A Night Time Choir Rehearsal

I recently got the opportunity to photograph a choir rehearsal at Trinity College Chapel. I have visited Trinity College, Cambridge on a number of occasions, it is a short walk from our house, however, I had never visited the chapel. The rehearsal was in the evening, and we were still in winter. It was going to be dark!
I do enjoy the challenges of these types of photography opportunities because they challenge you, your technique, and your equipment. The challenge was made a little more difficult as the choir was being asked to rehearse at the centre of the chapel and not at the far end as would be usual. The final challenge was that I was there as an interloper so I would not be able to set up the shots as I wanted. And what was convenient for the performers was clutter to me so compositions were often compromises.
The Canon 5D Mk4 has an excellent sensor and is fine working at ISOs of 800 and 1600. However, you need to note that high ISO sacrifices resolution when it is cleaned up in post processing. As an aside, I work at ISOs multiples of 50, 100, 200, 400, 800, 1600, etc as I believe the in between options, e.g. 320 are not as effective. I came across this a number of years ago but can't remember where, and a quick Google search is not showing anything. I had my workhorse Tamron SP 24-70mm f/2.8 lens wide open and at a focal length of 24mm to achieve a depth of focus. The shutter speed was around 1/20 sec which handheld I find fine with the Tamron stabilisation. It is always a compromise, which is what makes it fun!
The lack of light, the harshness of the lamps and not being able to get too close for fear of disturbing started me thinking. I had this opportunity and I did not want to waste it. I also had to produce something to show if I wanted to be asked back.