I am a PI who uses my 60D for surveillance. Occasionally, we use another person, who is a professional photographer, to do some nighttime surveillance for us because her system is capable of capturing great shots in low light. I've asked her what she uses and realize the equipment is what offers the capture of nighttime photos. She uses a Nikon and a Sony (unsure of model) with a zoom Nikon 1.8 lens. I recall her saying the camera is capable of 24,000 ISO but I attribute the lens as the main reason for better night shots. Anyway, I would like to achieve the same with my camera, though, after continuous playing around, I don't think it's capable along with the lenses I have which are the EF 100-400 (great for my daytime shots), the EFS 50-250 cheapy (came with camera) and the EFS 18-135. Playing around with ISO and white balance, I can achieve some decent shots in lower light but nowhere near what the photographer can do and obviously, I can't use flash. Therefore, I'm seeking advice/suggestions of how I can get those better nighttime shots, which I know will involve spending some money for a better lens and/or camera.
Thank you for any help you can give.