Problem with PST or...?

[04Stefan07]

I tested out my PST CaK today and was unable to get the Sun into focus.

When focusing it there seemed to be no pressure on the turning knob, I got a feeling the focuser is broken.

No matter which way I focused I got the below image as a result.

[jjjnettie]

What were your camera settings? Was the gain set too high and blowing out the image?
Just putting it out there, sometimes it's something simple.

[04Stefan07]

Yeah I was thinking the same as well!

All those settings looked alright.

[thunderchildobs]

Did you actually look through the scope?
If you can not get focus visually, then you got a broken focuser.
Otherwise the camera settings are wrong or the scope with the camera cannot reach focus.

Brendan

[sheeny]

Test it visually. You should be able to get focus visually - if not then your focuser is broken.

A camera is a different matter. The standard PST is difficult to achieve focus with an astro/web camera without a short nose piece or a barlow lens (only - not the extension tube) fitted to the nose piece. A DSLR camera will have the focal plane even further back I suggest.

Al.

[Merlin66]

Unless you have the eyes of a ten year old, it's very difficult to see much at the CaK wavelength...
I'd remove the side cover from the black box and check if the focusing pentaprism is moving with the focus knob.

[UniPol]

If you decide to remove the side cover as Ken suggests, check that the prism is at right angles to the light path as it is only held on with silastic and can move over time. The side plate cap screws can be a bother to remove as they are usually "loctited". I'd suggest jerking the allen key rather quickly in the anti-clockwise direction to break the bond.

[N1]

Hi Stefan, I don't own a PST, only a Halpha Solarmax filter set, so this is a wild guess. But I did have a similar experience and it's from the same producer. When I first got the filter set and gave it first light, I thought it was broken until I discovered that I was looking at a ghost image, which was featureless, blurry and impossible to focus. In the Solarmax, the ghosts are many degrees from the actual image, so are not in the same FOV. I know this sounds stupid, but when I made sure the telescope pointed at the Sun, and not just somewhere near it, the problem was solved.

[trent_julie]

I would guess that the prism has detached from the focusing screw. Do a google image search for "coronado pst prism" to see images of the optical assembly.

[04Stefan07]

Yep, I can just see the Sun through the telescope but it was hard to tell if it was focusing or not due to how dim it is.

[04Stefan07]

As always very helpful suggestions were mentioned and I will give them a go and report back with my findings.

Thank you!

[04Stefan07]

Ok I have some good news!

I detached the panel from the side and the prism looks to be moving up and down as I turn the focus knob.

[Merlin66]

OK, that's promising...
Are you using the DMK? Is it fitted with a short nosepiece (with no shoulder)?
It needs to sit right down into the eyepiece holder to get close to focus.
Play with the gain settings to see if the image is just over-exposed....

[04Stefan07]

I am using the QHY which has no problems focusing (the main reason I bought that camera).

Check out the image below of the prism.

[Merlin66]

I assume it focuses OK in the Ha PST.....
I'd try different gain and exposure settings first........

[04Stefan07]

Yep looked alright in the Ha.

I will give it a go next time the Sun is out :).

Thanks!