Originally posted by tezza Yes thanks jatrax I will try that;but I do not know or can see these contacts on the lens, but it is quite a few years old & one of the cheapest to boot so..... see how I go
Look at the lens mount, you should see a series of small metal balls sticking up through the plate. These are spring loaded and make contact with the contacts on the camera plate. The number will vary from 1 to 6.
However, if you have no (zero) contacts then you have an older all manual lens. In this case the camera must be in the 'M' manual mode and you need to use "green button" stop down metering.
Please post a picture of the lens mount without glare and we can tell you quickly what you have. Also post the exact name and description of the lens or a picture so we can tell what model you have. Sigma has made a number of 70-300 lenses over the years so that is not enough to tell which one.