Howdy! Has anyone had any success using longer exposures like 5 seconds x 1200 seconds? Or longer? I'm going after the Lagoon Nebula tonight. Need some advice!
Seawild, yes Lagoon can be imaged with AS. In AS, the bulk of photo averaging takes place with longer exposures of anything more than 1sec. At one second or less, minimal averaging takes place as every exposure is aligned and stacked. The longer the exposure setting (2 sec or more), the more averaging takes place. Averaging is what removes noise from the image... small bits of sensor noise that appears in one image, will be cancelled out by the next image, because sensor noise changes randomly from one image to the next. With an image of the dark sky, the sensor is working very hard, while being photon starved, so noise can be a huge distraction. Photo averaging cleans up all or most of that noise. But in AS, the bulk of averaging takes place with multi-second exposures.
As an additional benefit, AS brightens multi-second exposures. There is a significant, although incremental image brightness increase as you move the exposure slider from 1 to 100 seconds. This was done to simulate a single long exposure such as can be taken with an Android phone or DSLR. I typically use exposures of 1 to 10 sec with ISO's as high as 16000 on my iPhone 15.
Exposures of 1sec or less, are not averaged before being aligned and stacked. So why would I ever use an exposure of 1 sec or less? I actually use 1 sec exposures regularly, because of wind gusts at my observing location. Exposures of 1 sec or less are ALL aligned and stacked. With an exposure of 10 seconds, you rely on your mount's tracking to keep the images aligned while averaging is taking place. A gust of wind on a 8" Newt can ruin the 10 sec exposure. But if every short exposure is aligned and stacked, there is a much higher chance of completing a useable image.
I'd suggest starting with exposure set to 10 sec with number of exposures set to 10, just to see how the image comes out. If the noise level in that final image is OK, increase the number of exposures to 50, 60 or even 150... however long you are willing to give the camera to define resolution. If the image is too noisy, increase the exposure time to 12, 15 or even 20 sec. Do not hesitate to use high ISO settings... even your maximum ISO. You will not need a filter for the Lagoon because iPhones do not have an IR blocking filter built in. When you've taken an image of M8 that meets your standards, move up to M-20, Triffid. It is quite bright too.
There is a photo of M8 in my gallery "Phonetography" album, but it is severely vignetted because of the zoom eyepiece I was using to take the photo. It was taken in 2022 using NightCap, before I switched to AstroShader. But that image will show about what you can expect with just 15 seconds of averaging 1 sec exposures: https://www.cloudyni...59-geezergazer/
I look forward to seeing your images here. Good luck and Clear Skies.
Ray