Baader Steeltrack/Sesto Senso on 200PDS - the missing manual

[discardedastro]

Right, since I couldn't find anyone who'd done this before I did, and because I'd really have liked to have it when I was doing it, here's a write-up with pictures of how a new Baader Diamond Steeltrack NT fits on a Skywatcher 200PDS, replacing the stock focuser.

Spoilers: it doesn't! While all the documentation (including FLO's site) suggests it's designed to retrofit Skywatcher and similar scopes, and the install documentation suggests using existing holes to align the placement of new ones, this turns out to be wrong. The holes are wildly off and so you can't do the alignment using the old focuser holes. Note also the bonus 5th hole on this one - thanks, Skywatcher!

So this got a bit more involved.

I started by removing the secondary, fitting the new focus motor, and removing the screws holding on the old focuser. Here's both side-by-side, ready to go. In retrospect you'll need access to the side "underneath" the focus motor, so best to prep but not fit it at this stage.

Next you remove the four bolts on the Baader plate and slacken (but don't remove) the eight tiny grub screws around the plate to remove the focuser itself. A set of long-handled (not right angled) 1/1.5/2/2.5mm allen keys is a godsend during this, incidentally.

After realising the holes wouldn't align I sat down and did some maths; on my 92.6mm wide hole in the tube I needed a 5.9mm gap above and below to the screw holes. This turned out to not quite be right but I drew those lines in as a reference, using a set square off the front of the telescope and some calipers to measure.

Masking tape on the tube gives a nice surface to mark on and helps reduce swarf when we get to drilling.

I put the base in place and used two small G-clamps through the drawtube hole to temporarily secure it. This let me see I was a bit too far away with my hole placement so I put a centre punch mark about 1.5mm off the lines drawn. On the long axis I just eyeballed the center of the slots in the plate after getting the plate itself roughly centered; I figured this gave me about 5-10mm of travel to fix it precisely, which was plenty. Once all aligned, I stuck some paper in the tube to help catch debris and popped the holes in. I was using a 2mm Bosch HSS-TI bit, followed by a 5mm. I deburred afterwards, just to keep things clean.

I taped over the old holes to provide some light blockage and atmospheric sealing, since my scope lives outdoors.

I had to experiment with the shims - I thought I wouldn't need any, as the instructions note the base is designed for a 8" tube. However I think this actually means 'an 8" tube made by someone who over-sizes their tubes more than Skywatcher do' - I added one shim on each side in the end and that looks snug without distorting the tube.

Note the plate has definite gaps around the tube - if you're concerned about light leakage or dew ingress these gaps need filling, along with the empty screw holes in the plate. I'll probably just put a bit of black foam in the big gaps and tape over the rest.

I then got the plate central to the hole, tightened it all up, and fitted the focuser. This is where the non-right-angle allen key drivers are a godsend - modelfixings.co.uk do a nice range. Note here I've had to remove the Senso Sesto to get at this screw. I used a right-angled allen key to tighten up everything once it was all nipped up.

So that's the focuser actually fitted and the motor fitted in place:

I hacked the end off the power cable for the Senso Sesto because unlike everything good and proper using 2.1mm DC jacks it uses a 2.5mm and I have no 2.5mm to terminal block lying around. I added a couple of blocks to split the camera power supply in two - this definitely needs making neater, but that's another project.

Fitting the Clicklock was easy but fiddly - tiny tiny grub screws galore rather than a screw fit for the adapter. Note the Clicklock requires a minimum length of your 2" component - I had been using a 1.25" adapter which only had 1cm of protrusion into the 2" barrel. This did not work. Fortunately I had another which did.

I stuck a laser in and used a ruler to validate that the focuser was square (measured laser intercept off the front of the scope). Up/down I didn't verify but it looked spot on relative to the spider vanes.

I then sat down for an hour of flipping between collimation guides (Vic Menard's, mostly) and FLO's sight tube/Cheshire to get the secondary back in and collimated. While I've achieved pretty good axial collimation I think my focuser position is a bit too far "down the tube" - this is the first time I've done "proper" secondary collimation! Here's a shot from a Barlowed laser:

And a view down the sight tube - not quite as badly offset as this shows but it's hard to take photos down a Cheshire!

First impressions of the Baader while putting it together are very positive, other than the plate awkwardness it's very well built and feels very solid. Time will tell how well it performs for AP but with the new motor it should be a considerable step up from the stock focuser and the Hitecastro DC focus!

Hopefully this helps someone else trying to make a decision on this focuser or considering how to install it.

[discardedastro]

And just to add some "lessons learned" after a brief first light...

With the Clicklock in place the focus position is very close to the "full in" position, but there's still plenty of room (it sits around 5000-7000 in absolute terms). The standard low-profile mount might be all you can get if you're already fairly well racked in at focus on the stock SW focuser - I was usually about half-way out or thereabouts.

It works perfectly, as far as I can tell, in any case - mount issues stopped me getting a perfect in-focus frame but the V was clearly defined in Ekos autofocus. Racking out to either extreme and coming back to focus was absolutely dead on. I'm running the motor in the "Medium" preset, which seems to work fine.

[Fedele]

Hi, well done

for all

i want to buy a Baader BDS SC for my Mewlon and i want to motorize it. 

1)  Sesto Senso 2  must be connected to  the micrometric wheel of the Baadser right? so you lose manual micrometric control of this

2) What happens to focus both by hand and with the sixth sense at the same time? is it necessary to "release" the control with the sixth sense which thus loses data and position?

3) The options for a manual controller of the Sesto Senso 2? onlu via  virtual pad=?

4) is the ZWO EAF  a best option? becase probably it attaches to the coarse knob on the left side of the baader leaving the macro and micro knobs on the left side free. plus it has an optional hand controller

 

thanks

Edited March 6, 2021 by Fedele