Heavy modifications to the 200mm f/3.52 dob's upper cage.
The telecope can now be considered done after a significant ergonomic rework of the whole upper cage.
The main changes are :
- addition of a strock-like spider hub, making secondary collimation the breeze it should be
- addition of a filter slide & filter holder, that allowed me to find a nice 52mm astronomik UHC filter
- addition of Marcosatm’s crayford focuser to handle heavy loads better
- addition of a tuneable coma corrector holder, allowing me to set the correct backfocus once and leave the corrector alone afterwards
- addition of my friend EleusisT’s fantastic fully printed 1:10 crayford reducer
The spider hub
Thought as a drop-in replacement for the previous spider hub, this one steals the great ideas from the strock telescope, and replaces a push-pull system by pushing against puller springs. No modification of the upper cage was needed for this mod.
The filter slide
An additive modification too : a slide with indexing steel screws slides up and down, and is stopped in position by strong indexer magnets.
The corrector holder
The corrector holder goes inside the focuser from the inside of the upper cage. It has 5mm of total travel, allowing for fine setting of the backfocus once. The corrector protrudes inside the focuser’s drawtube, modified to add a bit of lateral clearance.
The 1:10 reducer
Assembled with care, this reducer gives smooth fine motion at a ridiculous cost. Detailed assembly instructions can be seen here on Printables : https://www.printables.com/fr/model/501591-crayford-focuser-reducer-110
The flexible attachment to the UTA absorbs any assembly imprecision and guarantees a smooth movement free of locking points.
The only challenge is the print precisions of the two planetary reducers inside it. We have had fairly good success with 0.3mm nozzles.
Full assembly
Even though a bit busy, I’m happy with the compactness of the whole focuser-corrector-filters system.
