What Calculator website? Do you have a link? 1/2 stop would probably work for the 150 but I'm not so sure about the 60mm, you might need a little more. If you have a metered prism you shouldn't have to worry too much, the TTL metering will give you a correct reading. Now, if you are using studio flash for lighting you will need to make an adjustment. As the old saying goes, "Test before photographing anything important" In situations (testing exposure) like this, a polaroid back can be useful.