Piero

Hi Paul, the big difference was due to the lack of cable sling. The fan helps this telescope cool down and keep constant temperature very well in my opinion. I believe this is due to the wood structure and the mirror cell that is not much exposed. In a split tube dobsonian, possibly the fan is less effective, but I don't have experience with this really. The new Antares finder works really well. Thank you for the suggestion. As I said previously, the longer dew shield is certainly an advantage in delaying dew formation. I could easily spot M15 as well as other DSOs in the finder directly.

It was just a dot, but I could see it with DV once the scope cooled down properly. I don't know the exact magnification as I used a zoom eyepiece, but this was somewhere between 240x ish and 273x.

Great report! Saturn was wonderful last night and the seeing was reasonably good here too. Enceladus was visible in my new dob. Nice one!

I would also consider the SLV as Louis suggested. Great eyepiece!

Thanks Jeremy! it worked really well last night.

Last night the sky was good here in Cambridge. I took the telescope out quite late (at about 11pm). After a couple of collimation rounds, I pointed at Saturn. For the whole session, the fan was on. It was incredible how Saturn was getting better and better at the eyepiece as soon as the mirror was cooling down. Seriously, the improvement was observable. After about 15 minutes, Saturn was showing some lovely details. The Cassini division was visible almost all over the rings. To be honest, it wasn't just visible, it was a nice black lane. In the lateral part of the rings ("wings"), some differences in contrast were also detectable. The planet showed a nice and distinct equatorial belt with again faint differences in colour in the north hemisphere. For sure, the visible moons were: Titan, Dione, Rhea, Encelados, and Thetys. These were checked with the Sky and Telescope website. However, there were a few other "objects" which were not so dissimilar from those moons. Without a map for those, I cannot confirm whether they were faint stars or some of them was a moon. After Saturn, I observed M15, Double Cluster, NGC 7331 (C30 - galaxy in Pegasus), and one of my favourite open cluster: NGC 457 (Cassiopeia). It was the first time I observed these targets with this aperture. Absolutely impressive views. Very happy about this. --- Astigmatism? A memory of the past! Removing the sling really solved that issue. New finder works nicely. I particularly like its long dew shield and the fact that I can rotate the eyepiece.

The new finder arrived! I didn't know it was so versatile. Out of curiosity, I swapped the RACI prism with my TV everbrite diagonal and 24 Pan. It reached focus without any issue using the helical focuser near the objective! I tried in daytime and optically speaking, it seems excellent for a sub F4 acromat refractor. I'm curious to test how much magnification this finder can take... This will be the finder for both my Dobson and Tak, as I plan to attach it to the other arm of my Aok Ayo2.

What a difficult question! Probably the new dob I've got! If something smaller, it would be a 12 f4 or a 10 f5 both with coma corrector.

Good question. In my opinion, the way it was installed would have caused astigmatism independently of any adjustment. In my limited knowledge about this, a requirement for a sling to work correctly is that it must be parallel to the mirror plane. This is the basis. Then there are different configurations as Gerry showed some post above (e.g. 180 Deg, 90 deg..). In my case the sling was passing through the two mirror edge supports which are attached to the mirror cell and don't necessarily follow the mirror plane at different altitudes. Therefore when the telescope changed altitudes, those supports tightened the sling which eventually sequeezed the mirror edge, causing astigmatism. To work, the sling should have been detached by those supports and a gap of a few mm should have been left between sling and edge/bearing. I could have done this, but didn't want to risk with other potential problems related to the sling that I haven't yet foreseen. Knowing that it was not required for the correct functioning of this telescope, I thought it was safer to simply use the current edge supports and remove the sling.

Mine wasn't as sharp on-axis as the docter. Instead it was more similar to the SLV.

Fair point, John. I should have been more precise. I didn't mean that the BCO is not good, but simply that the one I had was not at the level of my Docter UWA. As this similarly was detailed a few posts above, I simply infer that there could be some differences between BCO units. My previous SLV 9mm was close to the BCO I had. Between the two I prefer the SLV due to the larger frontal lens and longer eye relief.

With a short tube like the 72mm ed I would not barlow but get the eyepiece. The 10mm BCO was good but didn't impress me. It wasn't on par with my Docter but it was close to the 9mm Vixen SLV I had. I believe that there is some variability between units.

Yeah, I would get them from eBay as John Derby suggested. A couple of years ago I bought a 1.25" to 0.96" adapter on eBay. It came from China in 2 weeks and cost me about 3 pounds including shipping cost... That was a bargain!

Yesterday, I managed a quick observation of Jupiter before the clouds covered the sky. Despite the average seeing, it was clear that the astigmatism was gone. The telescope works as when the cable sling was loosened. Good!

Managed to observe Jupiter and the GRS before the sky became completely clouded. No Io transit though. The seeing was average and windy. Oh well, next time. Wish the best luck to those who manage to observe this event!

Jupiter behind the clouds here...

Good luck with this project, Stu!

Great! Thanks for sharing this!

The screw at the centre attaches the triangle to the underneath platform. The lateral screw prevents the triangle from rotating more than a certain amount, which I haven't measured (5mm -ish?). Vertically, they can move much more (possibly 20mm). Again, I have not measured this.

They support the primary mirror. They look identical to those installed on the triangles of Orion Optics mirror cells.

The adjustable spanner did the job! Very glad that David offered this clue! Anyway, I decided to take off the Glatter's cable sling as it caused too many issues and didn't proved to be necessary. To do so I had to remove the mirror cell from the mirror box, and remove the right angle holders from the mirror edge support. Therefore, I took off the mirror from its cell, partially detached the velcro from the edge holders, and remove the sling from the edge holders. I then removed the cable supports. To do this, I had to detach the mirror cell from the wood base. Finally, the mirror was put back with its cell into the mirror box. Interestingly, collimation was not far off, despite of all this work! After collimating the primary mirror, I checked how this was retained at different altitudes, and there was no difference from before. Good! Very glad that now this issue has been sorted out once for all! Thank you everyone for the support with this. I look forward to a clear night now! Here are a few photos.

I spoke with David this morning. He confirmed that no glue was applied between the right angle holder and the mirror edge support, but that it is possible that some sprayed black matt paint is attaching the two components. He suggested to use an adjustable spanner.

Yes, those right angle clips on the vertical supports are attached with an Allen screw. I unscrewed them in order to take off the right angle clips and found out that these don't come off.. it is as if they have been glued to their vertical support. Maybe the paint went in.

I took the mirror cell out. The mirror clips seem to be glued.. why this?! How does one take the mirror out if the clips are glued? Detaching the edge supports is even more difficult as there is no way to pass a key through that.. 

A nice post by Nils Olof Carlin: "[..] To design a support for the largest mirrors, the sling may be worth the effort - for the next-to-largest, a whiffletree arrangement is fine, but for more moderate sizes, a 2-point support is fine by far, and easily made well. This includes a "normal" 18" mirror and a bit up. If you want an upgrade, practical and economical considerations come into play - Howie G-s sling might be the easiest to add to an existing mirror support." (https://www.cloudynights.com/topic/570249-whats-so-special-about-glatter-slings/#entry7768997)