Imaging Technique to attain on band HA and full illumination

[Nigella Bryant]

Hi all, 

After promising this tutorial a few weeks ago, I've just got time to get to grips with this and hopefully help others. I've developed my skills with image acquisition and processing over the last year since acquiring my Lunt  60mm DS.

Attaining on band is crucial to gain detailed images and to get the most out of a HA telescope. It had come to my attention after looking at images taken near the same time as mine with the same equipment and seeing that these images had shown a lot less detail or no detail than what I have become accustomed to even if the disc is not particularly active.

So this is my usual work flow when first setting up the Lunt telescope for HA observation and imaging. I tend to use a laptop to observe electronically and image.  It fascinates me after an imaging session just to sit and look at the sun on the computer screen and zoom in on various features that I see. The acquisition software that I use is Sharpcap. 

So after setting up the Lunt on the mount (Skywatcher SolarQuest Mount and EQ6 tripod) I attach my Zwo Asi 178mm. 

1. First get the best focus that you can, this is critical and I zoom in and out to find the optimum point. I then usually acquire my first avi file just in case the clouds roll in. Then I fine tune the Lunt a little to see if I can tweak a little more detail from adjusting the tuning and tilt tuner on the double stack. I have also found that the telescope appears to be optimum after thirty minutes (I assume this is because of the telescope blocking filter becoming warmed up to the outside temperature). 

2. The image on the screen/in the eyepiece is often not quit on band or the illumination is not quit right. Dealing with the on banding is achieved by both tuning the Lunt (pressure tuned model) by turning the pressure tuner inwards (I usually unwind this after each session) until features become evident. This in turn affects the illumination and is sometimes not centred. Tune with the tuner and also if double stacked move the dial on the double stack unit until illumination is centred. I usually have the disk slightly over exposed so I can see the shift of illumination from the tuning and tilt adjustment as per screen shot in image 1 and 2 (I never take off the double stack unit).  I don't always get this right, particularly if clouds are rolling in and I need to be quick to acquire data. 

3. Full illumination is beneficial so you don't have to take flats because the image is illuminated across the image with no bright spots. This also benefits when you come to process the image and makes processing much easier as you don't have to fight uneven illumination. 

Hope this helps. 

 

Edited July 1, 2020 by Nigella Bryant
pic added

[richard ashbee]

Thanks Nigella, Very helpful, keep them coming

[Pete Presland]

Excellent tutorial, thank you for your time and effort Nigella.