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07-08-2010, 01:03 PM   #1
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43 mm 1.9 metering Problem

Hello,

I have a K7 and a 43mm lens. All my other lenses are fine but I cannot meter properly with the 43mm lens. When I use it at F4 or wider I have to set the EV to -1.0 or -1.3 but if it is at F8 or higher it will only work at -3.0 to -5.0 Ev.

Is this normal? Or how can I use this lens better.

I want to sell it because it isnt very useful for my travels... but I also dont want to sell it to someone if there is a problem with the lens.

Steve

07-08-2010, 01:18 PM   #2
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QuoteOriginally posted by stevemgap Quote
Hello,

I have a K7 and a 43mm lens. All my other lenses are fine but I cannot meter properly with the 43mm lens. When I use it at F4 or wider I have to set the EV to -1.0 or -1.3 but if it is at F8 or higher it will only work at -3.0 to -5.0 Ev.

Is this normal? Or how can I use this lens better.

I want to sell it because it isnt very useful for my travels... but I also dont want to sell it to someone if there is a problem with the lens.

Steve
Is this a KA or K mount lens.

I find K mount lenses lead to metering errors on most cameras.

see the following post

https://www.pentaxforums.com/forums/pentax-beginners-corner-q/99621-m42-lens-...ml#post1029553

but I find your adjustments a little exagerated, perhaps double from my experience with the K7
07-08-2010, 01:25 PM   #3
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QuoteOriginally posted by stevemgap Quote
Hello,

I have a K7 and a 43mm lens. All my other lenses are fine but I cannot meter properly with the 43mm lens. When I use it at F4 or wider I have to set the EV to -1.0 or -1.3 but if it is at F8 or higher it will only work at -3.0 to -5.0 Ev.

Is this normal? Or how can I use this lens better.

I want to sell it because it isnt very useful for my travels... but I also dont want to sell it to someone if there is a problem with the lens.

Steve
Is the aperture not closing down properly when you take a shot? If the camera body things the aperature is set to f/8 but the lens never stops down, then you'd be off about -4 EV (camera body thinks the lens is at f/8, but the aperture is wide open). When you're at f/4, you'd have the same problem if the aperture isn't closing down properly, but you'd only be off by about -2 EV. At least I think that's what would happen. Hopefully someone else can chime in if I'm way off base.
07-08-2010, 01:41 PM   #4
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Nope, that sounds just about right.
Sounds like a 'sticky aperture'.
Release the lens from your camera and check to see that firstly the lens is on the 'A' aperture setting, then check to see that the lens aperture blades are closed right down. If not, they're stuck and should be released by the little aperture lever on the inner edge of the lens. Be gentle with it, though, it's delicate and important to keep intact.

If it's released manually and gets stuck again when you shoot with it, it should be serviced. And if it's stuck and won't release then it should be sent in for a repair also. Let us know how you go.

07-08-2010, 01:44 PM   #5
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Your Pentax-FA 43/1.9 Limited should work just fine with your K-7 with the aperture ring on the "A" setting in all modes. If this is not the case, there may be an issue with the lens. When the aperture ring is on other than the "A" setting, you must use the camera in "M" mode with green button stop-down metering. Again, the camera should meter properly at all apertures.

It was not clear from your post whether you thought the meter reading itself was wrong or that the lens was not stopping down properly for the exposure. You can rule out the lens by a simple test:
  1. Use a blank wall with consistent illumination for a target and put the meter on center weighted averaging
  2. Put the aperture ring at the "A" setting and the camera in Av mode
  3. Starting at the smallest aperture, record the shutter speed at 1 stop increments (f/22, f/16, f/11, f/8, f/5.6, f/4, f/1.9)
  4. Take a photo of the blank wall at each step
  5. Each shutter speed step should be half that of the one before it
  6. The images from each exposure should have the same brightness
If the test fails at step 5, the camera meter is at fault. If the test fails at step 6, the lens has a faulty aperture.

Steve

BTW...I am assuming that you are using the stock focus screen...

Last edited by stevebrot; 07-08-2010 at 01:51 PM.
07-08-2010, 04:13 PM   #6
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QuoteOriginally posted by stevebrot Quote
Your Pentax-FA 43/1.9 Limited should work just fine with your K-7 with the aperture ring on the "A" setting in all modes. If this is not the case, there may be an issue with the lens. When the aperture ring is on other than the "A" setting, you must use the camera in "M" mode with green button stop-down metering. Again, the camera should meter properly at all apertures.

It was not clear from your post whether you thought the meter reading itself was wrong or that the lens was not stopping down properly for the exposure. You can rule out the lens by a simple test:
  1. Use a blank wall with consistent illumination for a target and put the meter on center weighted averaging
  2. Put the aperture ring at the "A" setting and the camera in Av mode
  3. Starting at the smallest aperture, record the shutter speed at 1 stop increments (f/22, f/16, f/11, f/8, f/5.6, f/4, f/1.9)
  4. Take a photo of the blank wall at each step
  5. Each shutter speed step should be half that of the one before it
  6. The images from each exposure should have the same brightness
If the test fails at step 5, the camera meter is at fault. If the test fails at step 6, the lens has a faulty aperture.

Steve

BTW...I am assuming that you are using the stock focus screen...
note that the lens, out of A mode will not meter correctly.

see the above link in my post. although the K7 is better than the K10/20 in metering, it still has errors.
07-09-2010, 11:50 AM   #7
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QuoteOriginally posted by Lowell Goudge Quote
note that the lens, out of A mode will not meter correctly.

see the above link in my post. although the K7 is better than the K10/20 in metering, it still has errors.
I intentionally left out testing in "out of A" mode from my suggestion due to a degree of uncertainty regarding the results.

According to the K-7 manual (K-x too), the meter should work fine if in M mode with the lens off the "A" position. I don't own the camera, but have tested this using a demo K-7 and my M 50/1.7 using the method described above and experienced the expected meter linearity and proper exposures. I am not saying that you are incorrect, only that that my experience has been different. Since I don't own the camera, I can't say how it might behave for other non-A lenses.


Steve
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