With a reversed lens, normal body-to-lens aperture control is often lost unless you use a special adapter.

For Nikon F-mount lenses with mechanical aperture linkage, a device such as the Nikon BR-6 auto diaphragm ring can provide aperture control when the lens is reversed. A simpler DIY option is to hold the lens’s aperture control lever in the position you want.

For Canon EF lenses, aperture control is electronic, so you typically need an automatic reverse macro adapter that maintains electronic communication. A common workaround is to mount the lens normally, set the desired aperture, then remove the lens while holding the depth-of-field preview button so the lens stays at that aperture.

So yes, it is possible, but the solution depends on your lens mount:

• mechanical-aperture lenses: use a reverse ring with aperture control or set the lever manually
• electronic-only lenses: use an electronic reverse adapter or the DOF-preview trick

If you plan to do this often, a dedicated automatic reverse adapter is the easiest option.