In the 1980's I collected antique Clark Refractors. Here are two six inchers, and a five inch, dating from 1887, 1888, and 1889. Their image sharpness was sometimes used to visually estimate variable star brightness.
Walter Scott Houston proudly showed me his 4" clark refractor that he used to make the many wonderful observations for years described in his monthly column "Deep-Sky Wonders" for Sky and Telescope Magazine. He also was an avid variable star observer for the The American Association of Variable Star Observers (AAVSO).
These are 30 and 40 second exposures taken a month apart between November and December 1998 of IR Gem, a variable star found in the constellation of Gemini the Twins. It shows the dramatic change in brightness from outburst to quinescence. At low light state the exposures even had to be increased to 40 seconds or the variable wouldn't have shown!
I use a 12" LX-200 computerized Meadescope and an SBIG St-6 CCD camera to do time-resolved photometry of cataclysmic variable stars for Dr. Robertson at Arkansas Tech University and Joe Patterson of CBA at Columbia University.
This is an artist's concept of a cataclysmic binary star system. The normal low mass star at upper left is in orbit about a more massive, but much smaller, white dwarf star, which is situated at the center of the disk of material to the lower right. The stars are in such a close orbit, and the gravity of the white dwarf star is so strong, that material escaping from the normal star is captured by the white dwarf. This material, which has angular momentum, swirls in onto the white dwarf, forming a flat, rotating disk. The material in this disk heats up to temperatures of tens of thousands of degrees, emitting strongly at ultraviolet wavelengths. HUT astronomers will try and understand the complex processes that occur in these star systems. (Image courtesy of Dana Berry and the Astronomical Visualization Laboratory at the Space Telescope Science Institute.)
SS Cygni is in the constellation Cygnus the Swan. It is a cataclysmic variable star. (Thanks to http://hou.lbl.gov/~vhoette/Explorations/SSCyg for the info about this particular star.)
Cataclysmic variable star V1309 Orionis in outburst showing super humps and a deep eclipse in its light curve. Data obtained with a SBIG ST-6 CCD camera and 12" telescope at Whispering Pine Observatory. Multiple images were taken over the course of several hours. Photometry reduction done by Dr. Jeff Robertson at ATU using the Munidos program running on Linux.