I am looking at at Caltar 75mm 4.5. The lens is mounted in a copal press shutter with 6.8-45 aperature scale listed on it. Am I getting something wrong? Although the lens is a 4.5 the shutter only opens to 6.8--so, the max aperature I will be able to use is 6.8. I hope this question makes sense--the seller is very confused and now so am I.