I've checked again the tension screw (the one below) and loosened it a bit as it was tightly screwed to such an extent that we couldn't move the knob of the crayford !
It wasn't tight so has to require a herculean force, but enough to prevent any move of this knob.
I loosened it so as to be able to very slightly move the knob .
Shall it be very tightly screwed or I should be able to very slightly move the knob ?
I'll give it a try the next clear night (some rain forecasted those days).
Regarding the RC 8 collimation, I've had a devil of a job to do it, I needed all the help I could find in a forum where guys have some real knowledge of RC telescopes and more especially collimation.
I'm quite new to astrophotography, barely 2 or 3 years, so I've already collimated a newton, but RC is indeed a real challenge !
Furthermore, I unfortunately bought it to a reseller that is very bad collimating an RC, therefore I had to do it all over again.
I was also looking for the right "tools" !
For my newton I tried with a cheshire (not so bad), then an Ocal Pro, then the Takahashi collimator and finally the TSRCKOLLI.
I ruled out the Ocal Pro that is supposed to be able to collimate an RC (more adapted to newtons in fact), then I tried with the Cheshire, not so easy with the cross-hair and the donut was very smal, then I tried with the TSRCKOLLI, it was better, the red light and white light (led) was very handy, but it could only be used for the secondary as I eventually found out that I was not using the right circles !
Then I tried again the Taka as many people in this forum used to say, that finally, that was the best fitted for this task !
The point is that everything is ...small when your look through the ocular !
When I finally understood what I was supposed to observe and I was able to focus (pulling/pushing the tube) it was way more easier and now I can't collimate without it !
I keep checking the secondary collimation with the cheshire and the TSRCKOLLI, but I can collimate reliably the primary only with the Taka !
I've spent 3 weeks up to now trying to collimate the RC, I got one night with good quality, but the night after I had oval shape stars on a third of the rigt hand part of my photos, something nobody had ever seen !
So I've done all over again the collimation, and I've now to wait till next clear night to find out if mt colliamtion is good or not.
The point is that so long as it's not stable it's really hard to know when B.F, tilt, guiding problems are involved !
And the EAF issue didn't help ! ;-)
But I'm quite confident, I think I'm now pretty close to the good settings !
Collimation with tools is only step 1, then the next step, collimating with stars is also something I discovered and it took me a few nights to underst and how to know which primary screw to tighten or untighten !