Hi, i have recieved an old 100-300mm 1:5.6-6.7 "macro focusing" zoom lens. it is compatible with my nikonD7000, but i have a mysteryous problem- i couldn't find a focus ring on it. -is there a focus ring and it is just stucked? or maybe the lens is only AF with old cameras and there is no manual focus option? thank you, Ariel

SOURCE: trouble focusing with sigma 70-300 DL macro super lens

It will not focus on anything closer than 5 feet.

(From Sigma lens literature) Capable of macro photography, this lens has a 1:2 maximum close-up magnification at the 300 mm focal length. It's the ideal high performance lens for portraits, sports photography, nature photography, and other types of photography that frequently use the telephoto range. It also has a switch for changeover to macro photography at focal lengths between 200mm and 300mm with a maximum close-up magnification from 1:2.9 to 1:2. The minimum focusing distance is 1.5m / 59 in. at all zoom settings.

SOURCE: vivitar 75-300mm lens

The Vivitar brand has been bought and sold quite a few times in the past 10 years.

KEH Camera has quite a few used Vivitar lenses listed on their website. They are priced very low, from just $4 to $49, so it's highly unlikely that the lens is worth repairing.

SOURCE: auto focus not working

Your Sigma 28-300mm doesn't have a HSM-motor as far as i know. When you switch it from MF to AF, you also have to disengage the manual focusing ring by pulling it towards the camera, or pushing it away from the camera. Using the AF without unlocking the manual focusing ring may damage the AF motor. 
I hope this helps, 
/Chris

SOURCE: Olympus Zuiko 70-300mm lens focus question

Solved

SOURCE: I can't get the macro adapter to work ?

Put the macro adapter on the camera and move the camera in and out from an object to try to focus the object in the display. Remember, macro is very small, very close and very small field-of-focus. I hope this helps.