Moonlight has finally started offering the adjustable adaptor for the MN190 scope. Previous fixed versions of the install adaptor did not have any provision for adjusting the focuser centering over the secondary, leading to problems in trying to make a focuser upgrade work (as the Moonlight would be slightly off centre and people would try to move the secondary to centre it under the focuser, with bad consequences). The new adaptor, based on drawings I made for Ron, replicate the adjustability of the stock focuser.
Anyone ordering a replacement focuser for a MN190 from Moonlight should specify the Newtonian, 2" travel comp ring option, (and the dual rate knobs and shaft lock are a good idea for imaging). You will need to pick the MN190 adaptor from the list under the Install Adaptor page for the Newtonians, it is not shown on the focuser pick page.
That is correct, the white one was the Orion version, some of which had single speed focusers and larger secondaries (63mm). The black Skywatch version was generation two and had a smaller secondary 26% (50mm), just big enough to fully illuminate an APS-C sensor, and a dual speed focuser with the unique internal slide out focuser extension tube.i believe the new Orions now share the same focuser as the Skywatcher but not sure about the secondary size but a search says the Orion is still 63mm. I have imaged with my Canon which has a APS-C sensor and had no field illumination problems with the 50mm and obviously it is a bit more contrasty with less central obstruction.
My Moonlight focuser and adaptor for the Skywatcher MN190 arrived today. I will be installing the Moonlight shortly. Attached are a photo of the stock focuser with it's slide out extension tube, and the new Moonlight with the adjustable (slide) adaptor - which give you the ability to precisely align the focuser tube centre with the secondary mirror centre spot. There is no need to remove the corrector plate for this installation as the focuser nuts are captive on the inside of the tube (so I believe). More soon.
It did not take very long. Removed the old focuser, just remove the four screws holding it to the tube (keep the screws and washers as you will need them to mount the Moonlight). The adaptor matches the tube curve so it sits down on the tube nicely. Checked the line up of the adaptor holes with the tube holes and they matched as they should. Put the four original screws and washers back onto the tube holes and checked clearances and ability to slide the adaptor for secondary alignment, all good. One annoying little thing was the original screw washers were a fraction too small, and as we know with washers sometimes they are not all the same size. I had one washer that slipped down into the gap. So off to Bunnings where I picked up some M3 (the screws are M4 by the way) stainless washers to go under the stock washers. Why M3 washers, the hole was just big enough for the M4 screws and the diametre was about 0.8mm greater than the stock washer - just enough to grab the adaptor recess lip and not bind during sliding. Your stock washers might not need to be changes, I left the old ones on top to hide the S/S washers underneath. I tried the two adaptor spacers included in the kit (1/2" and 1"). Measuring against the stock focuser travel, I decided to use the 1" spacer as it stopped the draw tube from going down into the light path in the tube. With the focuser in place on the tube I used a Cheshire tube to line up the centre of the focuser with the secondary spot, then tightened everything up.
Cleaning the Corrector (Optional).
I decided to go ahead and clean the corrector and secondary mirror as long as I had it on the table, as they had not been touched since I bought the scope a couple of years ago, and I wanted to vacuum out the tube. Removing the corrector is easy, just loosen off the black plastic retaining ring on the front, don't lose the screws. Do not try to remove the white steel front ring, it is not necessary. Place a small piece of masking tape in the shape of an arrowhead on the ring and a small sharpie mark on the edge of the corrector as alignment marks for later. Then find the three edge adjusting recessed screws on the side of the white front ring, and loosen these just slightly all the same amount (these screws lock the corrector in place and centre it in the tube).
Once that is done the corrector should be able to be pulled out of the ring by the secondary hub (take the screw on cover off so you can grab it). Careful! Lay the corrector on a soft clean t-shirt or towel. You can clean it with distilled water and cotton swabs like most mirror cleaning tutorials describe, secondary as well. I use a puffer to blow the water droplets off the glass. When dry reassemble in the reverse order as outlined above. Do not touch the surface of the corrector when your putting it back in the ring, hold the edges. Once you have the corrector back in place, and before you lock it down, make sure that the secondary is properly aligned to the focuser, if you placed a witness marker on the ring and the edge of the mirror it should be perfect; I checked it through the Cheshire tube to make sure the secondary was centered and the mirror not rotated.. Replace the black ring, and tighten the three edge lock screws a little at a time in the same amount to lock it in place. You can now clean the exterior of the corrector if you wish in the same way as described, although I prefer to use Bintel UHTC cleaning fluid as it takes off any gum tree sap micro droplets that might have settled on the outside.
Last step was a full collimation check and adjustment.
Star test will happen when I can get some clear weather.
Photos attached.
Very nice Glen
What do you use to clean the corrector with? Lint free tissue?
On the inside surface and secondary just distilled water dabbed on with a cotton ball, ala mirror cleaning technique. I let the drops run off and then blow any others off the surface using my hand puffer, and dry with lense tissues if needed.
On the outside surface I use Bintel cleaning fluid dabbed on the surface, to prevent gradient evaporation deposits I do wipe it clean with lense tissues.
I am imaging with the MN190 and the stock focuser has an unique internal 2" extension tube which slides out of the focuser, the locking arrangement of the extension was a single screw and there was some slop in the extension system. The stock focuser while adequate stuggled with a combined filter wheel and camera setup, it also lacked a locking system other than cranking up the tension adjustment. The stock focuser is fine for visual use and light imaging gear.
Completed my first imaging run with the new focuser last night and it worked perfectly as we expect from Moonlight. As with any new configuration it took a bit of time to work out the exact focal point position for my camera but once locked in position it was stable all night long. There are a couple more photos attached. Note that my choice of spacer means that I run with the tube extended more than if I had added the smaller base spacer as well; this was my choice because I wanted to keep as much weight off the focuser as possible. The focuser tube in that position does not leak light as far as I can tell, and it is rock solid with no slop in it. This position also allows me to get to the lock screws easily.