I saw Mercury for the first time in my life tonight, and I actually have a clear view from my driveway ! Furthermore, the Clear and Dark Sky website predicts that I will have a chance to image it in Good seeing on Friday. I plan on imaging it at f/15 with a 2.3um mono sensor, but I’m not sure which filter to use? Is it best to go for max SNR/Min frame rate for lucky imaging or maximum resolution?
Thanks for any advice you can give me.
Generally, I've found longpass filters a better choice than bandpass filters. In good seeing, I prefer the Baader 610 LP and in fair seeing the 685LP. The Astronomik 742 results in a stable enough image in somewhat rougher seeing. The deeper LP filters like the Astronomik 807LP work too, but any additional steadiness they offer is usually offset by the necessarily longer exposures and the lower resolution of the longer wavelengths. I expect that the best bandpass filter may be the Astronomik 642, which is a 642-842 bandpass filter--- I bought one a few years ago, but haven't made any Mercury attempts since I received it. I have used R bandpass filters in the past like the Astrodon R (both e and i versions), but the Baader 610 gives similar resolution with more light to work with thus lower gain setting.
My avatar was shot with an Astronomik 742 in late 2008. In the years that followed I basically abandoned the consistency of the 742 and relied on the 685 and 610LP filters which in moments of good seeing can result in noticeably better resolution as my goals had shifted from just getting a good image to taking a chance to get the best possible resolution. Experience with your conditions and quite simply your current filter choices are the best guide here. In the end, the typical seeing you'll encounter will probably mean any choice is a bit of a gamble. It's also a good idea to take as many videos as you can, with perhaps a minor focus tweak after every 2 or 3 videos. Focusing in these conditions can be tough, and I relied on at least 10 videos with a bit of what would best be described as bracket focusing to increase my chances of nailing focus. Best results were with the Sun up and behind trees, with Mercury at least 30 degrees high. You don't want the scope in direct sunlight in order to reduce thermal issues.