One for ZS71 owners

[Demonperformer]

Right, I've been having a closer look at my setup:
The distance from the end of the focusser to the outer edge of the compression ring is 5mm, and the distance to the inner edge of the ring is 12mm.
Measuring from the scope-side edge of the large chunky bit of the FF/FR with the writing on it, the distance to the (ever so slightly) narrower bit is 2-&-a-bit mm, and the distance to the end of that bit is 16-&-a-bit mm.
If I leave 10.5mm of the FF/FR from the large chunky bit outside the scope OTA, this means that the narrower bit (into which the compression ring is presumably supposed to fit) is from ~8mm outside the OTA to ~6mm inside the OTA, i.e. barely reaching the compression ring (which is 5-12mm from the end of the focusser) at all (only just over 1mm overlap).
To get the compression ring to fit fully inside this narrower bit of the FF/FR, the furthest "out" of the OTA it could be is 16+mm (the distance of the furthest edge of this bit) minus 12mm (the distance of the furthest edge of the compression ring), which is 4+mm, not 10+mm . My bwain 'urts!
The images (hopefully) make clear what I am trying to say [and also show that there is only one screw, not three].
But based on my contributions to this thread so far, whether what I am trying to say bears any resemblance to what I am supposed to be doing is a far more problematical question!
Thanks.

[Demonperformer]

7 hours ago, carastro said:

I have no recollection of a compression ring, but maybe I never noticed

It is far from obvious that that is what it is until someone points out that it is "just a strip of brass" sitting inside the focusser tube.

I had actually noticed there was a different-coloured bit inside the focusser before, but had thought that was a weird place to decorate the tube, without realising that it was (i) not a part of the tube but an additional bit slotted in, (ii) rotatable [with a bit of ingenuity], and (iii) the screw was at the same distance from the end of the focusser as it.

[Demonperformer]

Just been looking again at your picture of the "2015 Zenithstar" ... something has been bothering me and I have finally worked out what it is.

In the picture, there is the main tube, then a big chunky ring (that stops the tube disappearing into the scope completely) and then there is another less-chunky ring (which looks as if that is where the compression ring sits).

On mine, there is no second less-chunky ring and the compression ring sits in the (one and only) big chunky ring.

No wonder I haven't been able to relate pictures of the ZS71 to what I have!

[Alien 13]

The scope comes with a 1.25 inch eyepiece adapter that slots into the main focusser assembly, this too has its own compression ring but only one thumbscrew. The main 2 inch part should have two thumbscrews and a third hex screw underneath to equalize the pressure applied to the FR/FF.

The way I fit mine is to insert the FF and adjust the screws until it just grips you should then be able to slide the FF between the two undercuts in the barrel of the FF so you know its in the "safe position", final adjustment is the to pull the FF out slightly so it hits the undercut end stop then tighten everything up. This ensures that when the scope is pointing up the FF cant slide if the screws have loosened slightly due to expansion/contraction in the cold weather.

Alan

[Demonperformer]

Right, so that explains the additional chunky ring. Mine didn't come with that 1¼” adapter.

As you can see from my above photo, the focusser has only one screw - presumably an older version, as per Oddsocks' earlier comment.

[Oddsocks]

3 hours ago, Demonperformer said:

To get the compression ring to fit fully inside this narrower bit of the FF/FR, the furthest "out" of the OTA it could be is 16+mm (the distance of the furthest edge of this bit) minus 12mm (the distance of the furthest edge of the compression ring), which is 4+mm, not 10+mm

 

2 hours ago, Demonperformer said:

As you can see from my above photo, the focusser has only one screw - presumably an older version

Yes, from your posted image and your calculations it seems you have an older version of the focuser which has not been designed well for use with the Flat 6 (out of interest is your focuser a rack and pinnion or a Crayford?).

Using the W.O. stated "safe distance" will leave your flatener and camera not secured by the safety undercut on the body of the flatener and is not "safe" at all, it could easliy fall out as the temperature changes during an imaging session and the various bits expand and contract.

Given that, I will retract the advice I gave above of not screwing the flatener into the draw tube baffle threads and suggest this is the only way you ensure a solid safe connection - BUT - if you do so it is a risk that the flatener will jam, damage the threads or the matt black anti-reflection paint can be scraped off the baffling in flakes.

From your calculations it seems you will need to screw the flatener into the draw tube and leave a gap of no more than 4mm between shoulder of the flatener and end of the draw tube so that the compression ring sits fully in the safety undercut.

As an engineer it would be easy to make a judgement of whether this is a good idea if I had the scope and flatener in my hand, making a diagnosis "remotely" is not really a good idea, it is not after all my equipment to risk damaging if I am wrong!

At this stage I would say an email to William Yang at W.O. with your findings and photos, including the serial number of the focuser and scope might be a good idea, asking if he recommends screwing the flatener into the baffle threads, or if the Flat 6 is compatible with your model focuser at all.

 

[Oddsocks]

This thread seems to be covering much the same ground:

I was going to say earlier, while it might seem a major undertaking, if this was my scope, and you don't hear back a sensible answer or solution from William Yang at W.O. then I would try a quick evaluation set-up as-is, check for good coma correction across the field, ignore any slight tilt that may be caused because the flat 6 is not setting square in the draw tube and if all is good then, assuming the scope is going to be a keeper for you, I would take the focuser off the scope take the draw tube to a local engineering shop and ask them to mill or lathe-turn away the inside baffle threads to extend the clear part of the draw tube by 12mm, allowing you to fully insert the flattener into the draw tube, then repaint the exposed shiny aluminium with Humbrol matt black enamel No.33 plus a coat of "blackboard paint" over the top if necessary.

The cost of the lathe turning or milling should not be more than thirty quid and the paint around a fiver.

You would just need to be sure that the focuser will be able to extend the extra 12mm to still bring the image to focus otherwise this would be a non-starter and require a bigger modification to the focuser-tube coupling.

I expect you have had enough of my input by now so I will just watch the thread and see how you  solve this in the end.

[hiroshiman]

I am waiting for my reducer so I can't tell you how mine reacts yet. I do have the compression ring with 3 screws and the 11/4 reducer with a compression ring. Do you have a rotating focuser bloc on yours ? Mine has no protuding screw for that, but there is one according to the manual.

I am starting another thread for some issues/questions as well.

Cheers

[Demonperformer]

Yes, the focussing block rotates. Just to confirm, the screw, if you have one, is the one arrowed in this picture.

[Demonperformer]

Just seen your other thread ... clearly that is the screw that is missing.

[Demonperformer]

Having discovered that, as well as the one thumbscrew I have, there are also two grubscrews operating on the compression ring, I am thinking it would be a good idea to replace them with thumbscrews to give maximum control.

Does anyone know exactly what size the thread is on these (e.g. M number?), so that I can get thumbscrews that will fit?

Thanks.

[hiroshiman]

Hi mate,

It took ages (ages is about 5 weeks) for the products I had ordered from WO to arrive. I didn't have time nor good weather to try it, but I can tell you that the Flat6A goes all the way inside my ZS71. Hope in the meantime you figured out a way to be satisfied with your setup.

Cheers