for other (performance) reasons... and then just configure and test it well ahead of time at home, using whatever counterweight optimizes performance. Otherwise... it's "tail wagging the dog".   Tom

[speedster]

Both those manufacturers are pretty sketchy with their dimensions and I haven't seen any published dims for those mounts.  The moment arm is simply a distance and you have one on the scope side and another on the counterweight side.  The scope side arm is a fixed distance but not too easily measured although the moment is easily measured.  Even with the mount dimensions, you can't determine the arm length on the scope side. The arm on the counterweight side is infinitely adjustable by varying the weight.  Long arm = less weight.

[Tapio]

If you consider travel mount and weight is important, it's strange that you don't mention SWG mounts.

They are light and you don't need counterweight.

[GTom]

I have been researching them, two issues:

#1: they are expensive. This rig would serve my 2.8/300 telephoto, nothing more.

#2: unguided they have zero chance because of the large, changing PE.

 

 

 

If you consider travel mount and weight is important, it's strange that you don't mention SWG mounts.

They are light and you don't need counterweight.

[Tapio]

There are also cheaper Chinese SWG mounts, comparable to gem28 price.
Not sure you can do unguided with gem28.
And you have mini guidescope in your list.

[GTom]

Yes, I've it, still need a bit of convincing to go down that road. The gem28 I am eyeing at would be a 2nd hand bargain waiting a buyer for quite some time (astro market in the UK is slooow), so not necessarily a bad investment.

 

There are also cheaper Chinese SWG mounts, comparable to gem28 price.
Not sure you can do unguided with gem28.
And you have mini guidescope in your list.

[Der_Pit]

Light counterweight = long arm = more sensitive to oscillations.  So you'd need more stable tripod, and/or wind shielding, dependent on location conditions of course.

 

I've seen 3D-printed (hollow) counterweights that you fill with stones etc. on-site.  Could that be an option?

[GTom]

Indeed, makeshift counterweight ideas are very welcome. Downside is the very low, approx 1/4th density that can be achieved by wet sand compared to iron. Just 5kg/11lbs will be as bulky as a 2L/half gal. juice bottle.

 

Light counterweight = long arm = more sensitive to oscillations.  So you'd need more stable tripod, and/or wind shielding, dependent on location conditions of course.

 

I've seen 3D-printed (hollow) counterweights that you fill with stones etc. on-site.  Could that be an option?

Edited by GTom, 11 September 2024 - 11:59 AM.

[Der_Pit]

Indeed, makeshift counterweight ideas are very welcome. Downside is the very low, approx 1/4th density that can be achieved by wet sand compared to iron. Just 5kg/11lbs will be as bulky as a 2L/half gal. juice bottle.

Yeah, the question is what is more important, weight or volume.  Unless you observe in an area with reserves of uranium ore...   But you can still combine a lower weight fillable one with somewhat larger moment arm, still saves you some kilos.

Something like this?

That one is probably on the large side...