Attention Tamron 24-70 VC owners

Started Jul 28, 2012 | Discussions thread
Daniel Lauring
Daniel Lauring Veteran Member • Posts: 9,344
Re: Problem #2: Aperture lever miscalibration

amateurtony wrote:

I too recently bought this lens (1 week ago). I found it has the lever miscalibrated also. I can tell from running the tests suggest here as well as actually physicall looking at the aperture blades moving. When I move the lever handle, the aperture blades do not immediately move. It only moves after I move the lever about 1mm then does the aperture blades make a noticeable movement.


Being somewhat handy myself, I decided to see if I can manually calibrate it myself so I don't have to waste time sending it anywhere. After spending an hour (learning, reading and then finally got the courage to do it, spent about 10 minutes getting it fixed.


Disclaimer: Try at your own risk! I take absolutely NO responsibility for what you do with this information. You CAN break your lens. Don't blame me if you try it.

Tools: Philips screwdriver, smallest possible. flat head may work too, its what I used.

Philips screwdriver, small size, but bigger than the first one.

Being handy with tools is a plus.

Note: Do not touch the rear lens element throughout this entire process please. You don't want to dirty it up.

Step 1: The mount is metal and inside that mount is the plastic rear with the electrical contacts. There are 4 tiny screws holding this plastic ring in place. Theres also 1 tiny screw that sticks out of the metal mount (ignore this one, don't take it out). Take those 4 screws holding the inner plastic piece out with a tiny eyeglass screw driver. You'll need the smallest possible screw driver you can find to do it. It can also be screwed in quite tight, so be careful not to strip it. The 2 that connects to the electrical contacts are ever so slightly longer than the other two screws, so just remember and keep that separate.

Step 2: Once unscrewed, carefully take the plastic piece on out. The electrical contact piece is free from the plastic ring, but is attached to the lens. Do not take out this electrical contact piece! Just take the ring out.

Once the ring is out, you will see the aperture lever arm attached with 2 screws. These screws are what you need to adjust. Loosen these two screws so you can adjust the lever arm. They are designed to be movable so that it can be calibrated!

step 3: The way I did the calibration is this: loosen the screws

Pull the lever arm on the mount to the end so it contacts the stopper. Keep it in this position with your left thumb the entire time, this is your maximum aperture state. Now you want to move the bottom piece of the arm using the screws. I push the arm ever so slightly at the screws until the aperture blade starts moving. It helps to see the aperture blade if you take the lens cap off, and keep the shade petal on. Once you see the aperture blade start moving, move the screws back slightly so its JUST back to the maximum aperture, and tighten the screws! This part is trick, as you tighten the first screw, the arm will move slightly, so make sure to carefully do this part to prevent moving the arm at all. If you see any movement of the aperture blades, then your maximum aperture will not be 2.8 anymore. If the blades move, just loosen the screws ever so slightly again and adjust again. Do this step right or else you will not have the best results!

Once you get the screws tighten, just fit the plastic ring and electrical contact back the way it was before and screw it back together. You're almost done!

Test the camera and aperture to see if everything works, and if the aperture is correct now!

Thank you. I would like to add what I found with my lens which exhibited similar behavior, and some more do-it-yourself tips.

Couldn't measure a difference between F2.8 all the way to F3.5 with my lens. I took it apart, per instructions and adjusted it, and it was much better, but it still seemed like there wasn't as much difference in exposure, between F2.8 and F3.2, as there was between F3.2 and F3.5, or F3.5 and F4, so I opened it up again and this time I really biased it towards the open aperture side. The result was worse yet. No difference at all between F2.8 and F4. So I went back in and biased it the other opening less, and it worked the best. There is something going on with the calibration that requires the lever to be adjusted in the proper range. It might have to do with the stackup (engineering term) between the base lever, the window in the plastic piece you remove to adjust it, and the camera body's aperture tab.

So, here are my tips.

Tip #1: Before you remove the plastic ring, make note of where the lever is working in the range of the window. If it is moving the blades immediately, and having lots of room on the other end, where the blades stop opening, but the lever keeps traveling, you have an adjustment issue. If it doesn't move the blades for a bit of travel, you probably also have an adjustment issue. You want the entire blade movement to work inside the range of the window.

Tip #2: The screws are small and easy to lose, so work on a white surface. Laying out a white sheet is a good way to go.

Tip #3: A magnetized screwdriver will help you get the loosened screws out, and help hold them in alignment when you put them back in. If you don't have a magnetized screwdriver you can make one by attaching a small magnet to the shaft of your screwdriver...a strong kitchen magnet works.

Tip #4: Zooming to 70mm will move the rear lens element out of your way and you will be less likely to smudge it.

Tip #5: Take a picture of the position of the adjustment screws before you close it back up. If you have to readjust it will help to know where you started from last time, because as soon as you loosen the screws the assembly can move and you won't know which way to move it.

Tip #5: To check your work, use manual mode (M) and switch to manual ISO. Then set the camera up on a tripod and take pictures from F2.8 to F5.6. View the histogram. You should see it moving from light to dark at every aperture change. If it stays the same through the first few apertures you need to readjust it. Test at the wide side (24mm.) It isn't uncommon for constant aperture lenses to not meet there widest aperture at the long end of their range. The Tamron is no exception. There is a much bigger histogram difference between F2.8 and F3.2 at 24mm than at 70mm because the lens is aperture limited at 70mm.

Or...just send it back to Tamron for them to service it.

Good luck.

P.S.  This lens is amazingly sharp even wide open....once you get it there.

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