Interesting conversation with a customer today. She's a professional photographer. She's hired a Sigma 35mm Art lens from us, for some group portrait work. She's just taken delivery of it but is having problems, so she called us to ask for advice. Me: So what kind of problems? Her: All my pictures are coming out really much darker than I expected. Me: OK. What camera are you using? Her: A Nikon D850. Me: Great, that's about the best camera there is. Let's look at how you're using it. How are you setting up the camera to take these shots? Her: Well, I'm setting the aperture to f/5.6, because I want enough depth of field to get everybody's face in focus... Me: OK, sounds good. Her: ... and I've set the shutter speed to 1/250th, because there will be some babies in the groups, and I don't want their movements to be blurred ... Me: OK, good idea. Her ... and I've set the ISO to 2000, so I don't get too much noise in the images. Me: OK, that makes sense. Are you using studio lights or flash? Her: No. Me: ......... No? Her: No. Me: I think I can see the problem here.