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Sunday 26th 19F, -7C at 08.00 CET. Another cold, sunny day is forecast. A bright, half moon is high in the SSW. There is a large group, of large sunspots, in the south east solar quadrant. [AR2916] A second, less dramatic group lies in the north east quadrant. [AR2918] So I really ought to make an effort today.
The optics are almost certain to dew over when uncovered after another hard frost. The dome warms when the shutters are opened and the interior exposed to the sun's warmth. Meaning that the optics lag behind the rising air temperature leading to condensation. The dew bands will need to be switched on early. Even before the low sun clears all the local obstacles. No doubt I shall need the encouragement of the hair drier. I shall also have to wrap up warm myself!
I have been advised to reduce the number of stacked images I habitually use. Presently 75 out of 500 captured in SharpCap and processed in Autostakkert AS!3. As the advice came from a highly skilled solar imager I really should experiment. His images are often so much better than mine that there is simply no comparison.
Regarding image size I have tended to use the most powerful GPC I can get away with. Depending on the seeing conditions on the day. There is a clear tradeoff between increasing power and a smaller field of view.
Where detail is spread over several fields I could build a mosaic. Rather than using a weaker GPC in the hope of sharper detail and a wider field. Wider fields risk finding the PST etalon's sweet spot. This is a geometric limitation. Where a larger aperture, longer focus lens is used with too small a diameter of etalon. Resulting in a limited spot or ring of better H-alpha detail but with bland areas all around.
Larger aperture etalons cost a lot of money! Hence the number of solar imagers. Who "borrow" the PST etalon from inside a Meade 40mm H-alpha telescope. Then fit the etalon to the H-a filter stack behind larger instruments. In what is known as PST Mod. [Modification] Provided the larger telescope works at f/10, or can be made to do so, the results can be astounding. Though [sadly] etalons vary widely in quality and bandwidth.
There are alternatives but none can be called "budget." Even these devices are open to wide variations in quality despite the very high price tags. Some of these options also have optical or thermal limitations. With long lags for internal heaters to work as intended. Or needing built in Barlows to work at f/30!
Despite the increasing popularity of H-a solar imaging, it is still a narrow interest hobby. Making economies of scale, with volume production, a bit of a non-starter. Only a very few companies are involved in etalon manufacture globally. So market competition is relatively weak. A larger etalon can cost as much as a small car.
All of this information is available online using suitable search terms. Or discussed on generalized, astronomy forums. The largest and most active, specialist, solar forum being SolarChat! Where some of the finest solar images, produced by skilled amateurs, can be seen on almost a daily basis.
There are sub-forums for discussion of instruments, modifications, processing and techniques. The regulars are a friendly bunch and bent on the improvement of instruments and techniques. Rather than cut-throat competition for attention or who can spend the most. Some skill and experience is required before even the most costly equipment will perform.
Every imager and observer is limited by the seeing conditions on the day. Those who live nearest the equator are not guaranteed improved seeing conditions. Their reduced path length of atmosphere, with the sun usually high overhead, may suffer thermally unstable air. While those languishing in the far north. Can enjoy moments of fine seeing provided the sun is actually above the horizon, or above local obstacles.
Imagers and observers carry out their work/hobby in widely varying conditions. From balconies on high rise buildings. Or from their gardens in cities completely surrounded in city buildings. A little direct experience will tell. Whether a certain location enjoys suitable seeing condition. Often enough, to make the investment in time and equipment worthwhile. There seem to be no hard and fast rules.
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