"is it a good idea to BUT lenses for Canon A75.."

I will assume the question is:

Is it a good idea to BUY lenses for Canon A75?

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Some people buy the conversion lenses, but the price of such lenses stops most people.

It sounds as if you found a very good price for the set. I assume you also have the LA-DC52C Conversion Lens Adapter.

Many people buy the polarizer filter to reduce glare and it can produce some stunning sky/cloud shots. The polarizer is most effective when the camera is pointed 90 degrees from the sun.

The UV is used mostly just to protect the camera lens from scratches and such.

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