Star Destroyer has landed

[Ags]

I'll let you know. It certainly is a bit annoying, but the vibes do settle down after a couple of seconds. The vibrations are low frequency sways, so I feel the give is in the tube and not the rather stiff dovetail arm (which I would expect to vibrate at a higher frequency).

[Geoff_L]

Thanks. In my case, it seems to be the mount. I mounted the OTA on my EQ5 Pro tonight and it's a completely different animal; steady all the way up to 300x magnification. From this, I've concluded that the 150PDS is possibly undermounted on the Twilight 1. That said, if you get an improvement by spacing the tube rings further apart it'd probably benefit the OTA on any mount and so be a worthwhile upgrade for me also.

Clear skies, Geoff

[Ags]

I did some experiments this morning focused at 125x on a magpie nest. I think tightening the spreader tray really hard makes a difference. After a sharp tap the mount would steady on a count of 20 with no spreader tray, and on a count of 8 with the tray fully tightened. I certainly don't think I have been tightening the tray as much as I should do so i'll pay more attention to this.

Another thing I tried is moving the tube rings closer to the focuser, around the middle of the tube instead of around the center of gravity. The theory is with less give at the focuser, odd touches will put less energy into the system, and it seems to help a bit. Certainly focusing did not seem to cause so much vibration after the adjustment. So I remain hopeful the longer dovetail bar will help a bit.

[Ags]

Had a long look at Jupiter through thin cloud; the air was wonderfully stable but sadly the image was a bit dim. I got to try out my two new toys - the 32cm dovetail bar and the Rigel QuickFinder. The Rigel is absolutely brilliant, it's a great purchase. The outer circle it shows is exactly the same size as the FOV of my 24mm eyepiece, which is pretty neat.

Unfortunately the longer dovetail does not seem to have added any stability and my setup is still Wobble Central. The next thing I'll try are vibration suppression pads. But the vibration is only an annoyance mostly when focusing; the views I'm getting when I'm not touching the scope are superb. 

Later this week I am having a small star party for the new scope with some interested colleagues from work. If the weather holds we will catch the first quarter of the Moon, then Jupiter and maybe some galaxies, if I can find them.

Completely unrelated to the new scope, but tonight we were looking at affordable safaris in Namibia for April next year - 9 nights under desert skies with the milky way at the zenith! Should be amazing if we go, and it gives me enough time to put together my backpackable AP rig - CF tripod, Star Adventurer, modded camera. not sure about what scope to bring - thinking about making an eyepiece adapter for my telephoto lenses...

[Geoff_L]

Thanks for the report. For info, my Twilight I has the wobbles even when only carrying my ST80. However, the wobble amplitude is a lot less and the wobbles dampen out within half a second of me taking my hands off the rig. I get the same order of wobbliness when just tapping the mount or tripod head, so I guess the issue is the mount rather than the OTA. That said, it's still a massive improvement over the Bresser Alt-Az mount it's replacing and the ST80 is usable for visual obs up to its 160x maximum magnification. Perhaps hanging a bag of sand or a waterwedged (i.e. completely full, to avoid free-surface effect) 5 litre water container from the spreader might help.

WRT the lens adapter, they were available a guy named Steven Mogg used to make them until demand slowed down (clicky link) and there are listings on Amazon.co.uk for Kenko Lens2Scope adapters, but these are currently unavailable. Perhaps Astro Buy-Sell et al. have something second hand if you want a ready-made item?

Clear skies, Geoff

[Ags]

Thanks. I think half a second of wobbles are OK, it's hard to get much better than that. 

I tried stacking some bricks on the spreader, that didn't seem to help.

Interestingly, my partner says the new dovetail does make an improvement, so possibly a longer dovetail helps a bit. I'll pick up some vibration suppression pads next.

I've seen Lens2Scope and it is really attractive, but the eyepiece is at the wrong angle for astronomy...

[JOC]

it sounds like you need some sort of dampener.  Rubber is fairly resilient, but it clearly only as resilient than its softness/hardness.  I wonder if sitting each leg on a gel filled pack would provide a more shock absorbing surface?  The sort of gel filled things I am thinking of are cheap things like gel filled shoe insoles or some cheap microwave waterbottles from places like poundland.

 

[Geoff_L]

I attended a dinner/stargazing event last night to celebrate Bodmin Moor being nominated for International Dark Sky Landscape status. I took the Twilight I and ST80 along in case the organizers would welcome an extra tube to spread the load at the stargazing bit. Because there were some children there, I set the tripod up lower than usual -- about half-extended -- and on grass. I'm not sure whether it was the lower height or that it was on grass rather than concrete, but the rig was rock steady all the way up to 80x (any more than that and the targets would have been out of the eyepiece before a couple of people got a look). FWIW, I have a terrestrial version of the ST80, with a fixed dovetail that has some 1/4" / 20 tpi tripod holes. So that the 'scope is the "right way up" (as opposed to lying on its side), I attached a photo ball head to the dovetail plate that came with my EQ5, angled the ball head at 90° and mounted the ST80 to that. With all that potential for flexure, the rig was still rock steady. As you may guess, I'm well pleased!

HTH and clear skies, Geoff

[Ags]

That's interesting information. It looks clearish tonight so I will try to make some improv vibration suppression.

[JOC]

I've remembered where I've seen good stodgy gel filled things that might work - my mouse mat has a getl filled wrist rest - I think the consistency seems ideal for supressing vibrations.

[Ags]

I have some vibration suppression pads arriving tomorrow so we'll see how they work. Failing all else I will pour sand in the tripod legs.

Despite it being a full moon I had my first DSO session tonight and bagged a couple of non-goto Messiers - M3 and M13. I couldn't resolve any stars in M3 but it was a buzz to find it. The conditions were atrocious with only 3 stars in Bootes plainly visible and the Moon glaring into the eyepiece. M13 was a better sight further from the Moon. I also had a long look at Cor Caroli which is a nice double. I'd lined up a few other bright doubles to look at, but with all the glare I couldn't see them.

Earlier in the evening I had a long look at the Moon at 60x with a 13mm hyperion and the detail and color was wonderful.

[Ags]

The vibration pads are a success (I got some generic ones that look like the Celestron ones). My partner declares the view to be "still" and not like "looking at a train speeding past". I would say the vibrations settle in half the time, and I don't pick up traffic tremors any more.

[Stu]

24 minutes ago, Ags said:

The vibration pads are a success (I got some generic ones that look like the Celestron ones). My partner declares the view to be "still" and not like "looking at a train speeding past". I would say the vibrations settle in half the time, and I don't pick up traffic tremors any more.

Good result!  

[Ags]

I was reading on CN that some users have bolted steel plates to the dovetail arm to stiffen it and this reduces vibes significantly. Not sure I would go that far, at any rate vibration pads have solved it for me.

Unfortunately the mount developed a grinding sound in its azimuth axis a couple of weeks ago that got worse over time. So I stripped down the mount this morning to debug and found the small  (6mm?) bolt that holds the azimuth axis in place had loosened causing the axis to tilt and then the head casing ground against the base casing. Continuing the strip down I saw that the azimuth axis is separated by a small black plastic (teflon?) washer with about 3-4cm2 surface area - seems insufficient?

The axis nut is a bit weird (not even an American size apparently) so i had to buy a spanner for the job and after tightening the mount is smooth once again - but I have my doubts the nut will hold. I'm tempted to squirt some nut locking goo on it, but then how would I get into the axis mechanism?

One nice feature is that aside from the weird nut, all other connections in the mount are with the same Allen head size as the Allen key included with the mount.