Jason Brunner has a great video on Youtube illustrating the proper knocking routine. My memory is you knock first on the side of the bottom like against the edge of a sink, and then knock a few times right on the corner before setting it straight down.
Since I'm usually developing film after midnight and until about 3 AM, I like the heavy rapping. It keeps my neighbors wondering
I love the wilderness and I love my trail cameras, all Fuji's! :) GA645, GW690 III, and the X100 which I think is the best trail camera ever invented (to date).
I find I tap too hard, but it's due to frustration from having 3 rolls come out with bubbles. Considering that until the first roll happened (1 1/2 years ago) this had NEVER happened before and I'd never made any sort of special tapping effort, I was baffled. Especially when it happened twice more. I do worry about cracking the tank though so I should probably pull back a bit.
This is a bloody good question. It is all down to where you are. I have never had problems in the UK but have severe problems in Kabul. see this thread for solutions to drying marks (another problem in Kabul) as it also helps on air bubbles too. FWIW, although I can dislodge some air bubbles by banging th base of the dev tank on a hard floor, I cannot remove them all. Adding a tiny amount of wetting agent to the dev seems to help a lot.
How do we know without opening the tank to look? Maybe an experiment with outdated or sacrificial film would be in order. I use such vigorous agitation that there sholud either be no bubbles or bubbles everywhere, But I still give it a good rap when I set the tank down.
This is very good advice
Sacrifice a film - it pays dividends in the long run.
I not only "drop" my tank (somewhere between half and once inch) but I also give it a generous (vigorous) rotating wiggle too
It is most critical at the initial fill, when the air can stick to dry film and/or reel.
At subsequent agitations the tapping and wiggling can be reduced
Its amazing down tenacious air bubbles can be.
It’s something of a Catch22 situation – you need enough spare room in your development tank to allow thorough turbulation (hence mixing) of the developer, without excessively aerating the developer
Some films/developers/water types are more likely to aerate than others – so its worth checking how your combination behaves.