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Can you attach a DSLR to your OTA and take a shot?
My prefered method to check optics for collimation is select a single bright star, centre it and defocus it until it takes up about half the DSLR photo size (so the stars defocused size is about the size of the full moon) and take a 3 to 10 second image and post it here. Such a shot will create a doughnut effect. Then you simply check to see is the dark hole of the doughnut in the precise centre. If not - you need to collimate! Always try and recentre the star before you adjust collimation (so focus star, centre, defocus, adjust collimation, then refocus, re centre, defocus - image check collimation etc over and over).
Once collimated optimally at the centre of your viewing - refocus the star (any Bhatinov mask really helps with this), then move to a object with alot of stars across the whole image. Eta Carina or LMC suit this well enough. Take a 30 second to 2 minute shot and see how curved or flat your field of view is - namely is the centre of your shot nice and tight but the corners streaked or stars strecthed away from the centre. If so you have coma and may need a coma corrector.
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