PST Issues

[AstroTiger]

Hi guys

I think after the lovely talk given by Nick Howes at Salisbury, many of us realised that some of our ongoing issues with the PST was down to an internal fault.

Nick advises the correction is easy, however i dont fancy messing with a £500 bit of hardware without knowing exactly what i am doing.

That said, i have had my PST apart this afternoon, and now realise the issues i was having all along with my PST are that the internal prism is not aligned.

Hence why i cannot focus and image with a webcam (its only taken me over 2 years to find this out!)

Right, assuming there are others with the same issue and given the fact that i also need further advise, i have taken a snap of the inerds of my PST with the cover off

Note how the prism is indeed not parallel with the eyepiece.

This is hence why even though i can see the sun at lower mag, the instrument is out of alignment for toucam work.

Could anyone advise as to the best way of removing this prism so it can be reseated, and with which type of glue.

Also do we need to remove the velcro bit?

Any help greatfully appreciated.

Al

[Andrew1972]

I have a PST and with regards imaging I have not been able to reach focus, including using a barlow, but have always been told this is down to the design (in other words they'd probably rather you bought the more expnsive Solarmax 40 if imaging is your thing!). I have heard stories of some being able to reach focus with a standard PST, but this was apparently down to them being lucky buying a 'rare' suitable PST. If there is a way of tweaking a standard PST to reach focus i'd be very interested in knowing.

Andrew

[NickH]

Ok..

They (Coronado)...changed the design on the PST, and modified the position of the secondary filters on the EP tube, which made it impossible to mod for focus properly...(nice one Coronado...thanks for that), this was as part of the "rust" fix which moved the blocking filter.

To get focus on an unmodified new PST you need a short stubby nosepiece adapter for the toucam, which Telescope House can provide. This will solve the focus issue...

But...you're right, the prism is out of line...

Super-glue is the best way, but make sure you position it correctly before doing that,,, as it's irreversable...

[NickH]

can youy get that shot in focus, cua it also looks like you have rust on the secondary blocking filter :-(

[Psychobilly]

Superglue - the bog standard Cyano-acrylate stuff has go a habit of out gasing and the fumes forming white deposits on any figer prints or moisture present so don't close anything up for a while after using it... Low out gasing optical grades are available but they are a hell of a lot more expensive...and you wont find them on the shelf at B&Q...

Peter...

[NickH]

Aye...good tip Peter

[Merlin66]

You can re-align the penta prism and just re-glue to the movement arm with contact adhesive. Not as permanent as super glue but may then allow to check out the performance before you make that ultimate step.

I've just done another PST mod in Melbourne, Australia and found that the prism was mis-aligned in BOTH axis! Not square to the eyepiece in the side view and when you looked at it from the eyepiece end is was also tilted to the LHS!!!

Your pre-blocking filter, as Nick mentions, definately looks like it has a problem!!! If you purchased the unit and still have the original receipts it should be covered by Coronado's 5 year warranty.

[AstroTiger]

Thanks for the feedback ppl.

I sent an email to BC&F i may well see if it can be sent to them for repair.

If not i'll glue the instrument then perhaps sell it.