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07-05-2011, 01:57 PM   #1
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Takumar-A Zoom 28-80 3.5-4.5 Question

I know this lens isn't worth much time at all but I have an issue I am trying to figure out. I got this Tak-A used, and while it seems mechanically sound... The maximum f/stop I get from the camera is f4. This is when the aperture setting on the lens is at the A position. I have tried this on both film and digital bodies and I get the same result. It will stop down automatically when the lighting is adequate, but even in low light it never opens up past f4. I can see the iris close a little when a picture is taken so it should be wider? It also stays at f4 at full tele, when it should be f4.5. Now if if I take the lens off of A and manually select an aperture using the lens ring, such as 3.5, it will remain fully open when taking a picture. This kind of defeats the purpose of having an A lens. What am I missing here!

07-05-2011, 02:49 PM   #2
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The number in the VF can be approximate- but if it doesn't open all the way up at 80mm, then there might be a problem.

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07-05-2011, 03:09 PM   #3
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The only way I can get it to take a picture fully open is when I set the aperture manually on the lens. Otherwise it always seems to stop down. I know its hard to describe.

Here's some pics. Camera is in P mode, lens set to A, lens cap on the camera (to simulate low light) and at the full wide/full tele.

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07-05-2011, 03:26 PM   #4
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...its like the lens is telling the camera that the minimum aperture at all focal lengths if f4. Only when set manually will it open up past that. Im just trying to get an opinion so I can sell this lens with proper description.

p.s. - of course when not metering/firing the lens is fully open when mounted to the body (and unmounted when the ring is set to 3.5).

07-05-2011, 06:13 PM   #5
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The KA mount was not designed to account for variable aperture zooms. It can only tell the camera one aperture. So it makes some sense that your lens is always f4 to the camera. But the aperture reported is usually the widest possible number. And it's a little weird that the lens stops down slightly all the time.

It might be a problem with the electrical contacts, consistent with having the issue on 2 cameras. There's a chart on Dimitrov's site that shows how the camera interprets a pattern of open and closed contacts. You might be able to find which contact isn't working by the chart.

Edit: it looks like the contact nearest the lens locking slot might be the trouble. If it's not making contact, the lens tells the camera its max aperture is f4.

Last edited by Just1MoreDave; 07-05-2011 at 08:08 PM.
08-05-2011, 07:29 AM   #6
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I have the same lens and...the same issue. So, I tend to think that there is nothing wrong with your lens...:-).
As for me, with such kind of lenses I always shoot in manual mode.

Tried what you showed on the pictures above - looks good.

Thank you!

Last edited by Vasyl; 08-05-2011 at 07:37 AM.

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