Paul has come up with this ingenious solution to the problem of a cricked neck when looking through the polarscope on these popular Sky Watcher mounts.
The photos below show how the 90 degree viewer and fitting are assembled, noting the nut used to clamp it together.
Paul has very kindly made one of these for me using a second hand Nikon DR3 right angle camera attachment off ebay (approx. £6). He has made the hole in the plastic fitting a tight fit on the short thread of the DR3 such that no nut is needed. He has learnt how to carefully enlage the bore of the plastic fitting so it is a snug fit in the polarscope eyepiece…a bit tedious because it’s trial and error and must be done very carefully to ensure that the bore is not accidently made too large. Patience needed and lots of cups ot tea! The finished product is a tight fit and needs screwing onto the thread of the viewer. It should be a snug push fit onto the polarscope eyepiece. Paul used a 32mm Waste Compression End Plug costing £1.50 from “Discount DIY Store”, Swadlincote High Street, Swadlincote, Derbyshire, UK.
In use: Fit collar to viewer first, then push it onto polarscope eyepiece as far as possible – see photo. Try different angular positions if its too tight to go on. The collar should go over the eyepiece and over the polarscope tube as well.
To focus polarscope, Paul has found that he needs to unscrew eyepiece about 5mm so he fitted an 0-ring onto the thread for eyepiece to clamp against and keep eyepiece tight in the focused position.
Prime focus with Canon 60D attached to SW200p last night when Saturn was at culmination (15 degrees) but still low enough to give a blurry image. My first photo of this planet. Jupiter was even lower but with iso800 the 4 Galilaen moons show up well but planet massively overexposed. The nearby full Moon also reduced the contrast. Attempted eyepiece projection but gave up trying to get the fast moving image in the camera lcd. Have an HEQ5 Pro for collection from RVO on Monday which should help track images and eventually get photos of some faint DSO’s. Thanks to Andy T for the demo of his HEQ5.
Having owned this mount and scope for nearly a year, I am thinking of adding a GoTo/tracking function by purchasing the SynScan Pro V3 Upgrade kit but would first like to seek the views of any members who have already added this feature or been down this route. At around £300 it should be an excellent accessory and all the utube videos and internet reviews support this. Alternatively, is it possible to add just motor drives (at around £100) and control these with planetarium software, like Stellarium or Skysafari?
Any views, in favour or against are very welcome. Thanks.
After hearing about the rapid set up and simplicity of a Dobsonian mount for casual observing, I thought I would investigate how to get one as an alternative to my EQ5. Strange that these mounts cannot be bought separately, except at Orion Optics UK, where I was quoted a high price. This set me on the DIY route.
I decided that I wanted the capability to adjust the tube axially (for balancing) and rotationally (for comfotable viewing position), as with the EQ5.I also wanted easy transfer of the tube between Dob and EQ5 (no tools needed). After a week of research, I settled for a hybrid that included a features from this article: http://www.scopemaking.net/dobson/dobson.htm, The Sky at Night articles in Dec 2014 and Jan 2015 and the Orion Optics design. Originally, I was going to design the rings and dovetail bar to be interchangeable, but when a set became available I settled on a separate ring set for each mount.
I won’t go into detail about the build/assembly but show various stages in pictures. The main stages are; 1.mods to the ring set, 2.cutting, shaping and painting, 3.bearings and the 4.optional brake. Anyone who wants more detail please contact me.
1. Modify ring/rails assembly.
Trunions: PVC 160mm pipe plugs (Buildbase, Newhall, Swadlincote). Protect bearing surface with masking tape. Locate centre and fix to bar with 1/4″UNC fasteners (Pugh & Sanders Ltd Burton on Trent).
Shape and fit 2nd ‘rail’ from 10mm plywood. Fix to rings with 1/4″ csk head screws. Locate trunion on centreline in same position exactly as other trunion.
Trial fit completed ring/rail assembly to scope
2.Cutting, shaping and painting frame
I used 18mm mdf for the base and sides and 10mm plywood for the front, back, rail and accessory tray. Use plastic fixing blocks and screws to hold everything together. No adhesive needed. Take basic dimensions from the article referenced above, except width of front and back, noting that alt bearing box is not needed and friction brake needs to be included.
Mark out parts using trammel to draw circular base.
Cut with jigsaw and smooth with rasp and glasspaper
To obtain width of front and back, measure distance between trunion flanges and add 10mm.
Use plastic fixing blocks to assemble, drill through upper base and screw to frame, bolt to lower base, trial-fit scope assembly. If all goes pear shaped, use as a ‘lazy-susan’ coffee table!
Trial fit 3 feet 120° apart.
Use jigsaw and ripsaw to cut holes to reduce weight and improve appearance.
Hang from washing line for painting – 2 coats minimum. Have a coffee between coats!
For altitude bearing use two 2mm thick ptfe sheets, drilled and countersunk in centre for small csk head screw.
For azimuth bearing use 3 Magic Glides (Wickes) spaced 120° apart within 300mm circle .
Use M10x60mm carriage or ordinary bolt and M10 Tee Nut (Amazon or ebay) inserted upside down for pivot in lower base. Tighten so it will not fall out or turn when M10 Nyloc nut is tightened.
For upper bearing use 12″ vinyl record (grooves make for low friction). To form a good bearing for the bolt in the upper base use a brass10-15mm reducer plumbing fitting (Wickes) drilled out to 10mm. Secure bases with oversize washer, spring washer and M10 Nyloc nut. Tighten only enough to take up slack.
