Setup for macro photos of flat surface with macro lens and led ring

Question

I need to take photographs of a close flat surface with controlled lighting. I have an idea to do this, which is to use a dslr with a macro lens. Use a LED ring (which I see are usually used for macro) and a tube extending !

The custom cylinder to block light will be some 3d printed cylinder to go over the led ring. I can make this between a few centimeters to about 10 centimeters.

What type of lens would be best for this close work. I have macro attachments to my canon dslr, but it was wondering if there is a better lens that can focus in this short distance.

To make this more generalized. I am curious about focusing on a flat surface close to the lens. For example, if the camera is taking a photograph of a printed photo. Or if I wanted to photograph a wooden table to see the grain and fine details.

Answer 1

You'll need a lens with a minimum focus distance small enough to accommodate your rig. (See also How close can a lens focus?)

There are several ways to accomplish this. Your secondary macro lens, which mounts on the front of the existing lens, is one way to accomplish this, but won't necessarily be sufficient and certainly won't give the best image quality. So, you can find a dedicated macro lens (probably a wide-angle one, as these will have a closer working distance as a general rule), or you can go for an alternative technique like reversing rings or extension tubes, in which case see How do I calculate what the working distance will be with a macro reversed lens setup? and How do extension tubes affect focusing distance?

Because your setup implies a very close working distance, you may have trouble finding a lens that works — even a designated macro lens. Most macro lenses in the 50-60mm range have a minimum focus distance of around 0.2 meters, give or take. (This is measured from the sensor, not the front of the lens.) Longer focal lengths will be even longer, and 35mm macro lenses (like the Pentax DA Limited 35mm f2/8 macro) — often used for document reproduction for just this reason — can usually focus even closer.

But that might not be close enough for your particular use. For this reason, one of the alternative setups is probably your best bet. You might also want to consider a non-DSLR. Many small-sensor compact cameras have a very, very close minimum focus distance and a built-in macro mode.