Scratches or sticky residue and should I worry

[pippo1234]

I've bought a second-hand Nikon Plan 40x 0.65 160,.17 on eBay. Cost 60GBP.
Looking through it, both with the naked eye and using a telescope lens, shows some extensive markings I am not sure how to classify. My best guess is some sticky residue, but it's not an oil objective. I would venture they are not on the front lens. Cleaning the front lens with lens cleaning liquid made no difference.

I am attaching two pictures (the same picture with two different post-processing). In use, the image quality seems very good, but the buyer accepts returns. Any advice would be most appreciated.

[MicroBob]

Hi,
I would interpret this as dried immersion oil and a little dust that is stuck in it. The 40:1 has little free working distance and often gets dunked in immersion oil. Many plan objectives have a concave front lens that is a bit more difficult to clean in the middle. So I would try to check wheter this is a substance on top of the glass surface and in case try to dissolve it.

Bob

[pippo1234]

Solved it. Many thanks!

Your point about the concavity of the front lens (indeed it is) was crucial. Previously I had tried to clean it with a microfibre cloth dabbed in either lens cleaning liquid or isopropyl alcohol without success. Once I understood that the concavity might be a hindrance, I tried a fine conical cotton swab dipped in lens cleaning liquid and ... lo and behold!

It is a great objective, at least compared to the Vickers ones I am used too. I have a phase-contrast Labophot 2 on its way. The Vickers was a great first step and a cheap way to test my interest. I appreciate your advice at the time.