I´ll guess the minimum exposure time to avoid star trails is linked to focal length?
Impressive. Have never tried myself. It doesn't look easy at all. The results are worth the work whatever it may be.
Thanks for sharing it!
Maximum for 20mm would be 20 seconds, there's still a tiny amount of observable tracing. Usually 15 seconds gives the best results.
Winder lenses such as the popular Samyang 14mm F2.8 can do 30 seconds, but you'd still see trailing. 25 seconds is my suggestion.
It's usually cheaper to invest in a small star tracker and couple it with a moderately wide lens, such as a 24 or 35mm at F2 or 2.8 than to just buy a fast wide angle that likely has some pretty annoying coma wide open.
Do you have a link to something like "making star images for dummies"?
I am interesting in learning a bit about the technique without having equipment that can trace the stars (I assume that the images you show are shot just with a steady setup?).
You talk about stacked images. I want to learn how images are stacked and how you prevent that the stars "moves" when using a steady setup.
It is difficult to stop rotation of earth just for a short moment? :-)
I don't really have a link where I learned my techniques from, it's mostly self-taught and studying online photos. My setup is very steady, heavy duty RRS tripod and a big ballhead, heavy but it's required. The images up until now were shot in the Southern Highlands of NSW, it gets really windy at night, there's actually some shake if you look very closely. It's better to hold the tripod down. I do carry 1L of hot water during these trips (Winter here), so my hiking bag actually makes a decent counter-weight.
Exposure time is a matter of focal length. 20mm here, so about 20 seconds would be pushing it. I usually do 15 seconds. By the 500 or 600 rule, it can be longer but that rule is a very flawed basis for exposure time.
12mm 30s
14mm 25s
20mm 15-20s
24mmm 15s
35mm ~5-8s
Above: Use a tracker
For stacking, I didn't use focus stacking. I'm talking about image stacking to reduce noise. The photos were shot at ISO3200 or 6400, however you can see the sky looks clean, looks like an ISO400 or lower shot. That's because I blended multiple exposures and stacked them to reduce noise. The process is simple in photoshop:
- Files > scripts > load files into stack > attempt to align
- Check result, good? Convert to smart object. Bad? Align manually
- Layers > smart objects > stacking mode > median
Doing so also removes any trailing left by planes and lucky meteorites/shootings stars that you caught. Planes aren't a problem now due to the virus. For the meteors, I just paint them in using masks.
Sometimes using a mask to remove the foreground helps with automatic alignment. If photoshop is mean, just zoom in like 400% and do it manually, it's not too bad.
Sometimes focus stacking will be required if the foreground is too soft despite the lens being at infinity.
Here's a good channel:
https://www.youtube.com/channel/UC-KNiVo4X76cJIMphH1lEdAHere's some more information on exposure stacking:
https://www.youtube.com/watch?v=Rydg7JGTAbw&t=183s It's more complicated if you want to do panoramas and/or stack the foreground to reduce noise as well. I just ordered some parts to make a panorama setup so I can do better vertical stitches.
I'll post a photo of my equipment later today.
