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Looking at the tracks/wheels from Brundle's I'm trying to decide on which wheel size to choose. I'm thinking the 200Kg per wheel is way OTT but that's the loading option I'm looking at with a 20mm round top galvanised track. The wheel options are either 60 or 80mm diameter. https://www.fhbrundle.co.uk/groups/13SWR200__200_kgs_Weighthttps://www.fhbrundle.co.uk/groups/13SWR200__200_kgs_Weight Any thoughts welcome

Thanks Steve - not what I wanted to hear re CEM60's but...

Looks superb but on dew laden nights isn't the carpet going to act like a sponge which will need a dehumidifier running during the day to remove the water - especially when a wet day follows a damp night...?

No James - it got dismantled because people viewing the house were put off by it. The observatory was built in sections apart from the roof and it ended up being a posh chicken run for a guy in the village...

My earlier obsy while in Devon

Pondering whether to carry the cladding right across each elevation, mitre the corners and hide the corner posts...?

Understand your thinking - tracks would never clog with leaves and ice etc. But not as practical with a roll-off roof as it would require many more wheel pairs the entire length to the observatory and run-off beams. The actual track would be shorter but for me that would be the only benefit.

My intention is to use plywood plates across each corner.

The intention is to park the scope in a horizontal position, certainly the refractor. The Edge HD8 won't be a problem but I'd rather just have one park position regardless of which scope is on the mount. I like Olly's dual tec mounting but the only scope I have I would duplicate is the AA Wave Series 115... (dreaming again...)

Update In the original drg's I never allowed for scope clearance when the roof rolled back. Doing this has meant moving the door to the opposite end (made it bigger too) and leave more of the end wall in place around the door. I'm sure there will be other changes along the way... TBC

Hi James - Yes. I was in North Devon near South Molton but have moved to Hereford now. Your build is one that I've pinched a few ideas from. I thought 4 per side because I intended using rubber wheels to keep the noise down when opening/closing the obs. The obs will be built parallel to and quite close to a neighbours house/fence along the north side. I won't have any view of the north sky so PA will be by other means although once set it should be a periodic check/adjustments. I put the wrong image up first - there is a door between the track extensions... EDPM is at the top of my list at the moment but would like something that doesn't heat the obsy up. My last one had a reflective ali sheet with Cellotex insulation stuck to its underside - killed condensation. Francis

I've been thinking about another obsy ever since we moved and I had to dispose of the last one. So I've been sketching out ideas, pinching ideas, looking at materials and finally come up with what I feel I can a) actually build, b) functional c) have permission form the boss to! So I've attached my initial drawings. The obsy building will sit on sleepers (having had to dig up the last lot of concrete foundations it's not something I want to do again). Tri-pier / CEM60 with sit on a concrete pad under a suspended wooden floor Walls are shiplap on 3x2 frames each of which is secured to a 4x4 corner post. OSB linings with insulation behind Roof will be in marine plywood (with a covering to be decided on) and will run in a 'U' shaped track with 4 wheels per side. The track will be longer than the building width to give me a little more sky to the east.

First image is without the field flattener with Nikon DX format sensor (APS-C) Next is the DX sensor with flattener, final 3 are with flattener and FX Full frame sensor. All exposures are around 60 sec, there is some trailing due to imbalance especially with the FX 800E body.

Update - the 73A flattener arrived today and as it was cloudy, raining, cold I thought I'd adjust the flattener to WO's specs (11.4 on the barrel scale), put a full frame DSLR (Nikon 800E) focus on an effectively infinite chimney, point said scope at the cloud base and take a look at the results. There are two images attached. One is as-is camera set to auto. The second is the same frame but given a mild stretch in Lightroom. Mottling in the frame area is I think from variations in the 'greys' of the cloud base. What I was really interested in was the corner vignettes. I'm pleased as that amount of 'corner' would likely be lost in stacking alignments or taken out with flats.

A few photos to show my concerns over the balance point: Images 1 - 4 show the balance point as it was last night - very near the end of the dovetail bar. Image 4 shows the locking screw's position blocking further movement of the dovetail bar. Image 5 shows the dovetail bar shifted back after removing the locking screw.

Miraculously it cleared late evening here, not brilliant but good enough to give the scope a quick test. I now know that I will need to be more careful with balance and to that end I will need another small weight on the counterweight bar and also shift the dovetail bar further under the focuser as I didn't feel the dovetail bar was fully supported across the Sky Adventurer's Dec plate. The built in Bahtinov mask worked brilliantly making focusing a simple task. There was some trailing to images but the fall-off in image quality from centre to edge of my DX (APS-C) size sensor is quite marked. The trailing I'm putting down to the balance issues and the dovetail bar position making the mounts axles non orthogonal. Smaller sensors using the centre of the fov will be fine. I've added an overlay to one of last nights images showing the sensor sizes I have. For me as this was bought for imaging - it looks like I'm going to have to get the dedicated field flattener at some stage. Whilst not unexpected I was expecting better. On a more positive note before packing everything away last night I put a star diagonal (2 inch) and my ES 68° and 82° eyepieces on the scope and had a quick look around. As with looking at the tree yesterday when unpacking the scope, stars were crisp with good contrast, focusing was very precise - a nice ending to a new scopes first day. So next I'll move the dovetail bar further back (focus lock screw will have to go to do this), make a small additional weight for the Star Adventurer to better control the overall balance... Image is 5x90 sec 1600 iso aligned and integrated in PI with a histogram stretch. TBC

