ARTICLE UNDER CONSTRUCTION
I just did my second lens cleaning : a Tamron SP 70-210mm f3.5 (19AH). My first lens cleaning was of a cook triplet 50mm projector lens and that was much easier although I had to clean fungus on all 3 element of that lens. On Tamron lens, the much more complex zoom construction made it harder to access the inner elements and I had quite a few mishaps along the way.
First, why did i want to clean this lens ? I recently acquired an affordable Tamron SP 19AH, I was attracted by its macro functionality and reputed sharpness. But upon receiving the lens I noticed something that looked like tiny oil drops on the back of the front lens group inside the lens. So I though lets just take the front group off and clean it. I did not know the one-day adventure I was embarking on, nor what I would learn.
This post is not intended as a tutorial but it might help you attack the 19AH lens if you have one to repair. I made quite a few mistakes and writing the process will help me on future lenses. This is also a good practical example to the inner working of zoom lenses.
I made a Knowledge post about zoom lenses ( link ) which you may want to read first to better understand the terminology used in this post.
First we can look at the lens schematic which I obtained at the adaptall-2 website. I superimposed an annotation about which lens is from which group so you can relate this schematic with the zoom function.
In my lens tiny oil droplets where contaminating the back of the focus group (annotated in blue in the image above). The Focus group moves when you rotate the control ring of the push pull by being mounted on a helicoid. This front element is all mounted inside a lens tube which is quit easy to remove for cleanup.
Before starting the repair grab some gloves to avoid potting finger marks on the lenses. Some widely available nitril or latex gloves will work very well.
In this lens we can not directly unscrew the focus group. We must first unscrew 3 small screws on the side of the lens barrel (c.f. image bellow). In most lens threads are quite smooth to unscrew so never use excessive force. If some part does not unscrew first try to look whether that element might be fixed somewhere else (like in this case with 3 small screw) or maybe you look it there is a retaining ring on the opposite direction, etc…
