Friday, 8 August 2014
Western Active Regions Ha Closeup
For some time now I have had my suspicions that the performance of my PST mod was being limited by the etalon not being truly collimated to the optical axis of the donor OTA, despite upgrading the focuser on the Tal100R to a nice Moonlite unit, when then is another focuser hanging off the back of this it does incur some flexure in the system. Not even noticeable if you were using the scope as intended, but in solar astronomy where the slightest tilt of an etalon affects it's performance this is crucial. I was getting some banding previously on images with this setup, which is usually a sign the etalon was being tilted too much (sag due to flexure), so I decided a radical approach was needed. I completely ditched the second focuser and just used extension tubes to get the camera chip the required 200mm behind the refocusing lens in the etalon assembly. As soon as I did this I could see a marked improvement in terms of an increase in detail and contrast, without the adverse effects of banding. By doing this has reduced the loading on the Moonlite on the Tal by some 80%. Now the next job is to work out the optimal rotational clocking of the etalon with the OTA, and then the same for the blocking filter with respect to the etalon. When all this is done it will be index marked to ensure quick repeatability.
Posted by Mark Townley at Friday, August 08, 2014