is it worth upgrading a nikon 70-300 to a sigma 150-500mm w

[iwols]

hi all first post from a relative newbie so please be careful please....ive been using a standard kit nikon 70-300mm lens on a d90 with a kenko x2 converter and tripod to photo the birds in the garden etc,and the pics have come out ok,but not 100 percent sharp,shooting everything on auto at the minute(i know i should learn),and was just wondering if the sigma 150-500mm would be a better option and has anyone used a 1.4 or 2x kenko converter with this lens,any comments remarks appreciated

 

[Chrisbie]

is this the VR version of the 70-300
I used one with a kenko pro 300 1.4 TC and to be honest it was poor but is a great lens without it. Cropping was better by far.
I also had a Sigma 150-500 and it was OK when it worked but we had to part as it stopped focusing properly.

 

[gad-westy]

I think you need to establish why you're not getting the results you want with 70-300 first. If it's the VR model, it's a great lens but maybe something isn't quite right in your technique. For example, you mention that you're using auto exposure, do you know what sort of shutter speed you're achieving?

The kenko converter. Does that still allow auto focus or are you focussing manually? It will also degrade the image, as all converters do to some extent.

Are you on a tripod or handheld and VR on or VR off?

The 150-500 is a nice lens but I think you need to check you have reached the limits of your current equipment before shelling out.