Hi to fellow Amature Astronomers, I have a 10 inch Schmit Newtonian with a standard rack and pinion focuser, coupled to a Skywatcher electric focuser. The standard rack & pinion + the Skywatcher e/f is reasonably good,however it has a certain amount of lash for prescise focus. So i would like to fit a device with a finer control, but that means removal of the corrector plate. I would be gratefull for any advice
From what I know of any of the Schmidt corrector family, they are all matched to their optimal image position. If the plate does need to be removed, and the primary too for this focuser replacement, you will need to very carefully mark the position of the corrector plate and the primary in their current placement BEFORE removing anything. Otherwise the corrector/mirror arrangement won't be at its best.
Focuser wise, there are many good options. What you will need to be mindful of is that what ever focuser you select does have the travel and relative placement of the mechanism to the optical cone path. If too low in profile, you might need an extension tube to achieve focus. If too proud, you might not achieve focus with those EPs needing a lot of in-travel of the draw tube.
Just some things to keep in mind. Others will expand on precautions/requirements, and have focuser suggestions.
Removing the corrector plate on an SN10 is very straightforward.First ensure you have somewhere to support the corrector plus secondary , i have done this using a container that supports the outside of the corrector cell with sufficient depth to accomodate the secondary mirror .Then place a length of white electrical tape on the ota close to the inside edge of the corrector cell , place a second length of tape alongside the first on the inside edge of the corrector cell. Make fine pen marks across the two tapes in several places to enable accurate placement of the cell on reassembly. Now undo the 4 screws holding the corrector and carefully pull it out and place it on the container. As far as replacing the focusser im sure someone else can advise you.
regards philip
Perhaps you can replace the rack and pinion with a GSO Crayford, maybe even find a used one. If so, it's quite easy to make up a simple one-piece aluminium bracket to mount your Skywatcher focuser to it. I did this with my SW 8" newt, and it works just fine. No backlash.
If you later buy the Shoestring FCUSB, it will also drive the SW focuser, and allow you to remotely focus via a PC USB port if you wish.
Thanks Mike, the craford focuser is the go. Didnt quite no what a shoestring was untill i looked it up, lol, its definitely the way to go. Yours in clear skys.girko
I have the 8 Inch meade S/N and have the same problem. Changing to a crayford (which i have to do shortly) is the way to go but just be mindful of the fast focal speed of the S/N scope.
There is a crayford on the market make by Moonlight which you can purchase the adapter kit (with extension tube) for the S/N, these are available through theastro shop in Queensland ? astroshop although they apparently can be imported from the USA where they are made . This is important so that you don't have to redrill mounting holes and chew out a larger hole in the OTA.
As I do both imaging and viewing you are continually removing and replacing the extension tube anyhow. Mine is also complicated as i also use binoviewers that require a barlow nosepiece to get to focus.
Thanks for your friendly advice Alexander, i will save that to file in the old grey matter.
its definitely the way to go. Yours in clear skys.girko
