Orio wrote: TamronSP wrote:
I looked at the links for the optical design. It isn't the rear element which is flipped because you would notice that and the off-axis astigmatism which would result.
Apparently the curves on the front element are slightly different on each side. So, it MUST be the front element which is flipped. Now that is pretty easy to fix, isn't it? You can fix it yourself if you have a spanner tool (assuming that the front element is held in by a retaining ring.
I'm a disaster at handbased jobs
Figure that at junior high I used to have 7 or 8 in all disciplines (here the maximum vote used to be 10, but rarely they gave more than 8), and only had two 6 (the minimum sufficient), in maths and in "technical applications". And it was more or less a "given" 6, not deserved.
But I guess that I can't make it less useful than it currently is, so maybe I can give it a try.
By front element you mean the front lens I guess, the one that is external - or maybe the one internal that is behind it?
See - I'm a total inept at this kind of stuff
Thanks for the precious help anyway!
Yes, I mean the frontmost element -- the one that is external. This is possibly the one which is flipped. It also occurs to me that the two frontmost elements, as a group, could be flipped. Thinking about the excessive spherical aberration which your photos show, I now consider this to be the most likely possibility. To check this, have a look at the surface of the front element of your lens. The optical design shows that the front element is convex with similar curves on both sides. Thus the front surface of your lens should have a visible curve. If on the other hand it appears to be quite flat, then both of the front elements are flipped as a group.
If you determine that the front elements are flipped as a group, then:
1. Remove the front retaining ring. Hold a soft towel over the front of the lens and tilt the lens upside down so that the two front elements will drop out onto the towel. If the elements don't want to easily drop out, carefully set the towel and lens (upside down) onto a table and use the plastic handle of a screwdriver to gently tap around the outer barrel of the lens. The vibrations from the tapping should allow the front elements to eventually float down and drop onto the towel.
2. Now that you have the elements out (and the spacer ring which is between them), you can put the lens aside after using a can of compressed air to gently blow out any dust within the lens.
3. Grasping on the outside edges, carefully pick up the front elements (with the spacing ring between them) together as a complete unit, flip them over, and set them back onto the soft towel.
4. Using your fingers, carefully center up this stack of two elements and the spacer ring in between them.
5. Take the lens, center it up over the elements, and carefully lower it onto the elements such that the elements begin to go back into the lens as much as possible. If the elements get wedged or stuck, repeat step 4 and try again.
6. Slide your fingers under the towel and pick up the elements and lens. Don't turn the lens over yet. Instead, see if you can use your fingers under the towel to continue pushing the elements back into the lens until they stop. Carefully flip the lens over.
7. The elements should be back in their cell now. Tap around the sides of the lens barrel just to be sure that the elements have settled down all the way into their cell.
8. Install the retaining ring until it just makes contact with the front element.
9. With the lens vertical, gently tap a few times around the outside barrel, and then tighten up the retaining ring slightly more.
10. Repeat step 9 as long as the retaining ring "wants" to tighten up a bit more after tapping the barrel.
11. The retaining ring now should be reasonably tight. We know that the elements are centered due to the efforts of steps 9 and 10. Now you can tighten the retaining ring until it is moderately tight.
12. You are done! Take some test shots. Wide open, images in the viewfinder should appear to be nice and crisp.
If you determine that just the front element is flipped, then:
1. Remove the front retaining ring. Hold a soft towel over the front of the lens and set the lens on its side on a table. Now, let the towel lay flat in front of the lens. Slowly lift up the back of the lens and tap the side of the barrel with the plastic end of a screwdriver. The frontmost element and possibly the spacer should drop out, but the rear element should stay in the lens. Lay the lens back down horizontally on the table.
2. If the spacer ring fell out along with the front element, pick up the spacer and insert it back into the lens.
3. Grasping on the outside edges, carefully pick up the front element, flip it over, and insert it back into the lens while holding up the front of the lens slightly. If the element wedges, repeat steps 1 and 2 and try again.
4. With the element flipped and back in the lens again, follow steps 7 through 12 of the above procedure.
It occurs to me that someone might have deliberately flipped the front two elements to create a "soft" lens for portraiture. Using an old lens, this is a dirt cheap way of creating a soft lens which sharpens up when using smaller apertures.
Anyway, the above procedures are straightforward to do if you have a spanner tool and mentally think the procedure through before starting. And remember that patience is a virtue.
for information about vintage Tamron manual focus lenses.