I have always wanted to capture the ISS crossing the sun. This first attempt was captured on the 30th of November with the ISS and sunspots clearly visible. To workout the position I used an app called "ISS Transit prediction" (https://play.google.com/store/apps/details?id=com.ed_morana.iss_transit_prediction_free&hl=en) to find out where the transit will occur. This app produces a prediction map and text if there is a transit in your area.
The shot was taken through my 80mm Vixen refractor with a solar film filter (NB: goes without saying, do not ever look at the sun WITHOUT A GOOD SOLAR FILTER - Ed) and a ZWO ASI 120MC camera. Tracking was on my Ioptron ZEQ25 which was just roughly aligned by pointing and leveling after telling it to goto the Sun (www.ioptron.com/product-p/3322.htm ). I needed a focal reducer spaced with 2 neutral density filters to get a full screen image and the shutter speed correct. Then used "FireCapture" to record a video timed for 1 minute either side of the predicted transit. Firecapture was running at 30fps. Only 18 frames had the ISS which is less than 1 second for the transit.
I trimmed the video and saved the individual frames with Virtualdub (http://www.virtualdub.org). Can also save a slowed video with Virtualdub.
I then used a programme called StarStax (http://www.markus-enzweiler.de/software/software.html) to stack the frames which can either stack white things (i.e. stars) or black things (i.e. the space station against sun). It will also do a progressive stack so you can make a video of the ISS progress across the sun. I used the "makeavi" function to create a video from the stacked frames. The file needs a little more work as it has some dust bunnies which I should remove with a flat.
Ron subsequently cleaned the immage up to remove the dust bunnies. Compare this image with the earlier one to see the benefit of flat fielding.