The problem when shooting through glass or Plexiglas as in photographing at an aquarium or through an airplane or other window is that you can often have problems with reflections. Pressing your lens hood against the glass can help somewhat but, restricts your angle of view and in an airplane, the vibrations can be transmitted from the window to the camera.
I solved the aquarium type of problem by using a one-dollar black plastic salad bowl with a round hole cut in the bottom. Pressing the bowl against the glass and sticking the lens through the hole will provide a shot without most reflections. The downside of this technique is that the salad bowl is large and unhandy and absolutely useless for travel.
I have solved the problem with a collapsible black dog bowl with lens hole cut on the bottom of the bowl. Most of my Sony lenses that I will use for this type of shooting have maximum diameters of 67mm, so I cut a hole that size in the center of the bowl bottom using an Xacto knife.
The bowl works great to eliminate reflections and it is a very handy size and weight for traveling anywhere. It weighs less than two ounces, costs $2.80 USD and folds down for easy carrying. The carbinier clip makes it easy to carry and easy to hold while shooting. I now have one permanently in my camera bag and one in my photo vest. The bowls come in sets of two from Amazon.com...
https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1