Get the best performance possible from your Lunt single-stacked or double-stacked pressure-tuned solar scope.
So, you have gotten yourself one of those beautiful pressure-tuned solar scopes (like the Lunt LS80T) with all its knobs and you’re wondering…how on earth do I drive it? Well, this is my way! The first step is to stick it on a mount and point it at the Sun. Most of you should have gotten that far by yourself, but if I didn’t mention it someone might complain. 🙂
How I do it
Note: This tutorial works for both a single-stacked and double-stacked Lunt telescope!
Step 1: Unscrew the large etalon knobs
You want to back each etalon knob right off until they pop or hiss. Don’t worry if they come right off. They are a bit fiddly to screw back on, but I find winding them anti-clockwise until you find the knob falls into the end of the thread then winding clockwise works the best.
Step 2: Set up the scope in single-stacked mode
Remove the double-stack unit, and don’t forget to replace the spacer between the etalon and the focuser! (Ignore this step for single-stacked telescopes) [Figure 1]
Step 3: Roughly focus the scope
If it won’t come into focus you can loosen the blocking filter screws and move the filter in and out until focus is achieved. The Sun will most likely look like a featureless disk at this point. [Figure 2]
Step 4: Wind the tuning knob inwards until surface detail appears
If you have a camera attached the histogram will conveniently show a minimum at the best tuning point. FireCapture’s horizontal histogram bar is an excellent tuning aid. [Figure 3]
Step 5: Refit the double-stack unit
Replace the double-stack unit, and remember to remove the spacer. (Skip this step for single-stacked telescopes.)
Step 6: Focus and adjust the double-stack unit
Adjust focus on the double-stack unit until more surface detail appears on the Sun. With a camera in FireCapture, this corresponds to a maximum on the histogram. (Skip this step for single-stacked telescopes.) [Figure 4]
Step 7: Mark your settings
If you put a pen mark on both etalon knobs this will give you a starting point for next time. The tuning won’t be exactly the same, but this gives you a starting point. After a few successful tunings you will get the hang of it and find that the double stack unit doesn’t need to be removed. Simply fine tuning around your initial pen marks will work.
For visual observers, you can stop here!
An additional note for imagers
If you are using a camera, tuning on the histogram for the single-stack etalon will not work if the double stack is installed. I just wind the single stack tuner both ways until features disappear then adjust it to the mid point. Then tune the double stack with the histogram.
If you increase the gain on the camera, you will find a hot spot. It’s something that occurs with a double stacked unit. [Figure 5]
I find fine tuning both etalons slightly until the hot spot is centered will give a better image and be less problematic when doing mosaics. [Figure 6]