[stevebrot]

Modern sharp designs shot with nearly open aperture are very tricky.

You are correct that infinity might not give the sharpest results, though there is no need to shoot at wide aperture or at high ISO. The bright spot is very bright and one can get away with modest ISO (say 400) and f/11 easily. I did not shoot fireworks this year, but the last time I did, it was ISO 400, f/11, 5s and 21mm on my K-3 using a wired remote. They were going to be being launched from a barge off shore about 100m and before it got too dark, I used manual focus in live view put focus on the barge and taped the focus ring. When they actually started the show, I adjusted the ballhead to the right point in the sky and triggered exposure when I saw the rockets approaching the "burst zone". That actual point of explosion was likely further away than my set point of focus, but the burst spread would have placed much of the action nearer as well. Hyperfocal at f/8 is at about 3m so I easily could have gone ISO 200 at f/8 and gotten sharp results. I also did some shots at ISO 800 and f/16 and was pleased to see that the results were practically noise free.


Steve

(...of course 100m and infinity are only a degree or so different on the focus ring...)

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Last edited by stevebrot; 07-06-2018 at 06:17 PM.

[CNunez]

I always stop down to about f8, then set the focus to where it goes hyperfocal. ISO 100 and usually around 2-3 second exposures. Seems to work well. (this is a rough guestimation of what I normally do) I never set the lens to infinity. It's easier to just use the hyperfocal scale.

[richandfleur]

Even with some wide angles fireworks may be too close to the camera for infinity focusing to produce best results. Modern sharp designs shot with nearly open aperture are very tricky. Thus, always manually focus at known distance where the fireworks are beforehand and you are set. This means magnified liveview. OVF is not enough.

Yes a wide aperture is great for low light, but produces just a narrow band of the scene in focus, especially at close range.

Live view, with digital zoom and focus peaking is ideal for manual focus work such as this. Actually this is another of those times where mirrorless is as good as a DSLR, given you're running the DSLR in 'mirrorless mode' anyway.

Again though, can the OP confirm they had Pentax sensor SR stabilisation turned off whilst mounted on a tripod?
If not, this could account for the blur when every other aspect should have produced a good sharp shot.