I have a picture frame that is 2 1/2 x 3 1/2 inches. I would like to know what kind of dimensions, in pixels, I should use with my Nikon D3300 to make a photo for the frame?
It's easy: you take the desired DPI (dots per inch) and multiply it with the frame size. Say, your photolab (or printer) prints with 300 dpi. Then your picture must be at least 2.5*300 x 3.5*300 = 750x1050 pixels. However I doubt that you have such a low resolution in your Nikon :)
I recommend to take photos with maximal available resolution. So you will have more flexibility for cropping them and you can always resize them (though it's not necessary - the photolab will do it).
There are three basic principles here:
- You want at least 200 pixels per inch in your print. For most subjects, most people will start to see pixelated blockiness if you have less than that. 300 pixels per inch would be better, and that's especially true for a small print like this, because people are more likely to examine it very closely. For large prints viewed from across the room, 100 ppi may be sufficient. (See Is there a general formula for image size vs. print size? for more.)
- More pixels never hurt. If you figure out that you have 2000 pixels per inch when all you need is that 300, no problem.
- The shape of a print is called its aspect ratio. You need to make sure your image is cropped to that shape beforehand, or else the printer will cut off the edges in a way you might not have expected.
So, working backwards... the aspect ratio you're looking for is 2½ by 3½, which is 2.5:3.5, or in whole numbers, 5:7. This is a traditional shape for prints, but is not common out-of-the-camera in the digital world, where most cameras are in either 2:3 or 3:4 format. Your Nikon D3300 produces 24-megapixel images 4000 pixels the short way and 6000 the long way, so, 4000:6000, or 2:3.
To get to a 5:7 aspect ratio, you'll need to crop. 4000:5600 fits 5:7, so you'll need to take 400 pixels from the long direction. The easiest way is to just take 200 from the top and bottom, but you can do it however.
In doing this, you'll have 4000 pixels along the 2½" side, and 5600 along the 3½" side. With a little division, we see that this works out to 1600 pixels per inch — which is way more than needed for #1, but as you can see from #2, that's fine.
You could also crop a smaller portion from the image — just make sure your rectangle is in the 5:7 proportion. If we pick 300 ppi as your minimum, that means as long as you're at 1050×750 (that's 300 times 3.5 the long way and 300 times 2.5 the short way) or larger, you should be fine. That means that if you want, you could choose just a small detail from your image.
Do be aware that cropping less and printing smaller has an advantage: it will hide lens defects and other artifacts, and even technical errors. A 4000x6000 image might look out of focus printed at poster size and inspected closely, but perfectly sharp at 2½ × 3½.
Avoiding calculations can be done with image editing software. If you take software such as Photoshop Elements and select the cropping tool, you will see some number entry boxes along the menu bar at the top of the image frame. Enter the dimensions you want in the width and height boxes and 300 in the pixels per inch box. Crop the image using the crop tool, which will make every crop the size you have specified.
Alternatively, you can enter the dimensions in such a manner that the crop box will always be the maximum size that can encompass your image. All image editing software should permit the first method of cropping your image and then you save the file. It will usually default to .jpg as the file type but as long as you save the file only once, this should not be an issue.
As you are new to photography, it may be worth buying a book on image editing for beginners. Look for Photoshop Elements or if you are on a Macintosh, look for the same beginner's book for Pixelmator. Remember that you cannot damage anything by experimenting. Make a copy of the file you want to work on and include copy in the name. That way you will never be working on important original files. If you happen to damage a copy file, make a new one and work with that. Photography is a very practical 'hands on' interest and you will acquire far more knowledge by doing it yourself rather than reading about it. Possibly you could find a local group that shares your interest too.
Finally, treat yourself to a book of images which you like (by a photographer whom you admire) and page by page see if you can work out how they created any particular image and when you think you have understood what they did, try to create a similar image. This will assist you to gain skills very quickly.
Hope this helps. Enjoy your image creation. :)))