GSO F/4 10" CF truss Newt Flex issues

[TrevorW]

I believe the earlier version had an issue with secondary surround flex etc and had to be fixed by reinforcing the secondary surround, is anyone aware whether GSO corrected this issue in later production runs :question::thanx:

[mldee]

I have yet to take a pic with my GSO CF newt, which I bought about 3 years ago from another IIS member, but ready now as soon as the clouds clear. I haven't read much about the GSO truss Newt, they don't seem to be that common. Jeff Lucas on Youtube has a few good videos on it, and based on his video, I rotated the front secondary section 90 degrees so that the imaging train hung vertical rather than at 90 degrees as per a normal optical newt. Simple and recommended to do.

The focuser is attached to a very solid aluminium block, and does not attach to the front tube metal as on most newts. It seems very rigid. I suspect any flex would be in the imaging train components.

I fitted a Moonlight, and as soon as the clouds allow, will try some test pics and post them here.

[TrevorW]

I think I worked out how to get it to hang downward not side ward, how did you go about collimating

thanks :)

[mldee]

I've just tried to find the Youtube video, but no luck so far.

Basically, you just undo the three hex bolts at the truss apexes locking caps on the secondary end and remove the top cap section and truss ball joints, undo the Dovetail which is bolted to the secondary ring, and rotate the ring 90 degrees then do everything back up. It does not fall to pieces:)

I'll continue to search for the video because it's well explained there.

[TrevorW]

oops completely apart oh well good excuse to reinforce the focuser/secondary holder tube :)

[mldee]

Sorry I missed your comment re collimation. I was hoping as it's only an f4 that mightn't be necessary :)

Seriously, haven't even checked it yet, but over the years while building my house/obs, I collected a war chest for that task, including Cheshire, good collimated laser, 2" Barlow, Catseye Collimator set and a dark sky full of stars. I plan on doing initial collimation with the scope at 45 degrees for better eyesight convenience. I can then check using the laser+Barlow if it holds collimation at other angles. News at 11.

I just finished remounting the OTA to the newly polar aligned CEM and rebalancing, so rechecked the mechanics of the secondary mounting to OTA at the same time. It has four 8mm rods connecting the front and rear rings, plus the eight bolts attaching the spider to the front ring plus the 10mm thick focuser mounting plate that bolts to both front and rear secondary rings.

Unless adding more 8mm rods, which would require some relatively precise drilling of attachment holes on the front and rear rings, do you have any other ideas on how to further beef up the secondary section if needed?

[mldee]

Forgot to mention that if my suspicion is correct that the flex is due to imaging train droop as the RA becomes more horizontal, then perhaps fixing a counter weight on the opposite side to the focuser might help. Of course a rigid image train should be the first consideration.

[TrevorW]

In anticipation of needing to maybe do this as a prelude to acquiring the scope I had six 10mm aluminum rods machined and drilled for the job that go around the outside, see attached photos :)

[mldee]

Well done. I wouldn't trust myself to make the rods or holes, but there's a good little engineering shop in nearby Warwick who have done obs work for me in the past, so sounds like a good project for early next year after I've taken a few "before" happy snaps.

By the way, your pics show the process needed for rotating the secondary cell pretty well. Did you bother doing that?

And a lucky last; any idea what the GSO corrector to sensor distance is?

[TrevorW]

Yes I did that as well but not sure where to position it relative to the dovetail plate as at some point while tracking its not going to be downward

[mldee]

Yep, my thinking was just that most of the time (at least for my obs wall clearances) the imaging train would be more vertical than horizontal. As a second minor advantage. the "Home" vertical position slightly reduces chances of bumping it when walking around in the obs. My imaging train will just be the Moonlight CR2, GSO coma corrector, spacers and ASI183MC Pro, and I'll still do your mod next year anyway. Intended main use of the system is to dabble in EAA from the comfort of my living room.
I plan on using the AzEq6 with RC8 or C8 for any mono work, on a separate pier outside the obs. Between focusser, ONAG + guide camera, Filter wheel and spacers and QHY9, it will be prone to droop.

Cheers and season's best.

[DaveNZ]

Not sure if GSO have corrected the issue.

I added some carbon fibre tubes to my 300mm f4 which seems to have worked.