Verified answer

You can easily make them with that camera. You have plenty of resoilution. A poster may...just MAY be a tad soft up close, but from a normal viewing position you're good to go.

Yup! I have a D90 it works great for poster sized images. I have no problem with it at all. The D90 has great ISO settings, but remember to always shoot with it as low as the light requires- because that will make it more grainy.

12.3 MP will be fine for large format prints up to 30x40 inches. Also, check with your print shop to make sure they print at the same resolution you save your photos (I usually use 300dpi). Good luck!