The curved glass distorts the fish. You need flat sides or at least 1 flat side to get a good picture. Buy some acrylic sheet, get the glue and make your own rectangular "picture" tank? Maybe buy a small 5 gallon aquarium? Find one on Craigslist or FB Marketplace?
A way to calm the fish is to use clove oil.
Example:
https://www.walmart.com/browse/heal...SsLH3dOTccaArcNEALw_wcB&gclsrc=aw.dsSince you can get a bunch of minnows, experiment. 1 minnow of "x: length, one drop, 2 drops, 3 drops, etc? You want to slow the fish down and not knock it out completely for the fins to be sticking out and visible. Don't use a flash - you might get a reflection from the "glass" or freak out the fish.
Or spend more $$ and get this:
https://www.amazon.com/SureLife-Tranquil-Fish-Calmer/dp/B07VFXYSC45-8 drops in about 3 gallons of water will calm down a half 5 gallon bucket full of fish when added to the water......... It might take them a while to calm down though. Adding more will flat knock them out. I haven't left them in there long enough to kill them, as soon as they stop flopping around I take the lid off the bucket and weigh them, then dump them into the pond.
One customer thought I was stocking dead fish (they WERE belly up). I told him that I had to stock his neighbors pond with fish, and if the fish were still "dead" when I came back in 20 minutes I'd refund his money AND bring his fish order at no charge the following week. We came back and he asked me about half a dozen times where his dead fish went. LOL