Issues in a C5 PST configuration

First issue: two picture says it all, it's internal reflection. The strong sun light after passing through the Cheapy ERF, is still strong enough when it comes to the SCT corrector, and then light is reflected again by the ERF, creating a secondary ghost image. Another source of secondary reflection is that, light going to PST etalon is reflected partially back to the SCT secondary mirror, to create another ghost again.




Yes, it's internal reflection. You can clearly see the shadow of the secondary, right?

It's even worst at first, but I managed to tilt up the ERF in order to kick the reflection out of view a little bit more. But it's there still. The tuner in the PST etalon module does help a bit more, but still, it's still there.

Need to find better way, or else contrast really suffers.

Such effect is best demonstrated by the histogram, all the signal is on the right side, without any signal at the left... similar problem in white light can be seen and thus, I guess the reflection from PST etalon is not as big as the one from Cheapy ERF and SCT corrector:



Second issue is newton's ring:-