The sun set tonight at 4:20 PM. That's pretty early and I felt like some sort of ceremonial observance was in order. There was a lot going on really, and some of it got away from me just a bit. Not a problem though, and I'll explain...
I thought we should head down to the golf course and walk along the shore. Look for a couple of boulders at the same time for 
There's a decent size boulder for you. The lens is only mediocre but still fun to play with. A little while had passed since 420 and it was getting darker. Harder to focus, but that's not all. I insist on doing everything on full manual with my Olympus EM5 Mkii. Sometimes that means you have to think about stuff. There can be "higher math" involved.
Anyway, no big deal, it's just that I wasn't thinking and I lost a couple of great shots. My ISO was set way too high (1600) and my shutter speed was way too high (1/800 second)
So here's the thing - and this will only be of interest to camera nerds:
My shots at ISO 1600 suck because they're too noisy. But why shoot at 1/800 second? I can easily hand-hold the Olympus at 1/3rd second! Ok, we don't need to go that slow, but how about something sane like 1/100th second? Watch what happens now with the math. (Understand first that a change of plus or minus "one stop" of light means a doubling or a halving of the amount of light.)
Reducing shutter speed from 1/800 to 1/400 gains us one stop of light.
Reduce further to 1/200th. That's another stop.
Reduce further to 1/100th. That's 3 full stops of light gained by slowing down the shutter speed. We doubled the light three times.
2 x 2 x 2 = 8 times as much light.
That means we can now give back some ISO to match.
Reduce from 1600 down to 800 ISO - that loses us one stop of light.
800 down to 400 - that's another stop.
400 down to 200 that's three stops of light lost, cancelling out the three stops we gained with the shutter speed. Our exposure is exactly the same, except look where we are now - 200 ISO is the base on this camera... essentially no noise.
Higher math. Just need to divide or multiply by two, but that was beyond me. Did I mention the sun set tonight at 420 exactly? What are you gonna do?
Here's one of the shots I lost - out of focus and way too noisy from that high ISO setting. You couldn't print this image at all but If I'd done it right it might have been awesome...
Blah, blah, blah... what are you talking about and what does it matter?
The first shot in this series (ISO 200) is absolutely clean and you could blow it up quite large. The final shot is very grainy and noisy - you shoud see it on a large screen, it could never be printed. Three clicks of my shutter speed dial would have made the final shot as clean as the first. That's math and that's science! :)