Upgrade of Unitron Focusser.

kevy02 (Kevin) · #1 27-05-2012, 03:03 PM

Hi all, I would like to replace the existing focusser on my 4" Unitron with a 2" Crayford type to accept the larger eyepieces.Now, I might be missing something,but the existing focusser is held in to the OTA by a number of screws, but the screws have nuts on the inside.How do you hold the nuts on the inside in order to withdraw the screws. Cheers. Kevin.

alocky (Andrew lockwood) · #2 27-05-2012, 03:33 PM

Depends what Crayford you have in mind. You will find there is actually a threaded end cap that the Unitron focuser is screwed into. Feathertouch actually make an adapter that will go into this thread.
I bought a JMI event horizon for an SCT and got a local machinist to make an adapter. If you're interested, I'll put up some pics.
As to your original question, I use a blob of grease to hold a non-captive nut in place. Once the screw nips up it shoukdn't move, but if you unscrew the focuser first you will be able to get in there with needlenose pliers.
cheers,
Andrew

kevy02 (Kevin) · #3 27-05-2012, 04:39 PM

Thanks Andrew, pix would be good.I was able to unscrew the Unitron focusser from the end cap.appears to be a thread around 65mm wide. Kevin.

alocky (Andrew lockwood) · #4 27-05-2012, 05:04 PM

Here we go. You want to make sure you get enough backfocus in the system after you add in a 2" diagonal. The ring in the middle of mine is an unecessary complication introduced by the fact that either I wasn't clear enough in my instructions, or the machinist wasn't listening very carefully.
cheers,
Andrew.