Parfocal rings

[starklutz]

using a Meade EXT125 with a QHY 5-III 178C camera. Able to view moon, Jupiter, and Saturn on laptop, but focus isn't very sharp. Focus with eyepieces are OK, just can't seem to get near as sharp a focus with camera using laptop. Without sounding real dumb, what are the included parfocal rings for and how are they used?  Do I need to experiment with these to try and get a sharp focus using the camera?

[RT65CB-SWL]

Hi @starklutz and welcome to SGL. 

A parfocal ring simply attaches to the nosepiece of your chosen e/p's and held in place with a grub screw or set screw. Some e/p brands are parfocal throughout the series, i.e. TeleVue Plossl's... e.g. they are particular useful if you have Plossl e/p's of different brands and saves having to re-tune the focus if there is a big difference where they reach focus.

If it is say <1mm then no need to use one, but at >4mm then parfocal rings may prove useful.

Out of interest, which port of your ETX125 are you using? - I found there was a focus difference between the rear port for the visual back and the e/p port on top of my ETX105, before I re-modded it and a parfocal ring helped.

Edited August 18, 2020 by Philip R