Buying a high quality interferential filter is a huge investment, similar to the one of a good small scope. As no amateur can really buy such an accessory, manufacturers have built various cheaper models providing in spite of everything excellents results. 1.5 H a filter which will show you prominences in all their splendor. But its aperture is only 40 mm which limits the resolution of disk detail substantially. At left the Lumicon and Thousand Oaks H-alpha 1.5 filters are the same product.
Models differ by modes of tuning and by spectral uniformity.
The University serie for example uses finest components, is thermally tuned by a calibrated precision oven and is the most expensive model. But it displays images of top quality. The regulation of the oven temperature is manually adjustable by moving the tilt of the filter which changes the optical path length through the filter. The temperature regulation stays however an important factor using Daystar filters. You could only use our filter no more than 20 minutes, sometimes less depending the cold intensity, then the bandpass will go off and you will start to loss detail, mostly surface.