This scope arrived this afternoon so this is a first impression of the scope. William Optics ZenithStar 73mm APO – Purchased from First Light Optics, Exeter, UK. March 2019. Why a William Optics 73mm ZenithStar APO There are loads of this sized telescope around, rebadged, trinkets added, paint jobs. So Why a WO ZS 73 APO ? Originally, I started looking at the WO ZS 61 APO to go on my Sky Watcher, Sky Adventurer Pro pack mount. I’d been using the mount with various camera lenses coupled to either of my Nikon cameras (D5100 or D800E). I especially liked the image fov's from lenses in the 400 – 600mm focal lengths. The mount handled them well and unguided subs of 100 – 300 seconds using an intervalometer show very little signs of star trails even with the occasional 600 second sub (due to faulty cable connection). The WO ZS 61 APO’s focal length at 360mm was just that bit shorter than my 400 -600 ideal range so here enter a WO ZS 73 APO. With a 430mm focal length it crept into my ideal range. At f5.9 it was fast enough (photographically), it came with a variety of goodies and it was not too heavy for the rated loading of the Star Adventurer (less than one of my camera lenses). I looked at longer focal lengths too but their weight didn’t suit the mount when camera, finder etc were all taken into account. So, I placed my order with FLO and it arrived very promptly (along with the clouds). It arrived double boxed with semi ridged black foam inserts protecting the contents extremely well. In the box and assembly: The WO ZS 73 APO OTA with two finder scope rings (attached – but removable) A vixen profile dovetail bar anodised gold (matching the finder rings and the scope’s trim) A 2 inch to 1¼ inch reducer. End caps, the front-end cap hides a clear Bahtinov mask feature. The 2018 version has a thermometer fitted in the end of a 1:1 focuser knob. The focuser has a helical rack-n-pinion adjustable with 1:1 and 10:1 motion control’s Putting it together meant nothing more than adding the finder scope adjustment screws to the finder scope rings, respacing the OTA rings along the dovetail (if required) – job done. Visual impressions: The body has that clean medical exactness about appearance. It’s there to do a job and it intends to do it. The coloured trim adds colour in a not too subtle way. Overall clean, minimalistic and functional. Other impressions: I’ll start with the vixen style dovetail bar. What I like about it is the asymmetric hole layout along it’s length, allowing it to be switched 180° to better achieve a balance point* and still retain adjustment on the tube ring positions. It’s 2 inch helical rack and pinion focuser is smooth in operation and I can feel no play even when extended fully with an APS-C DSLR mounted. Focus knobs are large enough for gloved hands when used on colder nights. *The focus lock screw on the underside of the focuser to me is poorly positioned as it hinders the positioning of the dovetail bar if you put a heavy camera or eyepiece assembly in the focuser. The dovetail bar can’t extend backwards far enough for balance unless this screw is removed. There are three knurled screws holding accessories in the focuser, these press onto a compression ring to secure diagonals, extension tubes etc. I’ve put a 2 inch diagonal and 24mm ES 68° eyepiece in and looked at a tree coming into leaf and I have to say very impressed with the contrast and detail. I was a little disappointed to find that to put my DSLR on I needed a 35mm extension tube to get the scope to focus. Considering how prominent astro imaging is spoken about in the blurb a suitable extension tube should I feel have been included. Looking down the interior of the OTA from the focuser there are numerous baffle rings along the focuser’ draw tube. Tube rings have comfortably sized knobs with nylon washers which either secure or release the tube easily. It’s lens shade/hood slides easily but with enough resistance to prevent it sliding back if viewing near the zenith. There is a small knurled screw supplied to fit into the lens hood but on mine there’s swarf or a bad thread form and my screw doesn’t tighten and secure the hood. The supplied finder rings are very sturdy and will do the job of securing and adjusting the finder scope well. What I can’t understand is the size and proportion of the adjustment screws for the finder scope. They’re way over sized – especially if you look at the size of knurled screws used to secure equipment in the focuser. Looking forward to using this in anger under the stars Once I have some results to share I’ll post them to this review. Francis

Remember you do not need to level an EQ mount before doing a PA. If you're having problems with bolt adjustment then raise or lower one of the tripod legs to compensate and keep the bolt within a useable section of the thread. I had to with my NEQ6 Pro.

I did spend quite some time after getting the SA aligning the reticule on as distant an object as I could. Took quite a lot of very small adjustments before I was happy that rotating the mount whilst looking through the polar scope showed absolute minimal movement of the central cross hair. If your using a phone app to locate where Polaris should be placed make sure you have the correct settings in the app. Mine has a visual setting and a telescope setting - one being 180° from the other.

Yes, just the polar scope. Used a phone app to locate where Polaris should be and set the mount accordingly.

Hi Graham, The subs were circa 100s, that's determined by the mount's firmware. I'm using the original firmware which when I connect the camera to the 'snap' socket on the mount gives - fits header says 99.4s. Note: the bloating round the stars is caused by primarily two things: the condition of the lens and the full spectrum mod on the camera making it more sensitive to IR/UV which doesn't focus to the same point as the visual spectrum.