When using 90 degree star diagonal, image is blurry.

[MBErdogan]

Hello guys,

 

 

I have just bought the celestron powerseeker 50az, I mounted everything correctly. At night when I look at the moon, when I don't use the 90 degree star diagonal, I can see the moon perfectly sharp. But when I use the 90 degree star diagonal, the moon gets very blurry; I cannot get a sharp image, I tried everything. How to fix?

[John]

Have you adjusted the focus to account for the change that the diagonal causes ?. Usually using a diagonal will require you to move the focuser tube inwards 50mm-70mm approx to reach sharp focus again.

 

Edited December 27, 2020 by John

[MBErdogan]

Yes, i tried everything

[fifeskies]

Have you checked the mirror in the diagonal

Very occasionally new mirrors have a protective film on them that should have been peeled off before delivery.

Or perhaps it has been smudged with some oily residue and needs wiped clean.

 

[John]

If the scope focuses sharply without the diagonal in place and the diagonal is the only change between that and not being able to get sharp focus, even after adjusting the focus, then the prime suspect becomes the diagonal. It is possible that the mirror of the diagonal is out of position, ie: not at exactly 90 degrees to the light coming down the scope ?

If you bought the scope new, you should really take it up with the vendor and see if they will supply a replacement diagonal.

If the scope was bought used and the diagonal is faulty, you can buy replacements.

I assume that this is your scope ?:

The mirror diagonal with these is pretty basic so it is quite possible that the mirror has come loose.

 

 

[MBErdogan]

Which 90 degree star diagonal would you suggest me to buy? I would like one which is a little more qualitatively.

Edited December 28, 2020 by MBErdogan

[fifeskies]

The well known auction site has some basic diagonals at low cost , but you will need to wait a few weeks for it to arrive.

PowerSeeker 50AZ Telescope | Celestron

according to this page you need the small 0.96 inch diagonal

but check this before ordering , this is not a common size except on the smallest telescopes.

[John]

If it is a .965 inch diagonal your choices will be very limited I fear. Check that first. If the scope uses 1.25 inch then your choices are very wide indeed.

Presumably the scope was purchased used then ?

 

 

Edited December 28, 2020 by John

[MBErdogan]

Nope, brand new

[Ricochet]

If the diagonal really is a 0.965" fitting, then I would use the excuse that it it is broken to return the entire telescope for a refund. You can then put the funds towards the cost of a larger, better telescope that uses standard 1.25" accessories. 

[MBErdogan]

What do you think of the Bresser Messier NT-150L/1200 EXOS2?

[Ricochet]

It will be a much, much better telescope than your current one. The only downsides are that it will also be much heavier, which potentially could put you off from using it, and that when you have a Newtonian on an equatorial mount, you will have to stop to rotate the tube in the rings when you move to a new object or the focuser can end up in positions that are difficult to use. 

[DaveL59]

I wonder if it is indeed a mirror diagonal or perhaps a prism one?

Does the diagonal give good views in daylight and right way up?

Edited December 28, 2020 by DaveL59