One of the trickier aspects of using a camera with macro lens is when the copying camera is not the same size as the film original...36mm x 24mm slide being copied by (for example)
- a T6 with 22.3mm x 14.9mm sensor...you need to find a lens with FL and and extension tube which is 0.62X FL in length in order to copy the image at 0.62X
- A 7DII with 22.4 x 15.0 mm sensor...you need to find a lens with FL and and extension tube which is 0.62X FL in length in order to copy the image at 0.625X
...62mm of extension tube with lens which is 100mm FL, yet tubes most commonly come in 12mm, 20mm and 36mm lengths
Yes, you can use 68mm of tubes and that results in 0.68X...you lose edges of the original slide.