Collimation error, or is it?

[Ledge1962]

Hi all,

A bit of a moan here, but also something other amateurs like myself "may" need to be aware of. I could be wrong with my "assumption", so feel free to correct me.

I was collimating my Dob with the standard peep sight to put the secondary mirror in the centre of the sight tube. I even took a photo and measured the distances to get it close   I then aligned the primary mirror reflection so it was centred in the mirror as per the standard procedures. Everything was lined up nicely and the primary centre spot was (no pun intended) spot on. 

I read an article on configuring your secondary mirror more precisely as I was not sure of my abilities to do so using the peep hole. The directions said to first put the  cross hairs on the sight tube over the centre mark on the primary mirror regardless of where everything else was. So, I put the crosshairs on the primary and adjusted the secondary collimation screws until the primary centre spot was under the cross hairs. BUT, no matter what I did, it put the secondary mirror way off the perfect centre and nothing I did (following the rest of the logical instructions) would get the cross hair over the centre mark while the secondary mirror properly reflected the primarys centred reflection.  In the end I went back to just lining everything up with the peep hole, but wondered why it wouldn't work...  

My assumption... I took the photo down the tube and overlayed it with a symmetrical cross hair lined up with the vertical wire on the tube. This is what I got. 

I do not know if this is enough of an error to stuff everything up, so could the more learned Users comment please.

Thanks

George