How to take photos of my artwork for printing reproduction? I have a Canon EOS 700D and cannot seem to get them 'straight'; they always seem askew?
Make sure you are taking the photo exactly straight on with the optical center of the camera aligned to the center of the artwork. Imaging a line passing perpendicular to the camera sensor going through the center of the lens and it should reach the center of your artwork.
To make this easier, place the camera on the tripod with a multi-axis level and adjust until it is level in tilt and pitch. Then place your artwork on a support and adjust it until it lines up as described above. It should take care of any skew but not distortion.
To avoid distortion, the only thing to do is get a distortion-free lens. Most macro lenses are designed to that goal but that does not mean they manage. Check out technical reviews of lenses to see how they perform in terms of distortion. For zoom lenses, distortion almost always varies with focal-length, so be sure to set the focal-length which minimizes distortion. These tend to be on the expensive side, so if you are doing this only from time to time, consider renting.
Use a longer prime lens. The 50mm f1.8 comes to mind (it is a short tele for a crop camera, such ad the 700D). Canon lens don't come any cheaper, and this one has hardly any barrel distortion (design of normal prime lens has been mastered long ago, so they can be made both good and cheap).
Align your artwork with the plane of sensor as closely as possible.
Avoid wide angles if you can; they magnify any errors in alignment.
Use a sturdy tripod and a wire release; then you don't need to worry about exposure times (your artwork is not going anywhere). Avoid flash if you can.
The optical center of the lens must also be perpendicular to the plane occupied by the 2D artwork.
Simple to achieve with a small mirror placed flat on the artwork. Only when you see your lens reflected 'dead-center' in the camera viewfinder (SLR type) will the lens be perpendicular to the artwork.
Making a faithful photographic copy of works of art is a daunting task. You will likely never make a faithful image but you can get close. All cameras suffer from an optical distortion of “magnification”. You are likely working in too close. Things close to the camera reproduce large and the things far from the camera reproduce small. The corners of the art work you are imaging are more distant than the center. This distance difference induces a distortion. You can mitigate by backing up and imaging from afar. Try setting the zoom at about the middle of its range and adjusting your camera-to-subject distance to fill the frame.
All camera lenses suffer from “barrel” distortion, observed as a bulging out of the sides of a square objects or “pincushion: distortion, a bulging inward. These distortions battle our desire maintain the “squareness” of art work.
The only way to mitigate is to set the camera square on and step back. Advanced editing software can also alleviate this plague
If you are willing to fix this on post production, use a software like Lightroom which have lens correction profiles for the given camera and lens. This will remove chromatic aberration, and distortion on the first hand.
Than you can apply perspective correction, if your photograph have minor perspective errors you can successfully restore it. There is auto perspective correction as well, if your artwork have straight frame, it can use it as guides. Or you can do it manually.