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Ok, so for those that are interested, here are the results of my ISO exposure test on the f/5.
I ran the ISO at 800 for all subs and took 20 of each
At 22s, 20s and 18s the sky glow was too high but interestingly the star count in DSS didn't change.
At 16s the sky glow became almost acceptable and the star count dropped by about 10%
Finally at 14s the sky glow was acceptable but the star count had now dropped by a huge 50% !
It would seem that there's a cliff that the image drops off at a certain point.
Interesting.....
Am I right in saying that an f/5 gathers light 4x as fast as the f/10 ? So in theory a 15s sub would be roughly the same as a 60s sub on the f/10 ?
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