New to portrait photography and having trouble getting crisp images in low light. Shooting on a Rebel T5i with the 18-55mm kit lens. AF and stabilier on. Is there something I'm missing or is it time for an upgrade to something with a better sensor or ISO?
f/5, 1/100, ISO-3200
"...how much light is more light?"
That is the question, isn't it. And, there is no specific or hard fact answer. It all depends on the unique conditions. That is why nobody here can tell you any specific settings or exactly how much light you need. Even how fast a lens you need without actually being there.
I can tell you outdoors in full Sun is way brighter than almost any indoor places. Except an operating room perhaps. Your eye adapts to what available light there is and does a pretty good job at it. A camera can not do that. It is a fixed device that needs to know exactly how much light is present.
"Not a sunny day, but still plenty of natural light."
This is great and the best light there is.
"...four bright recessed lights above them"
Most likely a non factor. They would have to be very to extremely bright. But then given again enough of them they can help.
"Even my outdoor shots on cloudy days seem grainy."
My most favorite shooting condition is a cloudy day. Diffused sunlight is absolutely the best. In your case of grainy photos on a cloudy day is a settings issue. You are most likely using too high of ISO when it is not needed and not the preferred way of adding light. Of course that doesn't mean shooting right before a thunderstorm cloudy day!
You did notice what I did to your sample photograph? That was two simple clicks in Photoshop. Using your settings, PS can correct it to a large degree. Right? Now, if you had used Raw format the adjustment is far greater and a lot more can be done.
The one thing you can do right now to improve your photos, any of your photos, is to use Raw format and a post editor. You get a very good one free from Canon. It is DPP4. I prefer Photoshop. It can be as easy to use or as deep as you want depending on how much learning time you are willing to apply. Two simple clicks to 20 to 200, all what you want in the end.
So meter carefully. Focus carefully. Watch that ISO so it doesn't go too high. If you had auto ISO turned on, turn it off and set it where you want it. And, use Raw format instead of jpg.
"you might also have an issue with mixed lighting throwing the white balance/flicker detection off."
When you use Raw format, white balance (WB) is not an issue or factor. The main most important thing is exposure, correct ISO, and focus with exposure being the less important. Out of focus (OFF) is nearly impossible to impossible to fix in post editing.
"Yes it is, mixed lighting is an issue with RAW..."
Well the fact is Raw is better then jpg at handling WB and that is the point. Raw will handle WB corrections way better and is the format of choice. Not that I think your reasoning is valid in the first place though.
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