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I also own a D90 and the only reason to upgrade is to a Nikon FX camera, which is extremely expensive (but worth it) and it requires all new lenses. My suggestion is that when you're ready to upgrade, upgrade to an FX camera.
Sorry, there was a problem. Please try again later.I've used Sigma lenses, they work just fine. the camera body is less important than the lenses. If you feel that newer bodies have more features that you would like (faster burst, Wi-Fi, etc) than sure, upgrade; but keep in mind that picture quality won't improve much (if at all) if you are using good lenses!
Sorry, there was a problem. Please try again later.The D90 is a great camera. A nice upgrade from the D90 would be the D7100. If you wanted to go full frame, you should look into the D610. Sigma lenses will work with both cameras. Of course, you cannot bead the optics in NIKKOR brand lenses, so Nikon recommends using NIKKOR brand lenses.
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