I went outside last night and made some... pictures.
The details about my setup:
- Sony alpha 6000
- Varexon 2.8/135mm lens (would be 202.5mm on 36mm film)
- ISO 25600
- 3 seconds (a bit too long, given the Rule of 500)
- stacking of about 10 images with
Given that I was able to record 10.20 mag stars with the same lens and a single 2 s and ISO AUTO (= 5000 in that case) exposure - these faint stars appear as pale blue specks, I expected much better results with a higher ISO value. But no. They seem to be washed out.
Merak (beta Ursa Majoris), the Surfboard Galaxy and the Owl Nebula:
I've seen tips to use the highest ISO when doing astrophotography, but it seems detrimental. What are some useful hints to find the right ISO value?