Stacking a Pair Coronado 90ii Etalons
Posted 01 June 2020 - 09:40 PM
Recently purchased a pair of Coronado 90ii etalons with Richview tuners. What is the proper technique of first single stack viewing with Richview tuner and T-max? Also the procedure of double stacking? Using BF30 and TMB 100 f/8 .
What is the purpose of Richview tuner?
Posted 02 June 2020 - 10:41 AM
The richview mechanism compresses the etalon *slightly* changing the separation between the etalon plates and therefore shifting the center wavelength.
You may need to relocate the silver pin that limits rotation, but don't rush into it just yet.
A tracking mount, assistant and camera will make this a breeze but are not required.
First half: adjust your etalons. For each etalon do the following in single stack
-Adjust the tilt until the reflection is away from the solar disc. Use the minimum tilt necessary.
-Adjust the richview mechanism until you get most contrast. A camera with histogram works nicely. The etalon is tuned when the image becomes darkest. The brightness will reach a plateau, use the least amount of tightening required to get there. An alternative is to visually look for the most contrast instead of the histogram.
-Relocate the silver pin if necessary.
Second half: Tune the double stack
-Place the first etalon, give it enough tilt to get rid of the reflection and then use the richview mechanism for maximum contrast.
-Tape down the tilt tunner wheel and tape a reference for the richview setting.
-Place the second etalon.
-Give it enough tilt to move the reflection out of the solar disk. Use the minimum tilt necessary. Tape the tilt tunner wheel.
-Use the second etalon's richview tunning mechanism. This time you want the image to become the brightest possible (this happens when both transmission peaks match). Same rules apply about the plateau and using the least force necessary.
-Mark the reference position for the second richview tunner and you're done.
In the future your tune will be very close to this position and will mostly change with altitude. That's why I recommend the tape to get you close without much fuss. The richview reference is the most important. You can adjust the tilt by simply watching the reflections move.
Please keep us posted. I'm very curious of your results. I've never seen double richview etalons stacked even though the sales brochure mention the possibility.
Posted 02 June 2020 - 02:40 PM
In the double stacking mode, do you adjust the second etalon with the first etalon nearest telescope objective attach to the scope?
Posted 02 June 2020 - 06:01 PM
I apologize if it wasn't clear. Let me try again.
For double stacking you first adjust one etalon by itself. Once you know it is tuned you leave it alone. This etalon will remain closest to the objective. Let's call it etalon A.
Once you know etalon A is on band you add etalon B. Etalon B goes on top of A. Make sure you don't change A's tuning when screwing etalon B in place.
It is possible to tune both etalons at the same time but it takes some practice. Your setup is particularly tricky as any change to A's settings will alter the tilt of B. That's why I recommend you do it one at a time.
The marks are to get you a close starting position the next time out.
Posted 02 June 2020 - 08:52 PM
Will try this weekend . It’s looks to be sunny