How to shoot in RAW format on Nikon d5100?
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Please don't say look at your manual, because I lost it: c
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Since you don't have the Owners Manual just follow these steps.
Step 1 - Google the information for the Owners Manual such as typing in Nikon D5100 Owners Manual
Step 2 - Click on the Link for the Nikon D5100 Owners Manual
Step 3 - Find the Page on how to change the Image Format to Raw
Step 4 - Follow the Steps of the Owners Manual
Look at Page 47 of the Owners Manual
http://www.nikonusa.com/...oprint.pdf
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You can download a copy free from Nikon (you'll need a pdf reader if you don't already have one, but Adobe, Foxit and Sumatra are also free to download) - and reading it should ALWAYS be your first option.
I'd imagine there's an option in the menu where you set your resolution.
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Once you download the user manual, look on page 48