Coronado PST modification?

[Legin]

I currently have a 40mm Coronado PST. At first I have captured some great images with it. However currently it has major dark patches making it near impossible to actually use at all.

I think this may be due to the focusing component or the etalon being mis-aligned.

In any case I own a small refractor and I a thinking of modifying the PST to use with a refractor.

Any ideas on a good modification tutorial? Is it worth it.

I have actually reviewed a few so far and it all seems a bit straight forward. I understand I would need an energy rejection Filter something like the Baader D-ERF Energy Rejection Filter. To put at the front of the refractor.

However Baader states they will only sell them with the Hydrogen Alpha filters. So anyone know where I can get such a filter by itself? Are their alternatives.

[Saturnine]

Hi Nigel
First off, does the dark patch you mention change shape and / or position when you rotate the etalon tuning ring. By the sound of it the dark patch may be may mean a defect in the coatings. The internal prism focusing system of the PST can move out of alignment so it is worth the time to remove the cover of the black body and check everything is as it should be inside.
I did the PST conversion last year after reading several online tutorials and generous instructions from a fellow IISer, Merlin 66. I purchased an 90mm Baader ERF from TeleskopShop in Germany and explained to them that it was for an PST conversion and had no problem with buying it. Luckily the exchange rate was a bit better at the time but I now wish that I had gotten the next size up, 110mm.
Remember to keep the f ratio at f10 or a bit longer is ok too.

[Merlin66]

Nigel,
Sounds like there may be an "issue" with your PST....
The prism/ focuser can cause problems with contrast/ clarity but not normally as "major dark patches" - this however could be due to a failed ITF filter in the eyepiece holder.
I'm assuming your PST has the "blue" objective.

A good PST makes a good PST mod...a poor PST will cost you money for a mod but will not perform well....
Drop me a PM with your email details and I'll send you a copy of the PST mod write-up.

I would not recommend moving forward with a mod until you can ascertain what is the current problem.