Tamron SP 1:5.6 350mm, rear lens element needs cleaning?

[hoacker]

Hi there. Today I've received a Tamron 350mm mirror lens. It's the version with tripod mount collar, which is the earlier one, if I'm not mistaken. I knew from the description that a rear lens is not clear, but definitely no fungus. See the picture below for the mess. The lens was quite cheap accordingly. I've done only few test shots despite terrible weather an have not seen an effect on the image taken. I will not rule out that the "dirt" has effect in brighter light conditions.

- Can someone tell what these stains are? Bad coating?
- Is there a guide for disassembling the rear lens elements? I'd try to clean the affected element.

Thanks in advance.

[ManualFocus-G]

I've had something similar before on a Tamron 500/8, does the effect appear rainbow like? On the 500/8 is reduced the light transmission, meaning slower shutter speeds

[Attila]

It's actual value around 500 USD worth to pay for proper service. Try it out before touch anything, may works well.