Vielleicht helfen diese Hinweise hier weiter:
[Is it worth fixing/cleaning on this Tamron 55BB 500mm f/8.0 mirror - PentaxForums.com](https://www.pentaxforums.com/forums/...-0-mirror.html)
Zitat von Nutzer "MattGunn": "I have fixed two of these lenses and they are amongst the easiest lenses I have ever worked on. The main reason for this is that there is no aperture and so no aperture mechanism. The only moving part in this lens is the focus helix and it isn't necessary to open this to get into the lens. [...] If you want to have a go yourself then it is posible to get at everything you need to from the front. With a spanner wrench (or an old pair of dividers or calipers etc) remove the retaining ring on the front. You should now be able to remove the front element and although it is a few inches inside the housing you can now get at the mirror front surface. You don't have to worry about damaging the reflecting coating as it is on the back of the glass mirror substrate (this is really a back silvered lens). I cleaned a lot (a LOT more than is visible in the photo above) of dirt and fungus of the mirror on one of mine this way using cotton buds (Q tips?) without any difficulty."
... und noch ein YouTube Video mit einer Anleitung zum "Zerlegen" des Objektivs zur zur Reinigung des Spiegels:
[Tamron SP 500mm mirror lens, stripped to clean fungus from mirror.](https://youtu.be/bVETiHIM4Es)