Posted by Andrea Tasselli at 18:09 on 2011 May 12
Hi Martin,First off analemmas as best created with cameralens as the field of view required is normally far too large for most scopes. Depending on the lens choice this will severely restricted the size of the sun disc on the image. If you won’t use filters (such as baader’s astrosolar) than you should aim at taking the sun’s shots fairly low on the horizon and use the shortest exposures @ f/22. ISO could be around 200. Using filters you’d probably need to open up the lens quite a bit and adjust exposure as required. I’d keep ISO as low/high as required. Just experiment a bit and you’ll find the right combo.Now for the second question. You’d need either to clamp down the camera or the camera tripod (assuming you can move the camera in and out of the tripod without disturbing the aim) for a whole year or you need to have a reference in the field of view that won’t move for a year and a way to exactly match the position of the reference object before taking the shot (this is quite difficult to do unless you use an alt-azimuth mount with slow motion controls). This can be done regardless of whether you shooting without filter or with filters as you’d just need to remove the filter, align the camera and put back the filter before taking the shot in the later case. The way to do is the analemma is to know or estimate the exact position of the sun at the winter solstice and at the summer solstice at the same UT at your location. This will set the requirement of the maximum focal length you can use (and hence the size of the sun’s disc on the sensor) and how you can emplace the whole set-up with regards to the local features you’d need either to include for reference purposes or for the landscape shot to be overlapped against the analemma.This is just to get started. The nitty-gritty details can be discussed later.Hope it helpsAndrea T.