Two different aperture readings from Copal #0 shutter--which one is correct?

I have had this Schneider Symmar 135/5.6 for a while now and I have noticed from time to time that the sliding aperture indicator on the Copal #0 shutter gives two different readings depending on whether you look at it from the front or from the side. The section of the aperture indicator that hugs the side of the barrel of the shutter is bent to the right, so the reading from the arrow on the side of the shutter will always be 1/2 stop slower than the reading on the front. (e.g. If the arrow on the front reads 11, the value indicated on the side will be 13--halfway between 11 and 16.) The little metal arrow for the side reading is not affected by the bend in the other indicator, to which it is connected from inside the shutter.

Here are some things that you should perhaps know about the lens:

I bought it used from an advertising company that had used it to shoot slides and they were very straightforward with me about what was right/wrong with the lens, even sending me the appraisal report--in which the bent aperture indicator was not mentioned. (Things that were more serious/difficult to fix WERE mentioned.)

I was never really too troubled about this problem because I was mostly using this lens to shoot B&W,with which I always over-expose a stop anyway. The B&W negs I have shot using this method look nicely exposed and have good shadow detail with no push/pull. Even when I shot color with this lens and consistently used the reading on the front, I did not detect any significant under-exposure. But I never, in fact, bracketed exposures 1/2 stop apart to check. I scan all my LF film for printing, so one stop doesn't usually make a difference. Now, however, I am shooting slides, so I want to eliminate any possible exposure variables that I can take care of.

With the front arrow set to 5.6, the aperture width is about 16mm. With the side arrow set to 5.6, the aperture width is about 18.5mm. With the blades wide open, you get close to 24mm. (But that seems wrong. Why should the ratio of focal length-to-aperture width only reach 5.6 when the lens is wide open BEYOND its usable limit? I thought the whole idea with a lens like this was that you got 4.0 or 4.5 for focusing, but that the widest useful aperture was achieved when the lens was stopped down a little. So a lens marked f 8 can actually be focused at f 5.6 and so on. Here, regardless of whether the indicator arrow is bent or not, you get to the point marked f 5.6 on the shutter only when you stop down a little, but arithmetically you only get f 5.6 when the lens is wide open. Or am I missing something?)

Or maybe the bent arrow is supposed to be like that? Somebody changed it to compensate for some other mechanical error that was interfering with the aperture indication?

Any advice would be greatly appreciated.

Rafil

I think you have a 135-235/5.6-12 Symmar convertible ! If you use it like it (135), you must use the f scale that start at 5,6...if you remove the back element you have an other focal length (235), and then you must use the other f scale... but i don't know a lot about this type of lens, you should search in the archive for "convertible lens 135 " to find out more about it !

Look throuhg the front of the lens. Open the shutter until the aperture blades just clear the opening. Now check which scale reads 5.6 - that is the one to use.

Symmar's don't open up to more than 5.6. The opening should be about 135/5.6 mm, or 24.1mm. so you may have a shutter with aperture scale for a different lens!

If you want to use it at 235mm, the scale should start at f:12. And unlike what the previous poster said, you always unscrew the FRONT element to convert it to 235mm. Always use the rear element, the front can be removed.

Yes, it is the 135/235 5.6/12 convertible lens. However, the numbers are paired for both of the the f-stop scales (5.6=12, and so on), so the different front/side scale readings have nothing to do with the relative speeds of the two lens configurations.

Hmm. Is it possible the shutter is mis-calibrated for use with this lens? Must be something like that. As I mentioned before, even when the side scale just makes it to 5.6(/12) and the front scale is still reading a stop faster than 5.6(/12), the aperture is already reduced from a diameter of 24.1mm to about 19mm, which is a lot more than having the blades "just clear the opening." In fact, at this setting (with the shutter's side reading at 5.6/12), there is about 2.5-3mm of blade width circling the inside of the barrel.

I don't suppose there's any good way to check this with a spotmeter? Should I maybe also measure the smaller apertures to see if there the f-stop readings are consistently off by a certain amount so that I can compensate for them?

I don't have a 135mm Symmar, but I do have a 150mm (and a 240mm). I just measured the opening when the aperture is at f:5.6, and got about 27mm - blades just clearing the opening. So yours should be (or should have been) about 24mm to be correct at f:5.6.