Half Sharp, Half Blur

[Buzzard75]

Not looking for critiques. Just trying to understand what's going on here. I tried imaging M16, M17 and M18 last night with my Canon 750D and my Canon EF 75-300mm lens at 300mm on my iOptron Skyguider Pro. I know the lens isn't the greatest, however, I don't think that explains what's going on here. I checked the lens to be sure there weren't any smudges on either end. This is my final processed image, but even the single raw image shows elongated stars in half the picture. The only thing I can think of is that my polar alignment wasn't quite right. I would expect it to affect stars in the entire image. I'd also expect it to be the opposite and the stars in the other half of the image to be elongated as they are further away from the axis of rotation. Any thoughts and ideas would be appreciated.

[steppenwolf]

I don't think that this is a tracking or polar alignment issue - I feel that that what you have here is a slightly out of focus image that is exacerbating some field curvature deficiencies in the lens itself.