The focuser on the ETX70 works by moving the objective along the barrel. Turning the focuser clockwise shortens the barrel and moves the objective closer to the eyepieces. So if you move the focuser clockwise, and then pull an eyepiece out of the holder, you will regain focus.
Because closer objects naturally focus further away from the objective, if you are in focus at infinity and want to focus on something closer to the telescope, you need to pull the eyepiece out by turning the screw anticlockwise.
If you are fully anticlockwise and still not in focus, you could use an extender. If you are fully clockwise and not in focus you are stuffed……
All three of the supplied MA eyepieces 26mm 12mm and 4mm are approximately parfocal, but beware that if the silver barrel doesn’t allow the eyepiece to fit all the way in, you won’t be able to take advantage of that.
The supplied 3x barlow needs to be closer in than the eyepieces, so when you put the barlow in you need to turn the screw further clockwise. If you then remove the barlow, you can get focus by sticking the eyepiece out of the holder. The separate 5x barlow needs to be even closer in, but that’s possibly because the holder sticks out too far….
The best way to find something is to use the 26mm eyepiece first. If you then plan to use the 3x barlow, you should have it sticking out by 5.5mm. For the 5x it’s 15mm. And for the altair webcam with the extension piece on it’s roughly 11mm.
FOV and magnification: The FOV of the 25 and 12mm is about 40deg, For the 4mm it’s about 30deg. The effective magnification is 25mm= 14, 12mm= 29, 4mm=87.5 Multiply by 3 or 5 with the barlows.
