"O<-- -->L" tab

[scott]

I need some basic advice about using a lens I recently bought (a Vivitar 21mm/f.3.8, T4 mount, "Basic Automatic Wide Angle lens").

I can't see the aperture leaves at all. They may simply be stuck open, but I suspect I may also be missing something about the fuction and design of the lens. Also, this lens has some features that my other SLR lenses don't have. Any tips?

The aperture ring feels right as it moves between 16 and 3.8, but even set at 16, I see no leaves. Not even when I press down on the aperture pin. The aperture markings on the lens have a row of white aperture numbers beside a row of green numbers. Why two aperture scales? The aperture ring stays on the white numbers, and I can't make it go onto the green numbers at all.

On the side of the lens, near the mount, there is a little spring-loaded, knurled wheel sticking out. I can turn it about 15 degrees, and then it pops back, but still no aperture leaves. What is the purpose of that wheel, and what is it called? It it like a pre-view button?

opposite the knurled wheel, there is fat tab marked "O<-- -->L", with a little metal spring-loaded trigger sticking out of it. When I hold down the trigger, I can move the ring back and forth about 15 degrees. What is it for? What does it do?

What am i missing?

--scott

[Rachel]

scott said:

opposite the knurled wheel, there is fat tab marked "O<-- -->L", with a little metal spring-loaded trigger sticking out of it. When I hold down the trigger, I can move the ring back and forth about 15 degrees. What is it for? What does it do?

Scott, that unlocks and locks the interchangeable mount. I think that the two aperture scales are there because the aperture ring can move clockwise or anti-clockwise depending on the mount installed.

The aperture problem sounds the same as I have with an M42 CZJ 50mm Tessar. The stop down tab and pin feel OK; that is they have back pressure and feel as if they should be doing something but no sign of the aperture blades. I did think of trying to fix it if it was a mechanical problem but there is only one visible screw on the lens and that is on the aperture ring but I can't undo it.

[PeterW]

Rachel,
On M42 auto-diaphragm lenses (and I think on most auto-diaphragm lenses) the operating pin or lever for the aperture doesn't actually move the iris blades. They are carried on a ring which is spring loaded in the 'closed' position. The ring is held in the fully open position by a catch which is released when you push the pin at the back or push the pre-view tab. How far the blades close depends on the setting of aperture ring which brings a moveable stop into play. When the pin or the preview tab are released the ring is pulled back to the 'open' position.

It sounds a complicated sequence, but when you see the actual mechanism it's quite simple and straightforward. Most cases of non-operation are caused by old sticky oil.

If the iris blades or ring are sticky, as I suspect may be the case with your Tessar and with Scott's Vivitar, the operating pin and the preview tab will feel quite normal in operation but the blades or the ring are stuck enough to resist the pull of the closing spring. Flood cleaning with lighter fluid a few times usually frees things, but oil sometimes washes on to the rear element so if you haven't already removed it you have to take this out and clean it.

It's a long time since I've had a 50mm Tessar apart but as I remember there are three screws on the back face as on the one shown here, a very good photo set of how to take a Tessar apart.

oomz.net/tessar/

The links are also worth following. Lots of useful threads on the forum.

I can't remember now whether you can get to the diaphragm mechanism to flush clean it when the back plate is taken off. If not, you have to go in from the front. Not terribly difficult, but you usually have to have at least two tries to get the three-start focusing thread back in the right engagement or you can't focus at infinity.

I have a niggle at the back of my mind that not all CZJ lenses had screws on the back face, but I may be thinking of some Pentacon lenses, many of which were made by Meyer. On these you have to go in from the front after removing the name ring. Sometimes this has slots for a lens spanner, but if not you have to use a 'friction spanner' like a rubber door stop or something similar.

Good luck if you decide to have a go.

PeterW

[Rachel]

Sorry Scott for hijacking your message Hope my answers to some of your questions are a help.

Peter unfortunately my Tessar is the kind with no screws at the back. The only screw visible is on the aperture ring. Thanks for the links. I may pluck up the courage and try and open it from the front. I never seem to have the time to do this kind of thing but I will try and make some.

[casualcollector]

scott said:

On the side of the lens, near the mount, there is a little spring-loaded, knurled wheel sticking out. I can turn it about 15 degrees, and then it pops back, but still no aperture leaves. What is the purpose of that wheel, and what is it called? It it like a pre-view button?

opposite the knurled wheel, there is fat tab marked "O<-- -->L", with a little metal spring-loaded trigger sticking out of it. When I hold down the trigger, I can move the ring back and forth about 15 degrees. What is it for? What does it do?

Hi Scott,

T4 lenses have interchangeable lens mounts and may be used on a wide variety of cameras with the proper adapter. Press the little springloaded button and turn the ring counterclockwise and you should be able to remove the adapter.

The two sets of aperture scales allow meter coupling with different brand cameras. Aperture rings on Nikon F and Pentax K work opposite most others. The little wheel is a depth of field preview feature.

If the lens isn't working, the adapter may be installed incorrectly. Here's more on T4 lenses.

www.vermontel.net/~wsalati/CasualCollector/t4_for_two.htm

Bill