I have the elements for a Symmar-S 360mm, 6.8 lens. Beautiful. Recently have been looking for a Copal 3 shutter so I can use them with my 8x10. The shutters are so expensive. So, I bought a Symmar-S 300, MC in a Copal 3 tonight,($330) thinking I can use the 300 with my 4x5, and switch over to the 360 6.8, for use with my 8x10. What is the best way to judge the aperture difference. Will 5.6, wide open for the 300, be 6.8, wide open on the 360? I thank you in advance for information on this. Robert