Orions Sword / Belt

[Mr TamiyaCowboy]

spent some time last night with the canon EF90-300mm F4.5 - 5.6.

coupled to the old 350D canon DSLR , 

Now i have always hated this lens for anything other than telezoom moon images and stacks.

its ok i daylight, but at night its a right pain to focus, like all lenses units without infinity markings.

so i made a bhatinov mask cut it out from some thin printer paper. 

those cheap camlink IR/UV protector cover lenses, yeah i broke it on purpose. removed the glass

popped out the screw ring and slipped my cut out paper mask in. a few clips of the ring screw

and i had a 58mm screw in bhatinov mask for camera lenses. 

next came the testing, i focused up for 300mm and grabbed three images ( added for others to see)

one is slightly to much on in focus, one slightly to much out focus, and one bang on.

next setting lens to 90mm and refocusing on Spica, my difractions were very shallow

but i guessed and slammed of a shot all shots are pure RAW to jpg conversion, no messing or tweeking.

each image is a twenty second exposure at iso800 F5.6 @ 460mm (1.6 canon crop factor) 

the single orion image is iso 800 20 seconds @144mm (again canon crop factor here)

image 1 : here we are slightly out of focus, my center line is not center 

Image 2 : here its flipped now slightly in side focus

Image 3: ah perfect, nearly thats about as good as i could get

Image 4 : i took this one in tungsten, all the hue you see if from one single new energy saving street lamp ( the white bulb ones)

How do i get even closer to bang on focus with my new masking ?

how can i kill this white light pollution. orion was at max hight i took this shot