Check Camera Focus
Helpful to buy something like this
https://www.amazon.co.uk/gp/product/B012F8G1DO/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
There are bigger targets (more expensive) or you could build your own with a ruler set at 30 degrees.
Watch
https://www.youtube.com/watch?v=52fBIp4BI84
Back Button & Setting Up Focus (Using Canon) by Simon Mee