Ghosting on Coronado PST

[trent_julie]

Hello all,
I am having trouble with my Coronado PST when I double stack it. What seems to happen is a ghost image of the sun appears, this wouldn't be a problem ordinarily but it manifests itself right at the most ideal tuning point.

I am wondering if anyone else has run into this problem, and what steps they took to resolve the issue. I have heard that removing the ERF can help, but this seems like extreme surgery.

Thanks in advance.

Trent

[MikeyB]

If the ghosting happens at "the most ideal tuning point", you are tuning the two etalons in the wrong order.

Correct double-stack set-up procedure is to tune the front (SM40 external, tilt-tuned) etalon first, so as to put the ghost (internal reflected) image outside the field of view. Pay no attention to solar features at this stage - just get rid of the ghost image.

Then the rear (internal, PST) etalon is tuned to provide optimum viewing of solar features and the brightest image. This setting may well be different from the normal single-stack position of the internal etalon. As solar features will be much more apparent with the double-stacked scope, the ideal tuning point is likely to cover a wider range than previously.