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Coronado PST focus


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I acquired a second hand Coronado PST. The focus knob doesn't seem to have any effect on the image and, although it turns, it feels as if something inside the scope is "slipping".

Is it worth opening up and taking a look to see the focus knob in action?

Is there anywhere that services the PST without sending it outside the UK?

Are there any nasty surprises if I open it up (springs, pressure points etc)?

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Seeing as it’s likely out of warranty it can’t hurt to take a look.

The PST uses a 5-sided prism to bounce the light up to the eyepiece. One face should be parallel with the front on the scope, one with the eyepiece. When you’re turning the focuser you’re just screwing the prism holder back and forth within the black box.

The holder isn’t a great design. The prism is “pinched”, if you will, at the slides (like a litter picking claw might pinch some rubbish). It’s not a great way of securing something so it’s not unknown for the prism to slip a little which puts the whole optical alignment out of kilter.

Have a go at unbolting the hex bolts on the side of the black box and see what you find. They might be a bit stiff - I think mine were loctited. It could just be a case of manually adjusting the the prism so it’s facing the correct way in its cradle.

Good luck.

Edited by hunterknox
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