Sky-Watcher Quattro 250P - Collimation Issues

You mean cut circles is ok? I never had that before. And actual focused image is awful, stars is not clean, weird shaped, focused with APT Bakhtinov AID. Images is blurry.
It's feels like i found best focus position, but it's still defocused. I had way better images on GSO 150/750 and no issues with collimation at all. Here i tried seems most of the methods and collimation tools, and zero success as result.

And just to be perfectly clear, mirrors do not deform (permanently) and when they do deform (elastically) they will give astigmatism. But they need to be rather large and rather thin for this to be a significant occurrence, not a typical SW mirror. Show us an in-focus image of a star field. As Alex Nicholas has mentioned before, clipping of the exit pupil image is perfectly normal in a f/4 newton.

Right, I was just making a point here but we'd need still an in-focus image to help you out here. And possibly revise how you do collimate and with what. Autocollimators, are the best way to do that. One issue that has been reported is that SW mirrors have a wrongly positioned donut at the center of the mirror thus collimating against it can only give bad results.

andrea tasselli:
Right, I was just making a point here but we'd need still an in-focus image to help you out here. And possibly revise how you do collimate and with what. Autocollimators, are the best way to do that. One issue that has been reported is that SW mirrors have a wrongly positioned donut at the center of the mirror thus collimating against it can only give bad results.

Last collimation was done using Laser Collimator + "CATSEYE INFINITY XLKP-A". Based on tool instructions, with multiple iterations between Primary and secondary mirror corrections.

I have recently been using my visual scope, a SW 250PDS which also uses the Catseye to take some photos.   When I put my hot spot on , I knew it was not exactly centred and have no issues with collimation; yes there will be a small tilt error which I can get away with at f4.7.   What I did notice that if I collimate my scope vertically and then raise it slowly towards the zentith the collimation moved.  I had it perfectly centred with the Telecat and Autocollimator.   What occurs in my case is that the springs on the back of the mirror do not hold the mirror tight enough.  I never really tightened those locking screws enough.  Your screws may also need that extra firm bit of tightening when collimated so the mirror does not flop too much….

Something that helped determine the state of primary collimation me was to capture an image of a star field and then bring that image into a CAD programme and draw lines in the direction that the comatic stars were pointing in… where the lines intersected was where the sweet spot is (see below). 

Need to remove coma corrector for this to work (I don’t actually bother with a CC so this is easy for me)

In this example the yellow circle has been drawn scale to represent the diffraction limited field size, the circle is pretty close to the centre of the sensor and good enough for me. 

Also it was pointed out to me that sharpcap has a similar tool, which maps star sizes in an image to determine where the sweet spot is on the sensor, this should be faster to do that drawing lots of lines on an image. 

The defocused image you posted may be showing a case of an undersized secondary mirror. If the secondary is too small, the light cone will be progressively cut off as you go further off-axis. This will greatly increase diffraction. In the case of my 8" goto dobsonian, the secondary mirror was so undersized that the extra diffraction caused stars to badly flare towards the center of the image. Once I upgraded to a larger mirror (63mm vs ~45mm if I remember correctly), the problem went away.

My Skywatcher Quattro 250 came with a slightly undersized secondary mirror (82mm), but I've long since replaced it with a 90mm, which gives full illumination across an APS sized sensor (QHY268M).

Although, if you're using the GPU style coma corrector, I know they vignette an image quite a lot (cut off some of the light cone) (I used one for a couple of years and the vignetting was ~40% across my APS sensor) so an undersized secondary may not be the problem. Could you post an image that's in focus?
When I was using a GPU CC, I was also attaching the camera train using a simple 2" compression ring, which caused pinching issues (showed in the shape of the stars). Once I upgraded to a 3" threaded connection, the issue went away.