Tokina AT-X 50-250mm 4-5,6 Lens Separation?

[Gabriel Boin]

I recently picked up the cameras and objectives that my great-grandfather left me from the 70s, and one of those was this big Tokina lens. Inspecting it, I saw those pretty big rainbowy stains, which, without being an expert or close, look like a pretty bad case of lens separation. I'm quite new to this, so I really don't know for sure. Is it lens separation, and if it is, can it be still used, or it's so bad that the lens is unusable? I know that the lens is quite inexpensive and not that good, so it's not worth repairing.
Anyway, thanks in advance for any advice.

 

[Sonnar Brian]

I would try using it with a hood. Off-Angle like this is where you see the greatest effect of the separation. Straight-through, usually much less.

I had a lens like this, simpler design: A canon 135/3.5 in Leica Mount. I used Index Matching Oil used for an oil-immersion microscope lens. Solved the Newton's ring problem.
So- try the lens, know there is a simpler way to fix if there is a problem.