Like this worked for me for an obvious correction on a doublet. Three LED on the back of a cheap 72mm to t2 adapter. Maybe 50mm would work. I used an adapted camping light but you can buy a three led disk online.
The spacing of the led needs to be at least 20mm centre to centre to give enough separation for naked eye adjustment viewing through a 5mm hole in the centre.
You can also use an eyepiece projection tube and two old stacked Plossl to get focus for a closer view.
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