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If the focus is not changing when you move the knobs it may be that the small adjustment screw that locks the focus has been turned by accident (I've done this myself).  If this is moved to the point where it 'bites' no amount of twiddling the knobs will shift the focus, so have a look and see if there is a small screw that doesn't hold one of the focus tubes in place and back this off.  It might help.  I twisted mine by accident in the dark whilst placing the focus tubes and it caused me no end of problems until I got it loose again.

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Ive managed to focus so that the stars became smaller and brighter, but what i saw was more like small streaks of light, not spherical dots.

im using the tube extension, so it seems that im able to achive focus, the problem is more knowing when im at perfect focus.

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33 minutes ago, FarAndBeyond said:

Ive managed to focus so that the stars became smaller and brighter, but what i saw was more like small streaks of light, not spherical dots.

im using the tube extension, so it seems that im able to achive focus, the problem is more knowing when im at perfect focus.

Do the streaks of light all point in exactly the same direction and flip through 90° when you go through the point of best focus? If so you have some astigmatism in the system.

You could also be seeing coma, which is inherent in Newtonians with parabolic primary mirrors. When correctly collimated, the central stars will be points and the outer stars will all point to the centre. If the collimation is out then the point like section may be offset. Look around the edges to see is there is a section that is (more) point like.

Finally, the secondary mirror support vanes will create diffraction spikes. On your telescope these should show as a cross, but only the brightest stars should show this.

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When properly focussed only planets should resolve as spherical dots.  Stars are more like a white point of light looking very much in the focussed EP rather like you'd see them with the naked eye.  

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