Small spacers are needed to prevent sideways movement of scope assembly. Spacers are squares of ptfe fastened with small screw and spring washer fitted between side and flange of trunion. Trial fit to to gauge the spacer size and position of spacers.
4, Friction Brake Feature – Optional
This feature prevents the scope moving if the assembly becomes out of balance, although there is the option to slide the tube axially.
Attach another strip of ptfe to top of curved section of brake. Attach small hinges between brake and side using small 90° brackets to allow screwing into face of wood – mdf will split if screwed into edge! Attach a ‘Brighton sash window catch’ (satin chrome finish from Screwfix) such that it can be released to allow the scope to be lowered into place and tightened to stop movement or lock the scope. Fit accessory tray to front and hooks to sides for clipboard, glasses etc. Extension legs can be used if elevation is low or if the ground is long wet grass. To make carrying more comfortable, fit a length of 12mm soft clear plastic hose cut lengthways to upper curve of the front.
I had great fun making this but have used it only briefly to observe the Moon and was pleased the way it moved…but I still like the fine control provided by my EQ5 control cables. Now how can I add this feature to the Dob…?
After some discussion with Andy T on the benefits of a laser pointer for finding objects, I decided to get one of these. The laser and the bracket are yet to arrive but the extra shoe needed to mount it to the tube, ordered from Harrison Telescopes, arrived in 3 days. This is now fitted with the M4 countersunk screws and black nuts supplied. I will outline the method I used and tools needed, for comparison with Andy’s adhesive-based method (10 March) so you can decide which to use.
1. Make sure you think hard before you decide on the location; drilled holes are permanent. I placed mine about 20mm from the finder-scope shoe, to match the gap between it and the focuser base.
2. Attach masking tape to the area where it is to be attached.
3. Rest the tube horizontal up against a firm support with the focuser aperture above the area to be drilled, to prevent swarf/cuttings getting in. Also, I put newspaper directly under the drilling area to catch any cuttings and masking tape along the inner edge of the stiffener on the end of the tube. Time taken in preparation is well worth it. See the photo below. I would not advise doing this task with the tube in the mount.
4. Mark lines on the masking tape and use the shoe as a template to mark the locations of the two holes.
5. Check that the holes will clear the reinforcing plate (if fitted) inside the tube used for the finder-scope shoe.
6. Tubes are made of thin steel, work-hardened by the rolling process, so sharp drills are essential. Start with a small size drill, say 2.5mm and work up, in steps of 0.5mm, to 4mm diameter. This minimises the force needed to break through initially and subsequently to increase the hole size. Small drills break easily so do not apply too much force, have only a short length of drill protruding from the chuck and try to align the drill radially to the tube.To make sure the drill chuck could not touch and mark the tube, I pushed a rubber tap washer onto the drill, masking tape alone is not thick enough. Make sure you are in a comfortable position and able to control the pressure applied by the drill.
7. After drilling one hole, loosely attach the shoe and check the marked location of the 2nd hole.
8. If the 2nd screw will not insert, increase the hole size of one hole, or both if needed, to 4.5mm. Mine were fine with 4mm diameter.
9. Remove masking tape and the paper inside the tube and attach the shoe. I used a small spanner (shown in photo) to hold the nuts while tightening. Take care not to shear the screws as they have a small cross-section and not to scratch the black paint inside the tube.
Once the bracket and laser arrive I will post a photo of the finished assembly, soon I hope!
Have now fitted bracket and laser but not used it yet. It was quite a loose fit into the shoe dovetail (left in view below) so needed a small aluminium shim. The SW finder bracket is not a brilliant fit either but at least it tightens up before the clamp screw runs out of thread. I think it looks the part at least (see below).
Total outlay for all 3 parts was about £25, all bought separately off ebay.
I have been asked to share some of my astro photos taken over the last 18 months, some with just my tripod mounted Canon 60D with a 200mm telephoto lens and some with this camera at primary focus on my EQ5 mounted SW 200P.
This was taken a few days after the clouded-out lunar eclipse of 21 January. I was a bit disappointed about the eclipse but I got a good shot in the end! Its a general wide angle view of the garden stacked (using simple star-trail stacking software) over 7 zoomed-in shots, taken 2.5 minutes apart, of a waning setting moon.
This is about 3 hours worth (!) of 30s exposures giving an apparent rotation of 45 degrees. This was one of my GCSE projects to evaluate the length of Earth’s sidereal day by extrapolating the measured angle of rotation and exposure time. I am still amazed at how well these shots reveal the star’s colour. I used PhotoImpression to get a negative of the image, printed it at A3 and drew construction lines from which to measure the angle of rotation. I did this with 3 separate dates to get an accurate figure. A lot of work!
The photo below is a 30s exposure of an aircraft flying left to right in front of Orion while banking away to reveal its wing lights. Taken just after a star trail session, so timing was pure luck but I have since noticed these planes always follow the same path from East Midland Airport.
Talking of Orion, this is its nebula taken through the SW 200P with a single shot of 1s exposure. The telescope’s fast F5 rating registers the faint nebulosity with quite short exposure times so the short star trails do not mess up the detail too much. Just needed some slight colour enhancement from MS Picture Manager. I must try this again with some manual tracking until I get motorised drives for the mount.
If you only have one telescope, the Skywatcher 200P, with adaptors for attaching a DSLR, has got to be high on the list.
These were taken this morning after my weekly visit for running the Rosliston Parkrun. Proud to say I am a RAG member and all involved in this long-term project should be proud of what they have achieved.