Firstly, thank you for your time.
The heading Lens Laws was a bit tongue in cheek. There are photography unofficial guide lines to what works and what does not. The understanding I have gained from the Aust. forum made me realise I was heading down a doomed mental path. It is not necessarily that more dollars would give more results.

The reason for the 600 mention was that the focal length of 600 can be recreated on a crop frame using a 400 lens. I have always had trouble settling the comparison in my mind. I have seen beautiful pictures of birds with prey (large an grub sized) that are sharp and clear. I have photos of ospreys that are not cropped that fill the shot. Right place right time.

I think the last time I posted about a lens it was related to the use of a 400 type lens and the weight. I am working on a solution (I hope), as mentioned the 600 size lens would involve a lotto win at least.

Therefore I am wanting to stay in the range of most manufacturers 400, the Tamron has served me well. I believe it is about 10 to 15% shorter than advertised. Using an used shooting target, holding the position of target and tripod I was able to compare the magnified result. The measurement was 120mm on lens a. and 100 on the Tamron. An otherwise excellent lens by most measures.

After some reflection I think that my focus problems are due to my less than steady hands. As long as I have had hands they have never been steady. The obvious fix is to become good friends with a monopod at least and a tripod when needed.

Thanks again for the info you both provided, your knowledge and good hearted distribution are very much appreciated. I now know the direction that I need to walk.
Kind regards, Journeyman (Dennis)