Double stacking Lunt CaK modules

Narrowing the FWHM, tuning to the CWL and enlarging the sweet spot are the preferred activity of any solar imager. Trying to obtain the best from my Lunt calcium module and thanks to a suggestions from SolarChat member Bob Yoesle, I decided to purchase a second module to be stacked with the B1200 I used up to now.

Initially I tried to separate the filter from the barrel as this one is mostly hollow and serves only as the attachment for the front blocking filter. The filter mount is blocked in the barrel by three Allen screws but even removing them there was no way to pull out the filter mount as if it were glued in the barrel. I had to use the full barrel of both modules – with only one BF in front of them – attaching each other by means of a converting T ring.

The experiment has indeed been successful, there is a clear difference between the full solar disc imaged with a single module and the one taken through the stacking. The difference is apparent even during the acquisition and becomes striking after the processing.

The mod is expensive – a B1200 module costs about 1700 – 1800 euros – but worth the expense and fully reversible. It is important to select the best blocking assembly between the two as they can give different sharpness. I would recommend not to use fast f/ratios otherwise the BF doesn’t work properly, best results are from f/8-f/9 up that can be obtained either by a focal extender or by reducing the aperture.

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