Hello,
I'm a total beginner and I need help figuring out whether what I planned would actually work.
I have a smart phone with a tripod and a clip-on telephoto lens. Smartphone is pretty decent at taking long exposure frames which I then stack to obtain my images.
I'm going to try adding telephoto lens (that magnifies by a factor of approximately 7) to photograph specific smaller parts of the sky, instead of multiple constellations that otherwise fit into my camera's FOV. I also hope that lenses large front aperture (much larger than my phone's aperture) would allow me to capture more light.
However the part that's bothering me are the star trails. Without the lens, my phone can take 20 second exposures with negligible trails - this corresponds to the formula 500/(crop factor * focal length). However once I add the lens, my effective focal length will increase by a factor of 7 meaning I'll have to cut my exposure to only a few seconds.
That can be addressed by taking way more photos, except the drawback is vastly increased memory use.
But I was wondering whether the large lens aperture will make stars appear brighter thereby reducing this problem? Stars are point sources and appear only as Airy discs on photographs anyways, so a larger aperture should make them brighter?
Edited by Dominoes3442, 13 May 2025 - 07:26 AM.
