1-2 October 2020 New filter stack layout.

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Friday 1st & 2nd. Cloudy and windy. Easterly sky movements.

Thursday 1st Oct. The seeing was very poor. I rebuilt the filter stack & etalon to better match the PST geometry. 

Friday 2nd Oct. Very cloudy but I am taking a chance of a clearing to test any changes the new layout might achieve. Very long waits between brief clearings. 

15.11 Rather dark but this is my first image today. Still too light in bottom right hand corner. I haven't had a chance to adjust the etalon yet. Just enough time to focus and grab a video in a few seconds. Cropped.

Focuser problem solved. I moved the backplate clamping ring from outside to inside the back plate. The protective filter stack, on its M48 extenders, is clamped by the ring inside the main tube. 

The 2" front spigot, of the helical focuser, screws directly into the filter extensions within the backplate. So there is plenty of support for the cantilevered stack. Focusing is now before the etalon. So no change in etalon to focal plane spacing takes place. 

 15.31 Snatched between clouds. A different presentation with the new layout. Not enough time to determine the seeing. Heavily cropped. I had quickly adjusted the etalon but there was no time to be sure it was optimized.

There follows the usual arrangements of extenders to secure the correct spacing between the PST etalon and the focal plane. I used a hidden grub screw to secure the 1.25" camera spigot into the 2" adapter. This achieved an almost zero, optical length 2"-1.25" adapter.

The focal plane now falls on the shoulder of the camera where the sensor lies inside. GPCs can be fitted and removed simply by removing the camera's 2"-1.25" adapter. Now all I need is some sunshine to check it all works as expected.

As I waited in vain for another clearing I swapped the parts around, yet again. The 2" Baader Clicklock clamp is  now at the rear. One turn of the lever and the Lunt B1200A blocking filter and the ZWO '174 camera are released as a unit. For safe, overnight storage indoors. No 2" to 1.25" adapter required. Very convenient. Pictures of the new set-up tomorrow. Sadly the forecast is cloudy again.

The next image shows the most recent set-up. With the 2" Click-lock clamp in place at the tail end of the etalon/filter stack. The helical focuser is now up against the telescope's back plate.

NOTE: That didn't work either. I had nowhere to fit a GPC to the camera nose. So I have refitted the T2 to 1.25" adjustable adapter. Now I can fit a GPC and independently, fine focus the camera position if need be. Though the camera does rotate with this screw type unit.

Be warned: The Lunt B1200A "straight through" BF needs far more room than the PST blocking filter. The Lunt projects out from a standard 2" receptacle and blocks access to GPCs.

While the PST BF allows a GPC to fit into its top recess and fits snugly into any standard 2" socket. The B1200A is also considerably undersized in diameter, for a 2" push fit. So getting a safe grip on it is always a struggle and needs very careful, double checking. While the smooth exterior of the PST BF just fits and can be gripped without any fuss. 

Just imagine if the Lunt BF fell out of its receptacle during a Meridian flip? It could drop a small fortune in both itself and the costly ZWO '174 camera. Straight onto the observatory floor! Possibly from a great height! Falling further still if it fell through my open trapdoor! So be very careful indeed if you own a Lunt BF! 

You cannot rely on the camera cable to remain attached and support the weight of the combined unit being dropped. You may not even have the camera cable tied off safely. I can't see any easy way to provide a safety lanyard on the BF. Perhaps an eye bolt screwed into the ZWO camera's back plate?

Saturday 3rd is a dark and dismal day with a heavy overcast and NE gales! Not much chance of seeing the sun today!

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