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Help with Tamron 105mm f2.5 Adaptall 1
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PostPosted: Sat Jun 19, 2021 6:13 am    Post subject: Help with Tamron 105mm f2.5 Adaptall 1 Reply with quote

Hello! I will offer, by way of apology, that I have searched for this lens, for disassembly, and for the specific problem. While I've found reports of the problem, I have not found any resources for the fix.

I picked up my copy of this lens very inexpensively because it has issues. The glass is fine, the focus is fine. There is a small amount of oil on the diaphragm, which may be at the root of the problem. With the Adaptall mount (Ricoh/Pentax) off, the "cam" that activates the aperture does not appear to be as far out of the lens body as it should be. Due to the sticky blades, the tension of the internal spring is not enough for the aperture to operate consistently. With a mount installed, the spring tension in the mount mechanism will operate the aperture...sometimes. Here's the funny part: If the lens is focused to a near point (extended), the contact between the cam and the mount is lost, and the aperture won't work. If it's kept at infinity, it works, but if you focus back to infinity, usually not.

So, what I'm looking for is some guidance gaining access to the rear part of the lens to access the linkage for the aperture. I may have to come in the front as well to work on both sides of the diaphragm, but that looks to be a little more straightforward.


PostPosted: Sat Jun 19, 2021 7:39 am    Post subject: Reply with quote

Hey ektar, I'm not familiar with your lens, but I have opened up and repaired a few different Adaptall-2 models. Internally, they're probably dnot all that different, given Tamron's goal of making a single lens design to which many mounts can be attached.

First: recommended tools: a good lens spanner, an assortment of crosspoint screwdrivers, aka "jewelers" screwdrivers. These can often be found in inexpensive kits. Good thing about these kits is usually they have crosspoint drivers and not phillps drivers. Phillips heads are too pointy and will strip out the screws very easily. It's pretty easy identifying crosspoints. Their heads are blunter, the point is broader and not nearly as pointy as a phillips head. You'll also need a good supply of cotton swabs and some naphtha, aka lighter fluid. Tweezers and needle nose pliers might also be necessary.

I would definitely recommend you find a way to dismantle the lens from the rear. I've never had to open a Tamron from the front to access the iris blades. But when dismantling the lens it often required separating the focusing helical from the lens body. Look for tiny grub screws that hold the barrel sleeve in place. When the screws are removed, the sleeve can often be slid out of the way to get to screws and/or bushings that keep the lens parts from being separated.

If I'm just trying to clean the iris, I will often see if I can access it just by removing components from the rear. After you've removed all the mount hardware, often the lens elements will come out in blocks or groups. I just keep removing them until the iris is exposed. A good lens spanner is an absolute must for this sort of operation.

After I've gotten to the iris, often I'll leave it in the lens and just clean it in situ. When cleaning the iris this way, I will clean it with naptha, using cotton swabs soaked in the stuff. I will make repeated applications until no trace of oil remains, and then I use lens tissue and cleaning fluid on the rear element of the lens that sits just before the irus to make sure all traces of cleaning wipes and/or smudges have been removed.

It's worth noting that this is often not a permanent fix. This is because the oil has migrated from the focusing helical down onto the blades. A full repair involves dismantling the lens and recoating the helical with helical grease, thoroughly cleaning any parts of the lens that shouldn't have any helical grease on them.

Hope this helps.

PostPosted: Fri Jul 02, 2021 5:02 pm    Post subject: Reply with quote

I have the same lens and found that using another adapter point would solve the issue. In my case nikkor is fine, also MR2, but not the FD one,don't ask me why.

PostPosted: Sat Jul 03, 2021 5:11 am    Post subject: Reply with quote

cooltouch wrote:

. . .
Hope this helps.

I believe it's always helpful to someone, somewhere when members take the time to share their knowledge.

PostPosted: Sun Jul 04, 2021 2:41 am    Post subject: Reply with quote

Okay, since info on this one was scarce, I just sorta winged it...

I did not access the diaphragm from the front. It turned out to not be necessary to get it to function the way I needed. More on that in a minute...

After removing the Adaptall adapter, three screws hold the mounting plate in place. Remove those and the plate lifts off. There is then a masking plate in place over the internal mechanisms. If there are screws for those, they just come out and the plate lifts off. There is a semicircular spring that operates the aperture mechanism. It will flick off if you're not careful, but it isn't too hard to replace. The rear element cluster can be grasped with a rubber glove and removed. At that point, you're looking at the back side of the diaphragm. I cleaned that as best I could with Ronsonol, and wiped up what stray oil I could see. I also cleaned the pivots that I could reach. This particular version has an "A-M" switch, like older Takumars (and others). Once I cleaned the aperture, the diaphragm will stop down and open up on M mode, but the spring isn't strong enough for it to work reliably (over the residual oil) in A mode. Since I shoot it adapted to mirrorless, I can live with that. If I get diligent in the winter, I may open up the front and do a similar lazy man's cleanup on the front of the blades. I don't see much oil there, but if I can work some fluid down between the blades from the opposite side, I might get A mode back.

So, that was my experience. If you run up on one of these, and have any lens disassembly experience, this one is straightforward.


PostPosted: Mon Jul 05, 2021 4:24 am    Post subject: Reply with quote

Glad to read you achieved success. My experience with cleaning irises in situ is that, if you flood the iris with enough lighter fluid, it will thoroughly coat both sides of the iris, so there's no need to clean it from the front. Just make sure you remove all traces of the fluid residue from the rear of the element that sits in front of the iris.

PostPosted: Sat Sep 11, 2021 5:36 am    Post subject: Reply with quote

I was having the same problem and was looking for the solution. Thanks to this thread and users, i found multiple solution. i'm try them...Thanks again for the support you guys provided.
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