Does one get more detail beyond the minimum focus distance of a macro lens?

Question

I've always wondered what happens when one get's closer than the minimum 1:1 distance of a macro lens. I am choosing between a lens with Internal focusing and the other with an extending barrel.

The 2nd option would obviously reduce my working distance and thus I'm trying to ascertain what, if anything, I'm losing out on.

My subjects are fish, so lighting won't be lost as it'll be above the subject not from the camera.

Tldr; Question: Does one get more detail beyond the 15cm minimum 1:1 distance of say a 105mm lens?

Answer 1

The reason that Maximum Magnification of any lens, including a 1:1 Macro lens, is at the Minimum Focus Distance is because that is as close as you can be to the subject and still be able to bring the subject into focus.

What happens when you get closer than the MFD of any lens? The lens is unable to focus at that distance, because it is closer than the minimum distance that the lens can focus. Your subject will be larger in the frame, but it will also be blurry and out of focus.

What happens when you get further away than the MFD from your subject? When you move further away from the subject the subject will appear smaller in your image. If a lens' maximum magnification is 1:1, it can only achieve this magnification at the MFD. If you move back you will no longer have 1:1 magnification of your subject. The further back you move, the smaller the relative size of the subject in the image. You will also need to refocus on the subject that is now further away from your camera. Since you are further away from your subject, thus rendering the subject smaller in your image, you will lose some detail of your subject.

Answer 2

As Michael Clark wrote: If you go nearer with your macro lens (or any lens), than the minimum focusing distance, you will get an out of focus (= unsharp) image. You would need to add additional equipment to enable your lens, to focus at shorter distances, like either a macro screw-in lens (like a filter, which screws into the filter threats of your lens) or a macro extension tube, which goews between your camera body and your macro lens. Both devices will give you a shorter minimum focusing distance. - with the macro lens the quality will be slightly degraded (one more optical component in the path of light), but the lens parameters will be retained - with extension tubes the image quality will be retained, but you "loose" some light, the image gets darker and you need a longer shutter time or more light