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01-21-2019, 04:56 PM   #1
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DFA 70-200 over exposing

was using the DFA 70-200 today and it was over exposing everything regardless of my setting i started out in manual and went though everything on the dial and the same thing. it seems to be stuck wide open. it has never done this before and i use it a lot. is there a cure or do i need to ship it ? thank for any help anyone can give

01-21-2019, 05:05 PM   #2
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I've never seen it. What camera are you using? Can you try it on another camera?

What happens if you use optical DoF preview, does it stop down?
01-21-2019, 05:09 PM   #3
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Have you inspected the aperture lever to see if it is moving smoothly?

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01-21-2019, 06:21 PM   #4
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Try setting the camera to bulb mode. Dial in an aperture. Trip the shutter nd see if the lens stops down to the chosen aperture. Then try some other apertures, wide open fully closed and see if the aperture blades are moving correctly.

Regards

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01-21-2019, 07:54 PM   #5
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QuoteOriginally posted by Adam Quote
Have you inspected the aperture lever to see if it is moving smoothly?
yep tried the lever it is fine

---------- Post added 01-21-19 at 09:55 PM ----------

QuoteOriginally posted by Paul the Sunman Quote
I've never seen it. What camera are you using? Can you try it on another camera?

What happens if you use optical DoF preview, does it stop down?
using it on the K1 will try the K3 and see what happens but the DFA 24-70 and an old tamron are working fine

---------- Post added 01-21-19 at 09:56 PM ----------

QuoteOriginally posted by seventhdr Quote
Try setting the camera to bulb mode. Dial in an aperture. Trip the shutter nd see if the lens stops down to the chosen aperture. Then try some other apertures, wide open fully closed and see if the aperture blades are moving correctly.

Regards

Chris
thanks i will try that and see what happens
01-21-2019, 08:06 PM   #6
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QuoteOriginally posted by nitehntr Quote
yep tried the lever it is fine
The issue though is whether the aperture opens and closes with the lever. I have heard of cases with other lenses where a screw connecting the lever to the blades came loose, and they were disconnected. If that is your problem, the aperture would not stop down, no matter what the camera was doing to the lever.
01-21-2019, 08:13 PM   #7
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What metering mode are you using? And what part of the scene was metered? The story does not seem to add up. WHen in manual mode you an pretty much stop down everythign lower the ISO and increase the shutter speed to get a dark (no light) frame. Even if it is stuck at f2.8 the other parameters should help you get the correct exposure provided you are using the correct metering mode (Spot, Center weighted, Matrix)
01-22-2019, 02:17 AM   #8
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did you hit the range limiting switch by mistake?

01-22-2019, 06:37 AM   #9
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ok i tried it on the K3 and the same thing regardless of aperture. i took the front and rear covers off and worked the lever and can see the aperture opening and closing. going to call pentax today to see if there is a quick fix and if not it is under warranty so i will make arrangements to get it repaired. i think i mentioned that the 24-70 and an older tamron 17-35 worked just fine and since then i tried the 28-105 and it did fine also so its in the lens. cleaned the contacts and it didn't change. i am guessing its an electronic glitch of some kind.
01-22-2019, 06:52 AM   #10
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Certainly doesn't sound right, and having isolated the problem to the lens it has to be a problem communicating the aperture setting to the lens. Needs a look into for sure.
01-22-2019, 01:28 PM   #11
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Sometimes the lever is moving smoothly and the aperture is closing but the lever is bent just enough so that the the lever on the lens doesn't engage with the lever in the camera.
01-22-2019, 01:54 PM   #12
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QuoteOriginally posted by pentaxus Quote
Sometimes the lever is moving smoothly and the aperture is closing but the lever is bent just enough so that the the lever on the lens doesn't engage with the lever in the camera.
My Tamron 90mm macro was like that, new straight out of the box! I just straightened it by hand. It has worked perfectly ever since.
4 Days Ago - 1 Like   #13
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thought i would pass on some kudos to precision they repaired my 70-200 and got it back to me in less than 2 weeks and the shots i have taken so far are right on for exposure. they replaced the aperture control arm per the receipt i got back with it. just thought i would also give them some good marks ince i have complained about them being slow in the past.
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