So I own a Minolta XD7 (XD11 for American users) and few months ago I had the opportunity to by a Sigma 400mm f8 mirror lens in MD mount but how do you use this correctly on a XD7?? There is no diaphragm in this lens thus no extra lug to let the camera know there is one. So i'm guessing the camera just measuring the incoming light and does not take any account of the missing diaphragm? Do I have to use Automode, Aperture Priority Mode or Manual Mode? I dry fired it on a XG2 and installed a 35mm lens who gave me 1/60 sec on f8 and so did the 400mm when it looked trough it so the XG2 just measures the incoming light I guess but what about the XD7? I bought this lens new in box for about 10 euro from a sale-out of a photo shop so it's a great deal anyhow.