Ever since sunday the night sky has been overly cloudy, so when the skies finally cleared yesterday night, I quickly took the opportunity to try the Slow Shutter Cam app. This app takes 15 pictures per second with the standard iphone shutter speed of 1/15 sec and then stacks them together to artificially create a shutter time of multiple seconds. Although this seemed usefull at first, the resulting photos have very bad signal-to-noise ratio’s as is evident from the pictures below.
The app doesn’t seem to cope very well with noise from the CMOS chip, which is mostly red. The red noise is in fact so bad that the red channel shows nothing but noise. The image I uploaded in the previous post was a stack I made myself from 13 1/15 sec photos taken with apple’s camera app. This image was of substantially better quality than the Slow Shutter Cam result, indicating that I should probably stick with apple’s camera app. The picture below is an 8 second exposure photo taken with Slow Shutter Cam. The smeared out stars are due to earth movement and emphasize the usefulness of an RA-axis motor to follow the stars while the shutter is open.
Next time the night sky shows itself I will take a lot (about a 100 or so) of 1/15 sec photo’s with the standard camera app. This would also allow for manual adjustment of the telescope during the series to keep the deep sky object focussed. In addition, I will use my new light pollution filter that filters out unwanted wavelengths including those emitted by mercury and sodium street lights.