what F stop to use with 2x TC and 70-300 IS USM lens

hey guys I was wondering what F stop your using for good pics, I know the pics will be softer with the TC already but maybe at a certain level there is a sweet spot or something

I am usually shooting at 300mm with the Tamron 2x tc, the AF does not work at all at 300mm, I have never had it focus properly its just hunting like crazy.

So I guess that is a second question, how do you know if your focus is good or not at that level? the great viewfinder on the XT its very hard to tell. I know there is supposed to be a red dot show up but it never does not matter what I try, at 70mm it works fine thought. I have taken some pics manually and the pics are not that bad but its very hit and miss. I have tried with IS on and off and no difference

the lens itself takes awesome pics though

You are using the Tamron TC, which will probably require you to tape pins, because at 300mm, your lens is only capable of F11. That should give you AF. Beyond that, f11 isn't exactly ideal for much.

What are you shooting that you need the TC for?

yeah I should have mentioned I already tried the tape trick, no difference the thing still hunts like crazy

I am using it to shoot pics of birds, deer etc...

here is one I snapped earlier today, this is at 300 with the TC on there, this was not cropped at all though, when you pull it to 100% you can see the image softness

IMAGE IS A REDIRECT OR MISSING! HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO

tried adding some sharpening to that image? might look OK...