M27.
M27 on 06/09/1999 with my 190/200/760 FFC and ST7, 15 m exposure.
This picture was made on 4 september 1999 with my 250 mm F=3750 mm SCT and ST-7a. 10 exposures of 5 m each at -5° C and 2x2 binning were added. Carefull analysis shows that the image is not perfectly focussed and the sky conditions were not that good as well. Also the magnification is a bit too high for this object, but it was an instructive exercise...
Well, not one of my best images ! Sadly, the hypered TP2415 shows "mottling" on both sides of the negative. After a long search for the cause of this, it was established that this phenomenon occurs only with bulk 2415 film (reels of 45 m). The film is very tightly wound, putting high pressure on the emulsion, and shows this effect after hypering. Regular 135 mm film in 36 exp. cassettes never shows this effect. I am not the only amateur to have encountered this. Only after a few other amateurs noted this phenomenon (Marco De Bellis, Martin Germano, Preston Justis, Hubert Degroote) and after a full report to Kodak by Marco De Bellis did Kodak recognize early september 1999 that there was a problem worth looking after !
Now for the photo details : 22/07/1995, 250 mm f/15 SCT, exposure of 75 minutes, guided with ST-4 on a 90 mm f/11 refractor.