the one that came with my super cheap telescope is so bad its unusable.
slotting an eyepiece in and using it with no diagonal i can get right up to the maximum magnification I can throw at it! and the image quality is still usable. 119x with a 70mm F5.1 refractor 36$ telescope
the
I used some super thin cardboard rectanges as spacers to space out the lens elements of the telescope. the plastic ring spacer it came with was excessively thick and also broken causing a severe blurring at the edges of the image. but now its almost perfect.
its very disappointing with the diagonal. I can see the image is distorted and blurry like its not a flat mirror.
I'm thinking a decent 45 degree diagonals would be miles better since they are much thicker and shouldn't have any problems with a distorted or warped mirror. and they also make the image upright and correct orientation too.
Also opinions on H-Beta filter? im thinking of getting one as ive read it works the best for orion nebula and other nebulas.