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B&L Criterion 4000 SCT focuser issue

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#1 Shelldrake

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Posted 20 November 2019 - 06:47 PM

Yesterday I purchased a gently used B&L Criterion 4000 SCT and seem to have been fortunate enough to get one of the few examples with decent optics. However, the focuser assembly is pushed out of the OTA by the weight of the mirror when the OTA is anywhere near vertical, exposing the screw linkage (see attached photos) and causing the scope to lose focus. Any thoughts on how to fix this issue? Thanks! 

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#2 Karl Fabian

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Posted 20 November 2019 - 09:18 PM

The nut that is on the focus knob with the nylon washer is installed incorrectly. Grasp and hold the knob and loosen the nut turning clockwise. You should then be able to unscrew the knob (counterclockwise) from the threaded focuser shaft. Likewise unscrew the nut from shaft.(Be careful not to push the threaded shaft forward into the scope while nut and knob is removed!) Now put the white nylon washer on the focuser shaft up all the way up where shaft comes out of scope and then thread the nut up all the way against the nylon washer. Tighten nut with fingers only enough so when you pull and push on the threaded focuser shaft there is little or no end play. Then thread the  knob back on until it abuts the nut  Then you will need a thin open end wrench to tighten the nut up against the knob to lock the knob on place. Hope this helps.


Edited by Karl Fabian, 20 November 2019 - 09:34 PM.

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#3 Shelldrake

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Posted 20 November 2019 - 09:35 PM

Thanks Karl!


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#4 Karl Fabian

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Posted 20 November 2019 - 10:28 PM

No problem. Glad I could help.



#5 Shelldrake

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Posted 24 November 2019 - 12:38 PM

Once I got the focuser sorted out and cleaned the corrector plate (the visual back had been left open for who knows how many years), I was able to take advantage of the clear sky last night and try out this little 4" SCT. Collimation was decent if not spot on so I left it alone for now as stars were still pin point sharp. With the 18mm EP I was able to resolve all 4 stars of the Trapezium in M42, which leads me to believe that the optics are better than average for a Criterion 4000. 




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