extension ring for my SUBAL FS2

I ve just received my Nikon 12 24 zoom, and I m not sure that the extension ring SUBAL EXR40 is the good one for the zoom with the DPFE2 dome ,

Works great wtih the 18 35 but seems to be too big with the 12 24

Which one do you use ?

I use the EXR 50 even, but thats mostly because I used to use a diopter. Ive seen others use EXR20. I really dont think it matters much. This is on a D100 btw.

I recently did a comparison test with and without diopter and definately dont use a diopter. Subal seems to agree on this.

Cor

Thanks for the answer Cor, Ill use my EXR 28 , what about the minimal focusing distance without diopter ?

With the D100 the correct X ring is the 50 mm. See the port chart at Subal. Any other ring will not put the image at the correct nodal point on the lens. You will get a degraded image if you do this.

What does degraded mean? I recently tested images made with an EXR 50 and an EXR 20, and they looked pretty much the same to me. I unfortunately dont have the images nor the EXR20 anymore

Cor

Look in the corners. A high res. image or a large print will show distortion in the corners. You may see some chromatic aberrations as well. Also look at the sharpness of a close-up of fine detail. You will see some softness if you compare images with different X rings. Compare images with the aperture opened up.